The Triumph Dolomite Club - Discussion Forum

I was talking to Steve, one of the 'S's in S&S Preparations, t'other day, and he's/they are the source of the information that the Sprint head will fit over TR7 pistons, despite the cutouts being in the wrong place. Apearantly, they assembled one and put a camera down the plug holes to see if there was plenty of clearance, and there was; so they ran it and it works. Obviously this is just hearsay, but I'd trust Steve to tell it true.

If your thinking about it, and want more confidence, S&S are on 01706 874874. I'm sure they'll be glad to sell you the same gasket and other bits as they used.

Graham.

These guys know their onions with the TR7 so I would trust them at their word. They're handy for the stuff which overlaps with the TR7 but their technical expertise is what really counts.

Well I can tell you they are wrong.
Why, because I rebuilt an engine that was originally built by a well known company and it was a bit of a "PUZZLE" why it failed on several things done wrong but one of these was fitting TR7 pistons in a sprint.
The tops of the pistons bore a witness to being kissed by the valves probably on high revs.
Just a wee skim of the head or an over rev and bang clatter engine gone!

I made a jig to hold the pistons while I cut some notches in the crowns so that they could be used. I have the jig and will modify pistons if the right beer vouchers are handed over.

What about if they used the thicker head gasket or would that still not be enough clearance? Not sure how thick those are.

We've had this before and you are both right cos it depends on what sort of TR7 pistons you use.

If you use the full fat UK spec then they touch. If you use the commonly available US spec with the lower compression
ratio then they clear.

James (knightrider) built up an engine on TR7 pistons (full fat iirc) and he used it successfully until it ingested a K+N securing
nut and he threw a hissy (understandable I guess) and stuck a nissan engine in it.

Jonners

I seem to remember a certain John Priestly in Hayes used to do a conversion fitting a sprint head and the associated timing gear for TR7 owners

I can confirm it does work, but cannot vouch for it in all circumstances.
Jonners can confirm, I bought a supposed good Sprint engine that turned out to have all kinds of other issues but it had "normal" TR7 pistons that had not caused any of the problems, and no signs of contact with the valves.
I wouldn't build one like that myself though.

Jon Tilson wrote:We've had this before and you are both right cos it depends on what sort of TR7 pistons you use.

I'll be speaking to Steve in the next day or two, and I'll ask him about all these points.

But, I do wonder if the head where the valves were kissing the pistons had already been skimed a bit?

Graham

Well you may be right about the head skimming.

It would appear that if you fit the head with no gasket and turn it carefully by hand if it does not touch you have a winner.

Just remember that on peak revs the pistons will go that little bit further than normal which would explain the very slight but notable witness marks in the crowns of the engine that I rebuilt.

I dont like guesswork.

IIRC James had cutouts made in his TR7 pistons to suite.



Jonners

A skimmed head or thin gasket will retard the valve timing a couple of degrees so maybe those getting away with it are just missing the contact point of the valve/piston. If valve timing was corrected due to skimming maybe these are the ones that hit?

Tony