Milling Question

[aboard_epsilon]

ummmmm
maybe a snag to some people ...
but its a challenge to me .
a Triumph Stag engine requires looking after , maintaining ..and a good understanding of it's failures ...and how to correct them
if you know and understand it ......then they are just as capable as any other engine.
the rewards of ownership for me outweigh anything else.
mmmmmm do I nead to say anymore.
all the best.mark

[BillH]

Take a look down near the bottom, he used the grinding disk method with a miniature mill.
http://www.saunalahti.fi/animato/3003/3003x.html

[aboard_epsilon]

My stag.
its the only photo i have of it ..looks even better from the front and with the top down.



all the best.mark

[PaulG]

Before you surface that head, you better make sure the cam turns freely. Those heads (and TR-7's) were notorious for twisting when they overheated. To avoid cam bearing problems, the best thing was to not surface them (assuming they were not pitted) and put them back on that way.

[Dave Opincarne]

I had no problem lapping the head of my 22R flat on a surface plate using several sheets of sandpaper and spray glue. If you have to move it from the table I'd clamp it to a fixture plate of some sort with the middle of the head being cut at the end of the first pass/table movement then spin the head end for end without moving the table this time starting where you left off and bringing the cutter into contact using a paper feeler or layout fluid to kiss off with. This won't guarantee a flat head but if it doesn't come out flat it's better to have a gentle bow of one or two thou than a sudden step.

Of greater concern would be making sure there's no bow in the saddle.

Dave

[aboard_epsilon]

As far as I know non of my heads is warped.
they are still in place on the three engines I have.
I have 5 to do...that's if they nead doing.
Over the years I have accumulated three complete engines for spares.....
these were all runners .......what I want to do is to have everything servicable ..the best bits go to make a complete engine .....and out comes the rover 3.5 v8 thats in it at the moment.
the rover was a good runner ......but got sick of people saying its not right unless it has the right motor in it ...A TRIUMPH 3 LITRE V8 ..so I thought ..what the hell.....lets see if I can build one , but make a few modifications to the way its cooled....and enjoy solving a few problems as I go along.
with luck I should be able to achieve this .
all the best.mark
btw if the head is twisted they recomend line boring the cam journals.
all the best...mark

[This message has been edited by aboard_epsilon (edited 12-31-2004).]

[PolskiFran]

A few weeks ago I milled a 4deg. 8min.angle on CRS bars 36" long. I did not have enough travel in the mill so I moved the part along stops that were keyed in the T slot. When the travel ran out, I lowered the table .100. Moved the part. Cranked the table back up. Watched as the cutter made contact with the part. The table graduation dial was .0005 off of the original zero. Continued cut to finish the part. You could bearly see where the cut stopped and started. Of course one pass through is better if you can do it.

Frank

[PaulG]

Mark,

Certainly line boring the cam journals and surfacing is the best fix. But in the "old" days, I replaced dozens and dozens of head gaskets on Stag/TR-7's without either and never had a gasket go bad that wasn't from another overheat session.

[aboard_epsilon]

PAUL.what you're saying then,is that if a head is warped , it will twist back strait when you tighten it back down.
Not heard any stag owner take that aproach before, usualy the overheat sesions are brought on after loosing water from inlet manifold gaskets or heads......they can start weeping unseen over a long period.
once the water drops down ,an inch or so the water pump is then pumping air .......it cavitates and so on to overheating.
the extra pressure of it running hot... 20psi can also cause hoses to leak.
then if you have any sort of a leak,the system header system will not work.
its one of the most stupid ideas ive ever seen
consisting of an expansion bottle that is below everything....once you have a leak ..the water just stays in the expansion bottle and does not return.
this will be the first thing I modify .....I will put a proper header/expansion tank above the highest water leval point.
All the best..mark

[pistonskirt]

Mark
I think the old adage applies here "if it aint broke dont fix it"
If the heads & block are flat when checked on a surface plate then carefull blocking with wet & dry will give the gasket its best chance, if the gaskets are coated metal laminates then 360 grit & parrafin will give the best key on alluminium, fibre composite gaskets may benefit from a slightly coarser grit, just aim to achieve a nice consistent cross hatched pattern across the faces.

If the "expansion bottle" you refer to is a none pressurised water recovery tank then it can be mounted anywhere convenient in the engine bay, it does not have to be above the engines water level as long as the hose connects to a point on the radiator pressure cap neck just above the spring loaded seal & to the bottom of the recovery tank.
If it is in fact a header tank and therefore pressurised its upper level must be above the engine water level to function reliably.

Oh....and I would certainly not try fly cutting heads without enough table travel to clear the back cut, if machining proves necessary look for a local firm doing machine lapping, it is usually relatively inexpensive & offers the additional benefit of requiring no clamping loads which can distort fragile castings. Be sure to prep the faces as described above after lapping to provide a key to deter gasket slippage.

regards

Brian

[This message has been edited by pistonskirt (edited 01-02-2005).]

[PaulG]

Mark,

"what you're saying then,is that if a head is warped , it will twist back strait when you tighten it back down."

Yes that's what it will do. I have seen lots of these that the cam locked up after removing the head. Then you either have to surface and line bore or just clean up the surface and reinstall. After torquing, the cam will free up. But your right, those engines were easy to over heat and didn't tolerate it well.

[jstinem]

If the head is Al. then don't mill it unless it's scratched or scared. The bolts will pull it down.
Then an Al. head overheats the head expands more than the steel bolts can and strechs the bolts a little. This is what blows the head gasket when cold engine is restarted. If re-torque the head bolts before restarting the engine you will find some of them will loose by as much a 1/2 a turn. Re-torqueing will save the head gasket.

[aboard_epsilon]

Paul I think your right.
I agree with you 100 %
but just to ster things up a bit ,
I'm going to ask about this twisted head being pulled back strait again in:-

http://www.triumphstag.net/start/index.htm

I'm not going to mention your name
I'm just going to say "a seasoned mechanic friend of mine who's worked on many a triumph motor says that...."

it's going to be very interesting seeing what replies I get...looking forward to this will post in a few hours time....that's if it's ok by you Paul.

all the best.mark

[aboard_epsilon]

WELL PAUL
.the main man agreed with you
here's his reply:-
Hi Mark

>He found that,by just chucking in a new gasket and tightening the head
>that everything was pulled back into the correct shape again...the
head
>straitened out and the camshaft became loose again.

This is so and I have mentioned it a number of times on the list.

Many repairers automatically go into "weld and skim the head" mode
immediately they see a Stag (or TR7 etc) head with a bit of warp or
corrosion - this is not only a waste of time/money, but potentially
reduces
good heads to scrap.

The "skimmed" head is then bolted up, the cams only turn under extreme
friction, and you have a recipe for damaged cam journals, a broken cam
and/or broken chain. I've seen this quite a few
times.........................

IMHO - Mike Wattam
Chairman - Triumph Stag Register
www.tristagreg.org