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View Full Version : Best way to ream to 0.944"?



tylernt
12-31-2010, 07:21 PM
I'm trying to rebuild an engine and I installed some new wrist pin bushings in my connecting rods. Only when I went to install the wrist pins did I find that the bushings are shipped deliberately undersized so they can be reamed to fit the wrist pins. Since I have a drill press and mini-lathe, I wondered if there was a way to do this myself.

I can buy an 'H' sized hand-reamer, but the wrist pin bushings are split bushings, so each blade of a straight hand reamer might hang up in the split seam (there's not much of a split -- the two ends are pretty well wedged against each other -- but I can still feel a notch there with my finger). So rather than ream by hand, I wondered if I could use a hand reamer in a drill press or lathe spindle to keep that split seam from messing things up? Either under power, or just spinning the chuck or spindle by hand.

Unless there is such a thing as a large spiral-flute adjustable reamer? I see a few of them on eBay but they are way too small for a hole nearly an inch wide.

One thing that worries me is the tolerance of the final bushing ID is .0005" (half a thou), and I'm not sure that I, as a newbie, can hold this tight of a tolerance. My dial calipers are only accurate to .001", for example.

Any suggestions? I accidentally ordered 4 sets of wrist pin bushings when I thought they were sold individually, so I can mess up quite a few of them before I give up and go to a real machine shop. ;)

hardtail
12-31-2010, 07:31 PM
Don't power a hand reamer.....they are too aggresive for that......

Split bushings can be reamed......how close can you get without me doing the math.......

For first time attempt you may bellmouth the bushings by hand......

How much under are they?

Are they bronze?

They make small hones for this in auto specialty tool stores if you are close to final size already......crude might even be a fine flap wheel or some emery in a slit rod and patience......how many rpm, what kind of engine?

.0005 never changes but an antique stationary pump verses a 2 stroke dirt bike will be different applications.......grin

tylernt
12-31-2010, 07:43 PM
The old bushings were bronze-colored. The surface of the new ones is silver, but I see a layer of bronze underneath, where I drilled through for the oil holes.

They are .020" undersize right now.

Hm, a brake master cylinder hone might be about the right size. Not sure if .020" is considered "close" though.

This is for a VW 1.6L turbo-diesel of about 100HP.

hardtail
12-31-2010, 07:50 PM
The old bushings were bronze-colored. The surface of the new ones is silver, but I see a layer of bronze underneath, where I drilled through for the oil holes.

They are .020" undersize right now.

Hm, a brake master cylinder hone might be about the right size. Not sure if .020" is considered "close" though.

This is for a VW 1.6L turbo-diesel of about 100HP.

I wouldn't recommend the brake hone either......the hand reamer would probably be the better way to go.......the brake hone will probably bellmouth faster.......can you accurately measure the reamers settings and bore after?

tylernt
12-31-2010, 07:55 PM
can you accurately measure the reamers settings and bore after?Not really, my dial calipers are only accurate to .001". Can I just ream a bit at a time until the wrist pins just barely fit in the bushings?

SGW
12-31-2010, 08:02 PM
Check here: http://www.lavallee-ide.com/
If need be, you can order a custom size, though the price might be a little high.

RussZHC
12-31-2010, 08:10 PM
something like this ?:

http://www.victornet.com/subdepartments/Hand-Expansion-Reamers/1820.html?id=T8diwShT

tylernt
12-31-2010, 08:22 PM
something like this ?:

http://www.victornet.com/subdepartments/Hand-Expansion-Reamers/1820.html?id=T8diwShT
Hey that's it, a spiral flute adjustable hand reamer that goes up to the right size! $99 though... so now the question is, is a $36 straight flute reamer going to be "good enough" or is the spiral flute really needed for this split bushing?

Pic:

http://i54.tinypic.com/s6oi07.jpg

becksmachine
12-31-2010, 08:24 PM
I would suspect that you have more than one problem here.

Reaming to a tolerance like that with an adjustable reamer is in the realm of art, not science. You should get them all within .002-.005 before trying to hit a specific finish size. In other words if you sneak up to the proper adjustment on the first one, adjusting and measuring 4-10 times, and then think that the reamer is set to ream the other rods that still have .020 in them, the reamer will almost surely cut oversize.

The previous comment about bellmouth is right on. To that I would add squareness as a major concern. Without a jig to guide the reamer you have no way of knowing if the hole you just spent 15-45 minutes reaming to a nice push fit is anywhere near parallel to the bore in the big end of the rod.

Not wanting to throw cold water on your plans, just trying to help someone avoid some of the mistakes I have made. ;)
Dave

J Tiers
12-31-2010, 08:24 PM
Spiral will work better.

tylernt
12-31-2010, 08:45 PM
The previous comment about bellmouth is right on. To that I would add squareness as a major concern. Without a jig to guide the reamer Let's say I sweep a dial gauge in my drill press chuck on the machined face of the conrod big-end bore (same way you tram a mill). Assuming this machined face is square to the big-end bore, I can adjust my drill table to get the rod square to the quill. Now I just use my drill table to hold the small-end of the conrod, put light pressure on the quill, and turn the reamer by hand.

Workable?

Admittedly, this is a crummy Chinese DP but I hope the reamer is self-centering enough when turned by hand that a bit (well, actually, a lot) of runout in the DP is not going to hurt anything.


Not wanting to throw cold water on your plans, just trying to help someone avoid some of the mistakes I have made. ;)
Much appreciated. :)

Arcane
12-31-2010, 08:46 PM
This might be better done at an automotive engine rebuilder's shop. They are set up to do this job with all the tools and measuring equipment and can hone it out to a .0001 (and yes, rod end clearances are a matter of a few ten thousandths) with ease. You have to keep the rod bore exactly parallel to the crankshaft while you do it. Can you do that in your shop? Guaranteed? It's important...if the bore isn't parallel, the oil film is going to be compromised when the engine is running. One end of the bushing is going to have much tighter clearance on one half of the stroke and the other end will have the same problem on the other half of the stroke, and on the opposite side of the bushing. If it cuts through the oil film, you will be into metal to metal contact and all that implies.

I'm not saying this can't be done in a home shop environment, just that there is more to it than meets the eye.
Since this is in a VW 1.6L turbo-diesel engine, it stands to reason that it is something you want to have right the first time since it's a LOT of work to correct it if problems arise.

rohart
12-31-2010, 08:54 PM
I had a lousy time using an adjustable reamer. Never again. Grab, stick, go off centre, and that's after setting up a jig to keep it in line.

If you were worried about grabbing at the split line, the worry would be in case your bush turned, wouldn't it ? Can you make a small fitment to go into the oil hole you drilled and stay just below level. This would prevent the bush from turning, split or not.

Anyway, when you say .944" do you mean .9448 ? If so, then that's 24mm. Standard metric size.

Arcane
12-31-2010, 09:18 PM
Edited to remove wrong post.

Don Young
12-31-2010, 09:26 PM
Arcane has the right ideas. You cannot successfully ream those bushings with anything other than a special purpose fixed spiral reamer or a spiral fluted 'expansion' reamer (not an 'adjustable' reamer). They could be accurately sized with a Lisle Small Bore Hone or similar tool. These have controlled expansion, not spring loaded.

After sizing the holes the rods would need to be checked on an alignment fixture. All told, replacing pin bushings is not a simple job and you are well advised to take your rods to an automotive machine shop. They will likely use a Sunnen hone to size them. Even regular machine shops are often not well equipped to do this type of work.

oldtiffie
12-31-2010, 09:44 PM
http://www.victornet.com/productthumbs/787.jpg

If needs be buy a bigger spiral reamer and have a friend who is good at tool & cutter grinding to re-grind it to size.

If it were me, I'd set the inserted sleeve (in the connecting rod) up in the mill and use a boring head to bore it to reaming size. Remove the boring head and insert the taper reamer and ream the hole in the same set-up.

jkilroy
12-31-2010, 10:09 PM
Have buddy with a rod hone machine? Is your lathe big enough to strap the rod to a faceplate and bore it? (Sorry if thats been covered?)

oldtiffie
12-31-2010, 11:08 PM
The penny just dropped here.

The OP is only using calipers so he could be "out" a "thou" easily.

The engine is a VW - which is metric.

The 0.994" given by the OP is actually 23.9776mm which is very close to a nominal 24.00mm.

I'd check the wrist pin/s with a good micrometer to confirm their sizes.

I've bet that a VW dealer or mechanic will have the reamer required. Why not get them to do the reaming for you as they will get it right.

Getting the bore the right size is one thing but getting it accurately square to the axis of the connecting rods is very important too.

mf205i
12-31-2010, 11:25 PM
Fixture the big end to your cross slide and then bore the small end with a boring tool at the spindle. That being said, this would be a great time to purchase some quality measuring tools.
Good Luck, Mike

doctor demo
01-01-2011, 02:13 AM
Arcane and Don are where Your thinking should head to. An automotive or diesel engine rebuild shop is going to do those for You cheaper than the reamer can be purchased, and You wont have to buy new bushings to replace the reamed ones .
I applaud You for wanting to do it Yourself but there are times to know when to say when.

Just My .002$

Steve

davidwdyer
01-01-2011, 05:41 AM
I think OldTiffe may have something there.

If this is metric, then the reamer could be a standard metric size and therefore much cheaper.

John Stevenson
01-01-2011, 07:51 AM
We used to do these all the while when we had the truck garage, never knew a bush that came prefinished.
On some you had to take that much out there was hardly any bearing material left, I often thought they were using a stock bush and not one for the job, Ford was worse at this.

We used decent quality expanding reamers that went from 5/8" up to 2 1/2", still have the set somewhere kicking around in a big tin box.

The trick is to creep up on the size, bit at a time, one pass from one side, adjust and then do it from the other side to stop it wandering and bell mouthing.

Decent expanding reamers are made with the slots for the blades offset and they usually have odd numbers of blades to stop the threepenny bit effect of bumping from slot to slot.

I have another small set here up to 1" and these have equal number of blades and can be a bitch to use, if they start threepenny bitting, you are doomed.

[EDIT] Just thought, many may not know what a threepenny bit is.
it was an old coin of the realm before decimalisation, very useful coin as it didn't roll.
handy for wedging behind the cold start mechanisms of old diesels to get max fuel :D


http://www.istockphoto.com/file_thumbview_approve/1191375/2/istockphoto_1191375-threepenny-bit-old-english-coin-1967-reverse.jpg

.

mike os
01-01-2011, 09:14 AM
looks like you need 2-3 tools before even attempting this... internal & external mic's, and the correct reamer.....

Personally I would have it done.... costs less than one of the mic's

John Stevenson
01-01-2011, 09:26 AM
You don't need any measuring equipment, you have the wrist pin.
Just keep taking a bit out and trying the pin.

tylernt
01-01-2011, 02:21 PM
Fixture the big end to your cross slide and then bore the small end with a boring tool at the spindle.

Have buddy with a rod hone machine? Is your lathe big enough to strap the rod to a faceplate and bore it? (Sorry if thats been covered?)My mini-lathe is too small to faceplate the rod, but bolting it to the cross-slide sounds promising. Assuming I use a fixture on the big-end bore, that should make the small-end parallel within the limits of my lathe's accuracy... which I doubt is .0005". ;)

However, fixing the rod to my drill press table which has been dialed in square to the big-end with an indicator sounds plausible, no? I would hope using a hand reamer in this manner would be more accurate than free-hand reaming?


Arcane has the right ideas. You cannot successfully ream those bushings with anything other than a special purpose fixed spiral reamer or a spiral fluted 'expansion' reamer (not an 'adjustable' reamer).
...
All told, replacing pin bushings is not a simple job and you are well advised to take your rods to an automotive machine shop. They will likely use a Sunnen hone to size them. Even regular machine shops are often not well equipped to do this type of work.I don't know enough about this subject to debate you, but it seems like if this were the case, VW would supply pre-reamed bushings. Actually I don't know why VW doesn't supply pre-reamed bushings to begin with -- if the wrist pins are all a standard 24mm hardened and ground to such a tight tolerance that heating the pistons to 140F is required to insert the pins, fer gosh sakes distribute 24mm bushings!! But anyway, it just seems odd for VW to sell bushings that can't be installed by a typical VW dealership tech in a typical VW dealership shop. I.e., using an adjustable hand reamer. So I guess what you're trying to tell me is, a straight blade hand reamer cannot hold a tolerance to .0005"? If I need a spiral flute expanding reamer, I need a spiral flute expanding reamer, but as an aside I am a little bit curious what tolerance a straight-blade adjustable reamer can hold.


The 0.994" given by the OP is actually 23.9776mm which is very close to a nominal 24.00mm.
...
I've bet that a VW dealer or mechanic will have the reamer required. Why not get them to do the reaming for you as they will get it right.I don't understand this. If a fixed size 24mm reamer can be used, why ship unreamed bushings? Just ream them to 24mm at the factory. I assume the reason for shipping unreamed bushings is that the wrist pins vary in size so the bushings must be customized to the pins using an adjustable reamer, hone, or other device that can produce various custom sizes to fit the pins.

tylernt
01-01-2011, 02:27 PM
You don't need any measuring equipment, you have the wrist pin.
Just keep taking a bit out and trying the pin.
My thought exactly. :)

ligito
01-01-2011, 02:45 PM
I don't understand this. If a fixed size 24mm reamer can be used, why ship unreamed bushings? Just ream them to 24mm at the factory. I assume the reason for shipping unreamed bushings is that the wrist pins vary in size so the bushings must be customized to the pins using an adjustable reamer, hone, or other device that can produce various custom sizes to fit the pins.


Because wear and reality tend to make things wander a bit.
Let a shop do it for you, it'll be faster, too.

hardtail
01-01-2011, 02:57 PM
You likely can do this.......and you are learning the procedure and challenges for attempting to do so.......I'm sure over 99% would take this to a reputable auto shop and they would be done in a few minutes on a Sunnen machine.....probably way cheaper if you considered your time and setup BUT it doesn't mean you can't.

I would think the bushing might tighten or shrink slightly as it's installed into the rod......but they probably could have supplied them a little closer to size......maybe they supply them this way as the smallest possible to not collapse or deform on the install? Was there any tool you made to press them in? Or others use?

I doubt your DP has the tight tolerances for holding .0005 and John has mentioned the number of cutters can effect the finish but I would think with some careful prep to mount the rod truely perpendicular and finding the true center of the pre machined bushing this could be accomplished, I would probably try and get close with the reamer and hone to finish size......do you have one rod to do or all 4?

Pity I was at a farm auction a couple years back where the guy dwelved into lots of machining and fabrication wheelchair bound and he had the Sunnen machine with lots of arbors that went for little $$$'s, I would have been wise to throw up my hand........

gnm109
01-01-2011, 03:24 PM
You asked for the best method. That would be on a Sunnen Hone. With wrist pins, most anything you do by hand will loosen prematurely.

That said, it can be done, but results may not be certain.

tylernt
01-01-2011, 04:06 PM
Was there any tool you made to press them in? Or others use?I turned a mandrel on my lathe. Actually the mandrel just started the old bushing on it's way out, the new bushing was used to press the rest of the old one out.


I doubt your DP has the tight tolerances for holding .0005 Agreed. What if I centerdrill the end of the reamer and use a dead center in the chuck to press down on it and turn by hand? Would the center negate the runout?


......do you have one rod to do or all 4?4, unfortunately.

Doozer
01-01-2011, 04:18 PM
Yes, a Sunnen hone is the only tool to do the job right. I have used one many times, and to take .0001" is easy. To measure, use gauge pins to sneak up on the size, and use your piston wrist pin for final sizing as you selectively hone the taper out. Any other methods for doing this is just pissing around. How much will it cost you when your new engine has pin knock? Pay a shop with a Sunnen hone to do this. --Doozer

gnm109
01-01-2011, 07:25 PM
Snip....

I don't understand this. If a fixed size 24mm reamer can be used, why ship unreamed bushings? Just ream them to 24mm at the factory. I assume the reason for shipping unreamed bushings is that the wrist pins vary in size so the bushings must be customized to the pins using an adjustable reamer, hone, or other device that can produce various custom sizes to fit the pins.


Yes, of course, wrist pins may very somewhat and that could be a reason but the more likely reason is that the bushings compress a few 10's when pressed into the small end of the connecting rod.

Wrist pns are very critical. I've seen them wear loose in 100 miles when folks used those expandable reamers. The finish is not all that smooth and the pins may fit after reaming yet they wear quickly loose.

rohart
01-01-2011, 08:43 PM
Surely you get the chance to ream them not for the size but for the alignment. If your rod is slightly bent, as long as you ream the little end square, all's fine.

I'm talking from experience with bikes with ally rods, where you don't want to bend the rods straight. I hear you can do that with steel rods.

It would be interesting to hear if the VW engine uses ally rods.

John Stevenson
01-01-2011, 08:54 PM
Wrist pns are very critical. I've seen them wear loose in 100 miles when folks used those expandable reamers. The finish is not all that smooth and the pins may fit after reaming yet they wear quickly loose.

Adjustable reamers are just a tool like any other, if used correctly the job is fine. If not used correctly, don't blame the tool.
Most of our big Rolls and Cummins engines ran 160,000 to 200,000 miles before a pull down.

NzOldun
01-01-2011, 09:08 PM
This is for a DIESEL!!! Presumably with a compression ratio of something like 16:1 and a peak firing pressure of several thousand p.s.i !!

Those wrist pins, if made by VW, will be accurate to ~.00001 or better. They will have been finished on a centre-less grinder and you would need high grade laboratory instruments to detect any diametrical differences. They need to be a light push fit with both piston, con-rod and pin at the same temperature,

The warmth of your hand on the pin should be enough to prevent assembly.

The fit needs to be concentric, smooth and square all the way along the bush. This is absolutely critical. ANY off-squareness, bell mouth, ovality, Sir John's 'threepenny' bit finish or anything which prevents full, even, contact, will significantly reduce the life of the bush-pin joint. Get VW to do the job!

tylernt
01-01-2011, 10:38 PM
It would be interesting to hear if the VW engine uses ally rods.The rods are magnetic, so I assume steel. And if they're bent, you throw them away. ;)

Compression ratio is 23:1 (prechamber design, not direct injection).

oldtiffie
01-01-2011, 11:09 PM
Because wear and reality tend to make things wander a bit.
Let a shop do it for you, it'll be faster, too.

The sleeves/bushes are accurately sized for a compression/interference fit into the snall end of the con-rod in the factory.

The sleeve/bush will distort slightly as it is compressed as it is pressed into the small end of the connecting rod.

Both the small end bore as well as the outside and inside diameters of the sleeve have quite close manufacturing tolerances as individual items. But those tolerances can be all additive, all subtractive, a mix of both and may even be self-canceling. The alignment of the big and small ends must not only be accurately sized but must be very accurately parallel.

A very accurate special machine for reaming/boring and honing is required.

A reamer will normally tend to follow the hole it is reaming and that is why boring is sometimes required pre-reaming/honing.

But despite any advice by others it the OP's call after all as it is his engine.

tylernt
01-01-2011, 11:32 PM
Ok, you guys convinced me... I'm going to try to find a local shop with a Sunnen. I believe many of you here could probably get acceptable results in your home shops, but it's not worth the time/effort for me as a newbie to buy a bunch of tooling and risk blowing up the family car. I guess you could say I've decided I'd rather be safe then sorry in this situation.

I still learned a ton from this thread, though. I appreciate the advice and info from both sides.

The most important lesson of all, though, is if your old wrist pin bushings are still within spec, even barely, don't *&%$^@! mess with them!! :mad:

Don Young
01-01-2011, 11:43 PM
I am concerned that you seem to have only a straight fluted adjustable reamer. I feel pretty certain that the split in the bushing will cause irregular cutting. A lot of piston pin bushings have been reamed, some manufacturers even specify a tolerance for reamed bushings which is somewhat tighter than a honed fit. However, I recall the tolerances to be in the .00015" to .0002" range. This equates to a light thumb push fit with no detectible clearance.

I think you will find that VW dealers either have special reamers and hones for this work or they send it out to an automotive machine shop. These bushings are not supplied pre-reamed because the manufacturers cannot economically hold the needed tolerances that way. Pressing in bushings causes the bore to shrink and the bushing also may slightly distort in other ways.

Since you have spare bushings, I would suggest that you try reaming them. I don't think you can fixture the rod or reamer in any reasonable way to improve the alignment you can get with careful hand work, but it might be worth a try. Just don't assemble the engine unless you are sure you have a good fit and good alignment. Although, as has been mentioned, you do not have to measure the clearance it may be informative to know what VW specifies for clearance and its tolerance.

edit: I just read your previous post andI had been wondering if you had a pin bushing problem when you tore the engine down. I still think you should try one, just to get a first hand idea of what is involved. You can then replace it and get on down to the shop. Good Luck.

boslab
01-02-2011, 01:11 AM
The 1.6TD is an old unit, I think it was the BK series, I dont understand whats happening really as the last time i stripped one i ordered pots and pins and they fitted out of the packet just fine, Ihave another one to do soon as the weather picks up an old Audi 80 with the 1.9td, i'm going to bin that and fit the TDI 120HP instead of 80-90, but anyway, if your determined then the right size spiral reamer with the pot jigged and the reamer in the quill of a vertical spindle milling machine, buckets of coolant and bugger all rpm sounds like a plan!, i dont think i'd go near it with an adjustable unless i really wanted to do the job again in 6 months as punishment, and you cant do it through the sump as the front crossmember is in the way, engine and box out, again, oh what fun. you could fit quick release couplings on all the hoses the amount of times your going to delve in there!
regards
mark

Rustybolt
01-02-2011, 09:26 AM
I believe many of you here could probably get acceptable results in your home shops,


On my lawnmower, or my dodge 318,sue. But not on a modern diesel. Not if you want it to last another 50,000 miles or more.

hardtail
01-02-2011, 12:28 PM
A straight adjustable reamer will work on a split bushing.......I've done it but the odd number of cutters maybe the key.......you have to be patient to sneak up and I honed to finish size......

Yes the compression on those VW diesels is way up there......almost 50% higher than most others.....I'd be concerned with installed deck height.....as another goal......

If your lathe was larger and you had a faceplate you might be able to do it with a boring bar and finish hone.........

JoeBean
01-02-2011, 07:19 PM
I'm trying to rebuild an engine and I installed some new wrist pin bushings in my connecting rods. Only when I went to install the wrist pins did I find that the bushings are shipped deliberately undersized so they can be reamed to fit the wrist pins. Since I have a drill press and mini-lathe, I wondered if there was a way to do this

One thing that worries me is the tolerance of the final bushing ID is .0005" (half a thou), and I'm not sure that I, as a newbie, can hold this tight of a tolerance. My dial calipers are only accurate to .001", for example.


I saw your post over on vwvortex. You're right to be regretting the decision to replace the bushings. As mentioned over there they virtually never go, without other SERIOUS problems being evident (like oil pump failure). I've rebuilt more 1.6 IDIs than I care to remember - at one point I had 2 myself, my parents had one, and I maintained a fleet of 8 more. Only twice have I seen an out of tolerance bushing on these engines, and in one of those cases the engine was so badly damaged as to be unrepairable (within a reasonable budget, ie. for less than another engine). The suggestions are right, they ought to be honed to size if you're going to do it, but if it were me I'd get a full set of conrods from a scrapyard or a parts dealer (if you're in Canada try Autolectra in Momtreal as they usually are way cheaper than anyone else).

It sounds like you don't even have the equipment necessary to have verified they're out of spec. Hard lesson to learn, I know, but always read the manual thoroughly and understand what you're getting into nefore you jump (and not the edited Bentley, the actual VW service microfiche - The Bentley is based on the same info, but is missing some).

tylernt
01-04-2011, 05:09 PM
An update: I found a machine shop and they are only charging me $25 total to put my rods on their Sunnen?! That seems way cheap to me, that's less than the cheapest hand reamer I could find. At that price it must take about 2 minutes labor per rod!


It sounds like you don't even have the equipment necessary to have verified they're out of spec.
True, but don't dial calipers usually read undersize when measuring the ID? Unless my zero was off (which I checked), I don't know how I could have misread the hole as oversize.


Hard lesson to learn, I know, but always read the manual thoroughly and understand what you're getting into nefore you jump (and not the edited Bentley, the actual VW service microfiche - The Bentley is based on the same info, but is missing some).
Yeah the Bentley says nothing of reaming to fit after installing new bushings. In fact a lot of the internal engine rebuilding info is missing from the Mk2 Bentley and only contained in the Mk1 Bentley. :eek: