TR7 Cylinder Head dimension?

[Howard722]

My understanding is that the limit for refacing a head is 112.45mm measured from the face to the root of the cam journal diameter.

Does anyone know what this dimension would have been for a new head when newly assembled in the factory-113, 113 .5 ??-there probably would have been some tolerance for good/new head units.

I have a spares stash head that outwardly looks v.good but measures 112.00 so this appears to be over the limit and would probably be a candidate for a thick head gasket assuming its OK as is for re-use ??- (but probably wouldn`t stand another reface!-yes/no?).

As I`ve trawled around for info. I`ve read that refacing the head eventually impinges on valve timing and that redrilling the cam sprocket may be needed or use of an adjustable/vernier cam sprocket(do these exist?), but also this is not needed provided (with no.1 at TDC) the cam timing marks are within 3mm.(which seems generous)-anybody have input on these details?

Any advice, input on this topic much appreciated, especially if this spare head can have a future life with some tweaks along the way.

[Beans]

Another thing to bear in mind is that, due to the angled position of the studs, with excessive skimming the distance between the bolt and stud holes changes.
Probably the reason there is no thicker head gasket listed in the original parts manual.

[Rich K]

As Beans says, the stud to hole clearance will be adversely affected by skimming the head more than a certain amount. Presumably this situation could be remedied by reaming out the holes sufficiently in order to reintroduce sufficient clearance.

[Rich K]

Hi Howard,
there is a thread on the Stag Owners Club forum under the title “Cylinder Head Thickness” that should also be relevant to TR7 heads as I’m pretty certain they are effectively the same as Stag heads. It states that the new head thickness is 112.64mm. The discussion also mentions potential problems with valve to piston clearance and cam timing when a head has been skimmed past the limit of 112.45mm, and the use of thick head gaskets as a solution.
Cheers,
Rich.

[Howard722]

Thanks for the inputs.
I can see how head refacing would have some effect on dimensions with the angled stud holes.
If our heads were indeed the same original thickness as the Stag heads (112.64) then there was never a lot of material available if 112.45 is the min.-I make it less than 0.010."
Stag heads are similar but not the same but they seem to have head shim options as well -do we have anything like this or just the extra thick gasket?

[Rich K]

My understanding is that metal “saver shims” are sometimes used on Stag engines to reintroduce thickness lost by skimming and that these are made from copper, stainless steel or aluminium. These appear to be bonded onto the block using Wellseal or similar. I don’t see why this method couldn’t be employed for TR7 heads, although I am not sure why anyone would go to this trouble when a thick head gasket would presumably achieve a similar result. Perhaps a metal shim is utilised where it has been necessary to remove too much metal for a thick gasket to provide the required regain in thickness.

[Hasbeen]

Does a Stag head go on to a 7 block?

If it does it would be an easy way of gaining a higher compression ratio, with out excessive shaving.

When I was racing Aus F2 we built our own version of the Cosworth 1098cc Ford Anglia engine. We believe Cosworth & & Holbay were supplied cylinder heads with a shallow combustion chamber to allow higher compression with out excessive shaving. to get the same compression with a stock head required shaving to the extent that heads usually warped after not much use. 11.5 to 1 was required to get best power out of the Ford 105E Anglia engine.

To avoid this we had a top welding company fill the combustion chambers with cast iron weld, then carved our own shaped shallower combustion chambers. It was an interesting process. The company spent 2 days slowly heating the products to be welded, did all the welding on Wednesday, then spent another 2 days slowly cooling the welded articles.

This controlled post welding distortion. We were amazed to find the head required only a 15 thou skim to get a fully true, flat face.

Hasbeen

[Howard722]

As I see it there is very little material to take off from a starting point of `new` at 112.64mm. In fact 0.010" (ten thousandths of an inch or ten thou.) takes it down to 112.39mm.-below the 112.45mm limit [ and mixing up metric and imperial dimensions doesn`t help but I think we`re all more at ease with small dimensions being imperial like old school feeler gauges etc.].
Even setting up a head to be level in both planes within ten thou. takes some precision and I note that one of the Stag contributors had a six thou. difference between the ends of one head and I could well believe that`s not unusual.

Ten thou. is a very very thin skim and probably would need to take off more to clean up the whole surface (typically 20-25 thou.) hence the need for the thick gaskets but this begs the question what do you next time the head need attention as option are................hmmm.........?
As we are into 40 years use now do we have some experienced engine fettlers who have some good ideas/advice?

(Just to add .. I don`t think a Stag head will fit to a TR7 block, galleries seem different and the timing chain end is a different shape from what I can see.)

[Cobber]

I seem to remember that a Stag club somewhere (probably the UK, but maybe here in OZ) had the opposite sided head to ours reverse engineered, so I'm guessing that the reason they didn't bother with the other head was that they still considered that there were enough of the other side (our side) available.
Maybe they were just looking into the feasibility of it, I cant remember the details.

[Rich K]

Just found a very helpful article.
https://tscusa.org/tech/Stag%20Engine%2 ... (Top%20End).pdf
This covers a lot of information about rebuilding Stag heads including problems associated with skimming, shims and thicker gaskets etc. Should also be relevant in principle to TR7 heads.

[Howard722]

Thanks for that link.
Some useful insights in there as clearly both engines have similar issues. I note in the article comment about refacing getting close to the valve seat insert being a limiting factor and also a `when new` dimension for the depth of the inlet valve seat (i.e small step) to the head surface of 0.060". -handy for checking.
The Stag boys seem to have a few more tricks with head shims/savershims and time will tell if these options become available for our engines and then we will need to get clued up on shim bonding etc.
Would be good to find/get some feedback from Stag owners on experiences with fitting and using head shims!