The Triumph Dolomite Club - Discussion Forum

I am in the process of rebuilding a cylinder head for my Sprint. I have what I think is a good head to replace my existing one. The existing one has a lot of slop in the cam bucket bores which make a bit of a noise!

It has been skimmed in the past and is sitting right at the minimum thickness of 4.745"

My question is what head gasket do I go for? Do I stick with a standard thickness Payen gasket or is there a "thicker" gasket as there is for the Stag? In an Ideal world I would like to get a few though skimmed off just to clean up the face - though I h=think it would be OK as it is.

Thanks

Roger

Hi Roger,

At minimum thickness you should be OK with a standard gasket.

Beware modern Payen as unfortunately the name no longer means what it used to. A member in New Zealand recently had the issue of his pistons interfering with the fire rings on a modern Payen branded gasket as the tolerances were so slack it had moved on the stud holes and the fire rings were no longer co-axial to the bores! If you can source new old stock then that is your best option; there was a seller on ebay recently with some NOS BL gaskets for about £25.

If you are forced to skim, and personally I'd only do so if it is necessary, then thicker gaskets are available from Rimmers, but I have no experience of their provenance. The 'modern way' seems to be "head off? skim it whilst you have opportunity to do so" but on older cars it's not something I subscribe to unless there is demonstrable flatness issues.

Thanks Alun. I have just looked at the head again and think I agree with you and not skim any more. It is flat and unmarked so not really needed.

Will look out for good quality standard gasket. Thanks for the heads up on potential issues with Payen gaskets, I have come across issues with other "new" Payen gaskets - shame you can't trust a "name" anymore, just like issues with "green box" Lucas stuff.

Roger

The Chinese Lucas parts are in red/black boxes again. So explain you have to have the nos parts in the red boxes but not those in the red boxes. These Chinese hear everything..

As for skimming the head A sprint benefits from a good skim in power and torque wise but before fitting the head I alway's fit the head without gasket on the engine. As for the angled studs/holes, the more you skim, the closer the boltholes become in the head face. Is the engine deck skimmed once or production wise skimmed more than others the stud/bolt holes become wider from eachother and sometimes it can be that these don't match anymore. It's easily solved but knowing the head touches the deck without gasket does make you sure you don't torque the head on the studs but actually are tightening the head on the engine.

Timing is crucial and a few degrees off is a loss off efficiency/power. Skimming the head makes the gears come closer to eachother and sometimes the gears are just inbetween theeth on the mark when the chain is fitted. Then the cheapest option is to redrill the camsprocket 90 degrees rotated to have the camshaft timing exact again.

Jeroen

Jeroen, what size drill do you use to open up the stud holes?

Cheers

Tony

tony g wrote: Jeroen, what size drill do you use to open up the stud holes?

Cheers

Tony

Till it fits. For the Sprints I have dowels in the head/engineblock.

Drill as small as possible. There are different hole sizes in early and late heads. I did buy 100 years ago a sprintparts uprated stud set and these wouldn't go through the holes at all. Looking at some heads to diagnose early and late heads have different size bores for the studs/bolts.

It's also not needed to drill completely through. Start from the face side and take away the minimum.

Jeroen

I think a lot of people take the head off and automatically assume it needs skimming, errr because while its off, why not?

I would advocate checking the heads (and block) with a known straight edge, and if the deviation from flat is only minor, dress the surface with abrasive paper glued to a flat surface such as an old granite worktop offcut or a section of cut float glass.

soe8m wrote: ↑Thu Sep 02, 2021 5:00 pm

tony g wrote: Jeroen, what size drill do you use to open up the stud holes?

Cheers

Tony

Till it fits. For the Sprints I have dowels in the head/engineblock.

Drill as small as possible. There are different hole sizes in early and late heads. I did buy 100 years ago a sprintparts uprated stud set and these wouldn't go through the holes at all. Looking at some heads to diagnose early and late heads have different size bores for the studs/bolts.

It's also not needed to drill completely through. Start from the face side and take away the minimum.



Jeroen

Yes I did think only part way needs to be drilled. I have one head that just makes the studs tight to turn when the bolts are in. Ill take a little out and try it.
Cheers