View Full Version : Engine Block Machining Help

11-19-2006, 10:54 AM
OK - I need to tap into the collective wisdom of the group.

A little background first. Just picked up a used straight 6 (2.5L) engine. The thrust washers wore enough that they dropped out and the crank then damaged the block. I've since cleaned up the thrust face on the crank, so that's ok. But it now has .038" of clearance (spec is .006-.008). :eek:

First off I want to clean up the block since the crank wiped out the shoulder the thrust washer is positioned by. The block is too long to stand up in my Bridgeport to get at the thrust washer mounting. It's located on the last (outside) main bearing cap. My thought was to lay the block upside down (head mounting surface - the "deck") on the mill table and rotate the mill's head 90 degrees. I'm then planning on counterboring the block for an adapter to hold the new thrust washers. Any problem with running the J head Bridgeport like that?

Secondly I need to make a carrier / adapter to hold the new thrust washers. It will be round with a lip on the od and an inverted lip on the id (think of a shallow round sink with a drain). It's got to be split to go around the crankshaft and that's what's got me stumped. :confused: I can machine the adapter round and then split it, but then the split faces won't meet. That will be bad news as the oil from the main bearing will leak out through the gap and not be forced past the thrust washers. I could make up two adapters, cut each one off center and finish so the pair will make one complete piece, but that's pretty wastefull. There's got to be a better way!

The only suitable material I've got is a 4" wide x 1/2" thick piece of 410 stainless. Otherwise I've got some 5" 6061T6 round bar, but not sure that will hold up over the long term. The finished adapter needs to be roughly 3.25 od x 2.50 id x .25 thick.

My lathe is a 13x40 with a 3 jaw, 4 jaw, and a faceplate. I generally use carbide inserts, but also have a lantern toolpost and can use hss if that's of any help.


11-19-2006, 11:00 AM
One solution is to silver solder two pieces of stock together edgewise and the machine them to size. When you're done unsolder them.

11-19-2006, 11:10 AM
So far as fixing the block,a boring bar can be fitted up in bushing mounted in the main journal bores,just fit the bar with a Hss cutter that protrudes out far enough to cover the entire face needing to be machined.Crank the bar by hand with a crank and use a bar with a push bolt in the center to apply axial pressure to the cutting tool.Machine it until clean and then calculate the thrust washer thickness.

I have made thrust washers for various engines.It is perfectly okay to machine them up round in the lathe and then split them.Machine a few oil grooves on the thrust side and attach them to the block with four or five small flat head brass screws loctited inplace.There were several engines that used this method from the factory,so long as the endplay is kept to a minimum they will stay in place.

Bronze,either SAE 932 or 953 would be my choice for the bearings,not steel or stainless.Even steel with a babbit coating would be better than steel or stainless,less chance of galling/welding.

11-19-2006, 11:26 AM
Thanks for the input guys.

Rustybolt - I do have some silver solder so that will work out rather well.
Wierd - I'm planning on using new stock thrust washers (new ones are bronze, originals were babbit) and taking up the freeplay in the adapter. I wasn't planning on running the crank on stainless!

I didn't give you the whole scenario of the block / thrust washer setup. It's a pretty inferior design where they only use HALF thrust washers on each side. That's why they wear so fast.

Unfortunately I'm pretty short on material. I'd have to go and buy the bar to make the hand crank cutter from. It'll defientely be more cost effective to use the BP.

A.K. Boomer
11-19-2006, 11:34 AM
I just briefly read this --- the only thing i have to consider is if you have a manual trans or an auto,,, the manual will create much more force on one side of your thrust (pressure plate load) so be sure that this side has a beefy lock tab to keep from spinning out and ruining all your hard work... (and engine)

11-19-2006, 11:56 AM
The engine fits in a Triumph TR6 so it's a manual trans. LOL - TRs are known for heavy clutches. It's heavier than some of the 24' trucks I've driven. :D

This particular engine is a 'Frankenmotor'. It's got bits and pieces from at least 4 different years and 2 different displacements. :eek:

Normally I would have taken my lumps on a motor like this and just stripped it out for the good parts and scrap the rest. BUT this block shows no bore wear and the crank was freshly reground before the thrust washer incident. Hey, so what if all it takes is a few days of effort to put it right? That'll get me a good relatively inexpensive replacement for the original very tired engine in my '71.

11-19-2006, 12:25 PM
Hi Tom,

Funny, the moment I read your 1st post I was already thinking of a response, knowing that it had to be a TR-6 motor. I fixed a bunch of 'em when I was working for the local British Leyland (or was it Jaguar-Rover-Triumph in the 70's) dealer. The 1st thing we looked for when pulling the 12-24-30K (mile)interval maintenances was a stiff clutch and would try to upsell a clutch job. We would tell the customers "Pay me now for a nice, new easy-to-push clutch or pay me later for a much more expensive clutch AND thrust washer job." They always thought we were trying to hornswoggle 'em. Inevitably, they got towed back in on the hook.

If they noticed the dramatic change in clutch feel and the idle drop that came when you depressed the clutch and pushed the crank and rods forward...and had it towed quickly, we could fix it by dropping the pan, slipping in new thrust washers and drilling & tapping the lower main cap for a couple of carefully fitted socket-head capscrews to hold the washers in. Otherwise we fitted a new shortblock.

Speaking of TR-6's, have you already boxed in the diff mounting stud brackets? They ALL broke. How 'bout the snap ring at the front of the gearbox mainshaft, next to 3rd gear? Has it jumped off yet?

Funniest TR-6 story is about the customer that tried to drive through about 2 feet off standing water. He just revved 'er up to 3000 rpm to keep it running. The crankshaft mounted plastic fan blade (low!) tried to make like a boat propeller and screwed itself right into the radiator. He said there was this funny sound under the hood and then it overheated a few blocks later. Tried to claim it as a warranty repair!

Ahh, for the good 'ol days.:)

A.K. Boomer
11-19-2006, 12:38 PM
Should have known it was british,,, good god i hope this thing at least has a ball bearing throw out bearing instead of one of those graphite blocks that depress an already drag ass pressure plate, Worked on everything from around the globe -- cars and motorcycles, God the britts had some absolute crap,,, I hope sir john doesnt take offence to this because then i will have to tell him where he can fit his "stromburg carburators" - All in good fun;)

11-19-2006, 01:54 PM
Nope, TR-6 has a ball-bearing release bearing.

The carbon bearing actually was a pretty decent idea in early British cars. It wore at approx. the same rate as the disc and was self adjusting.:) Early Beetles had the same thing so don't make fun of just the British.

Actually the British were way ahead of their time. They built cars that put the oil back in the ground where it belongs! ;) :D

11-19-2006, 06:10 PM
Hi ****eybird,

BL was from 69 to 78/79/80 I think. JRT was after that.

This one is a California car that my son and I picked up in San Jose in May and drove it home (Chicago) visiting 6 national parks along the way. Absolutely awesome trip. Alot has been done to it over the years (good and bad) but overall not really abused, just well used. No rust at all and very solid. Hell, even the frame is still painted black just as it left the factory 35 years and 150k miles ago (or maybe 250k - don't know).

The stud brackets are still factory and not yet broken (I've checked). Although with the way I drive they probably won't last much longer! :D Trans is ok so far, but will be changing that out for the later J type box with overdrive once the 'new' engine gets sorted.

Boomer - Well what can I say - I like the "absolute crap" that the Brits put out in years past. Not for everyone but then again following the herd is not my thing. All in all for me the TR6 is just for fun. My daily driver for the last couple of years has been a '78 MGB (there's that Brit thing again). Good solid car and fun to drive. Really fun to drive now that it's got the supercharger on it! :D

The MG uses the graphite bearing and it works remarkably well. You just shouldn't hold the clutch in while sitting at a light. Treated right it will last for a couple of clutch jobs.

Oh, and my cars don't leak - they mark their territory!

C'mon guys, no advice on tilting the head of the BP?

11-19-2006, 09:56 PM
I have enjoyed this thread chuckling at most of the posts.

Ausserdog, have you considered boring the block as you planed but bolting up the main cap and boring both and making a thrust washer that would fit in the recess and provide more wear surface? You could make the thrust washer out of Ammco bronze, it's an aluminum brass alloy I think. Anyway we used it for wear plates on machines. Mighty tough stuff.

Yes, you can lay the head over on a bridgeport type mill for short jobs and a boring head would do the job. Just be sure to support the block so it don't tip the mill over:eek: :D .

Spin Doctor
11-20-2006, 09:06 AM
As far as tilting the head goes. You can do it but it is gonna be a cast iron witch lining everything up straight. Another option is to set up the block in the lathe and use the lathe as a horizontal boring mill. If this got mentioned sorry, I got lost in the humor about British sports cars. That's why I like the Miata. It's everything the British Sports Cars should of been and nothing they are.

11-20-2006, 10:11 AM
Carld - I've long gotten used to the ribbing I get for driving such an 'old, unreliable little car' and when will I get a 'real' car. Funny thing is the last guy that told me that had to do a $1600 trans job on his 'reliable' 5 year old American car a month later. :rolleyes:

Here's the plan. I've got the bearing cap bolted in and will counterbore it and the block at the same time. Once that's done the crank will get dropped back in along with a pair of stock thrust washers. Measuring the crank float will tell me how thick to make the thrust washer carrier. Originally there were only 2 half thrust washers - one half on each side. It will get 2 full stock thrust washers (4 halves) when done. The ones in the bottom cap will get pinned to keep them all from rotating. Figure it'll help keep the oil flowing between the crank and thrust washers creating a hydrodynamic bearing. Something the original design didn't take advantage of.

Surprised the heck out of me putting the block on the table. For a 6 cylinder it is light - I think the MG 4 cylinder block is heavier. Not sure if that's good or bad just know that my back is thankfull!

Spin - I've already got the head trammed to the table. Took a while but it was the first time I've had to do that. Getting the block aligned won't be too bad since I can indicate off of the side surfaces that locate the main bearing caps.

I did think about using the lathe, but the saddle is way too small and accuracy would have been questionable.

The Miata is a very nice car. The head designer of the Miata project (don't remember his name) is a big time MG fan. He approaced it as a successor to the car keeping many of it's better attributes.

A.K. Boomer
11-20-2006, 12:54 PM
Surprised the heck out of me putting the block on the table. For a 6 cylinder it is light - I think the MG 4 cylinder block is heavier. Not sure if that's good or bad just know that my back is thankfull!


I cant believe what i did as a young man, I built up a BWM 1600-2 engine in my upstairs apartment, got it all done and no-one was around to help so i carried it down two flights of stairs to install it in the car, i remember the apartment stairs flexing a great deal with every step, it was scary, those were the days fella's...