Calculation of head gasket thickness.

[peterrc]

Hi Guy's, I am in the process of ordering up new head gaskets for my engine and would appreciate it if you could confirm my calculations.
I have measured the head thickness at both ends (the bottom of the camshaft bearing (half bore) and the face of the head). There is a discrepancy between front and back, rear being the thinnest end in both cases and that is the measurement I have used for my calculations.

LH Head thickness 4.412"
As this is below the minimum 4.427" do I need just a saver shim or a standard shim plus a saver shim?

RH Head thickness 4.422"
As this is .005" below the minimum I believe that I need just a thicker gasket. Am I correct.

I believe that Tony Hart did sell saver shims but I cannot see them in his e-bay shop.
Would greatly appreciate confirmation or otherwise.
Regards
Peter, Cupar

[dasadrew]

From a previous post of mine

I can't remember exactly where I got some of this stuff from, but I copied it into my personal Stag Data Log (!) a year or so ago. Might be of help.

Drew

Head Skimming (copied from somewhere)
In order to determine by how mich the heads have been skimmed, the head height between the bottom of the camshaft bearing (half bore) and the face of the head should be measured. A new head is 112.64mm, the specified minimum is 112.40 (obviously, not much skimming allowed). Any amount of skim below 112.40 should be compensated by thicker gasket(s) which add 0.5mm or, if still not sufficient, by addition of a shim (Tony Hart sells "Savershim" which works very well, in my case). A combination of standard gasket on one head (not overskimmed) and thick gasket on the other (if overskimmed) can also be used.
Other sources from Triumph (tech reprints) say minimum is 4,427" = 112,45mm
My Head before skimming = 112,45 mm = exactly the minimum
10thou = 0,254mm
Thick gaskets are 20thou thicker = 0,508 mm thicker

My measurements:

My RH Head after skimming
RH Front 112,00 mm = 0,45 mm under minimum
RH Rear 112,15 mm = 0,30 mm under minimum
With Thick Payens, my RH head is then effectively:
RH Front 112,00 + 0,508 = 112,508
RH Rear 112,15 + 0,508 = 112,658
My LH Head after skimming
LH Front 112,05 mm = 0,40 mm under minimum
LH Rear 112,15 mm = 0,30 mm under minimum
With Thick Payens, my LH head is then effectively:
LH Front 112,05 + 0,508 = 112,558
LH Rear 112,15 + 0,508 = 112,658

[peterrc]

Thanks Drew, that was the information that I used. I was hoping that someone would confirm my calculations before I, spend money and, order up the parts. It's a Scottish thing.
Peter, Cupar

[dasadrew]

... It's a Scottish thing.
Peter, Cupar

What? Even for a Southerner like yourself? Drew (ex-Torphins)

Scottish wisdom.jpg

[DJT]

I've just picked up 2 pairs of Stag heads from the machine shop having had minimal skimming done to clean them up. The ones which came off my engine have measured up as follows:

RH 4.408" or 111.98mm
LH 4.395" or 111.64mm

Another pair I have are:

RH 4.440" or 112.79mm
LH 4.443" or 112.86mm

These measurements call into question the accuracy of the 'new' measurements in the information above. But knowing what BL QAQC was like that doesn't surprise me.

With the best 2 heads the inlet valves are below the head surface by at least 15 thou' when closed, so will standard gaskets be suitable?

Problem is, where do I get some standard Payen gaskets?

[flying farmer]

I have used standard thickness gaskets with valves 5 thou above the head surface with no problems, never even bothered measuring the depth of the head. You will be struggling to find any standard thickness payen gaskets these days.

I bought 3 sets when I found out Payen were not making them any more. Some of the standard thickness gaskets out there are truly appalling, I had a set that didn't compress the fire ring sufficiently to keep the water in the engine, hence the hording of the Payen ones.

I think the 20 thou extra thick gaskets are more or less all you can get now, and should do the job in most instances without saver shims.

The main thing to look out for with skimmed heads is the cam timing, it retards as the head gets closer to the crank, and may need the cam sprocket holes re drilling to correct it, but not always which means it wouldn't have been correct with no skimming!

You know when things are getting marginal when you have to extend the adjustment slot on the chain guides to set the chain tension correct.

Neil

[DJT]

Thanks Neil. I've tried all the usual outlets without success. I'm reluctant to use extra thick ones unless necessary, but that would be better than fitting substandard standard gaskets. I may have found a source, courtesy of this forum, but we'll see what transpires.

[f100stepside]

Hi as you all know by now i know nothing but am learning fast. Guy i spoke to today from Coventry said and he has'nt seen them,' they will need skiming,have they been skimined before (don't think so) and then he will order thicker gaskets to suit from wherever they are available. Asked him what type, and he said depends how much i have to take off. Jonathon

[Ian Durrant]

I swear some machine shops skim them because its easier than properly cleaning off the old gasket lacquer. I'd be suspicious of anyone using the cheap gaskets the main suppliers sell. I have had similar to Neil where the fire rings were so badly made that even after torquing down I could get a 10 thou feeler gauge between head and and gasket with ease, it would have bee a disaster had I fitted the engine without spotting it. If that is the level of quality control then I have doubts about other critical areas of the gasket manufacture.

[Davenott]

Does anyone have any experience with the Cometic head gaskets, that Tony Hart was selling last year?
Dave.

[edd]

Does anyone have any experience with the Cometic head gaskets, that Tony Hart was selling last year?
Dave.

I did see a standard payan set a couple of weeks ago , it looks like the cometic are still for sale

http://www.ebay.co.uk/itm/Triumph-St...item51c4868fcc

[Paul Goldsmith]

With an imminent head work myself, I also curious about these Cometic gaskets - not cheap but if they're the 'nuts' then that could equate to good value. Omens look good, the provenence of TH, modern construction & crucially blanking off the block blind waterways.