The Triumph Dolomite Club - Discussion Forum

Just reminder - head rebuilt, line bored and skimmed top and bottom - clearance 10 ish on the inlets and 8 ish on the Exhausts..

Got the timing cover off - stuck a protractor on the crank and checked TDC with dial gauge. All good. Retarded cam one tooth and also put one of the ex valves back to correct 18 thou clearance.

Used dial gauge to check ex valve close position on the .18 valve - got 14 degrees ATDC which is near as the book as youll prob get and certinly better than the 35 degrees i started with. Then checked position on the crank on the .08 ex valve which gave 55 degrees.. very odd.

I must be missing something here. Do the tight clearance make that much difference to the cam timing? Nothing seems to fit the book.. do i screw it back together and fire it up and see how it runs or get the head put back to stock tolerances?

When taking readings was the crank rotated clockwise only? Going back would give wrong numbers. Was the cam a tooth out then or have you retarded it just to try it?

Tony

All the readings were taken going clockwise. All the timing marks lined up perfectly before i started, so i was really just seeing if retarding the cam would improve the valve timing.. it did on the valve that i re-shimmed to .18, so this leads me to conclude that because all the clearances are too tight the timing is off. that or i am about 3 teeth out and need to move it some more.

not getting any valve in the new retard position, which is good.

It just all points at the valve clearances to me..

Have you checked the position of the rotor arm at tdc?
Possible that the jackshaft sprocket is a tooth out?

red&black wrote: ↑Wed Sep 26, 2018 2:50 pm Have you checked the position of the rotor arm at tdc?
Possible that the jackshaft sprocket is a tooth out?

Yes this aligns with no1. good there i think.

UPDATE:

Problem solved. Re-shimmed head to 18 thou. stuck it back on and she starts first tickle and runs nice and smoothly.

My conclusion is that reducing the gap from 18 thou altered the timing signifcantly enough to cause rough running.

Problem solved.. Next problem!

philwesty21 wrote: ↑Sat Oct 06, 2018 3:39 pm UPDATE:

Problem solved. Re-shimmed head to 18 thou. stuck it back on and she starts first tickle and runs nice and smoothly.

My conclusion is that reducing the gap from 18 thou altered the timing signifcantly enough to cause rough running.

Problem solved.. Next problem!

Not a problem solved but a problem hidden or accendentally the cam now timed ok when refitting. Changing the valve play that little amount does not cause any difference in running. It only gives a quieter engine.

Jeroen

soe8m wrote: ↑Sun Oct 07, 2018 6:21 pm

philwesty21 wrote: ↑Sat Oct 06, 2018 3:39 pm UPDATE:

Problem solved. Re-shimmed head to 18 thou. stuck it back on and she starts first tickle and runs nice and smoothly.

My conclusion is that reducing the gap from 18 thou altered the timing signifcantly enough to cause rough running.

Problem solved.. Next problem!

Not a problem solved but a problem hidden or accendentally the cam now timed ok when refitting. Changing the valve play that little amount does not cause any difference in running. It only gives a quieter engine.

Jeroen

I agree, I have set clearances at .008" in and .011 ex for years on my own car and for many other Sprint engines for other folk and never had a problem. Indeed I drove a Sprint that I built the engine on only this year at Castle Combe with again no faults. Tighter clearances have no bearing on rough running unless they were set so tight there was in fact no clearance!