Science Behind Tight Valve Clearances?

Difficult/rough cold starting is classic symptom of no valve clearance (my son running an old ZX6 on a tight budget was once told by his MOT tester "you can't afford a valve check on that - you'll be fine until it starts being difficult to start").
Many years ago I had starting problems on a T595 SprintST with <30k mls, exhaust valves had zero clearance - so much for the recent dealer valve service! Do my own checks since then.
Seeing there's no obvious oil/water contamination personally I'd fix the valve clearances, if a compression test is ok I'd leave the head gasket alone and try running it first (don't fix it if it ain't broke).
BTW more recently I've checked clearances on three different (newish) Triumphs, all of them have had exhaust clearances near/at maximum so I guess the factory aim for that end of the tolerance from new (inlets less so).

 

This is an interesting one, l checked the clearances on mine at the recommended 12000 miles and they were all within limits.
It is quite a faff to do the job though.
Someone told me that all the dealers do is a simple compression test and if that is OK they do not bother to remove the cover and check the actual clearances.
Anyone know if this is true?

 

12,000 miles is sod all really admittedly the first check on a new motor is a good idea simply because if the clearances where tight from the factory then its a possibility that there could be a closing up of the clearances during the initial settling in period, but unless there is something not right to start valve clearances should not change much at all i have seen plenty of car engines with the valve clearances within spec at 60 to100,000 miles and never been re shimmed.

 

Yes, my car has the same bucket and shim principle and there is no requirement at all to check clearances for the life of the vehicle!

 

I would think most cars have hydraulic lifters these days, so self adjusting. I think we don't see them on motorcycles as they are mostly higher performance (and generally lower mileage per year).
I have experience where it was almost certain that valve check was not done when it should (ref my post#21), I doubt this is an isolated case.

 

Incorrect as its the other way around high performance engines use bucket and shims or even just sized buckets to avoid shim spitting at higher RPMs hydraulic are not used on high performance high revving engines because they are hydraulic and cant keep consistent pressure.

 

Well that's what I thought, must be hydraulic,but looking at the workshop manual it appears that they are not, it was the same with my old Nissan qashqai.
From what I gather hydraulic "tappets" are a bit out of vogue nowadays.

 

It's always inlets worse o triumphs. Hardly ever seen problems with exhaust. Some far worse than others. If shims drop below 2.50 it a rapid slippery slope to new valves (non left now). Never seen a problem with seats only the valves.

 

Eager to know more, Stuart, or are you still on that looong night shift?
Ken.

 

Hi Stu;
Thanks for reporting back.
Mixed feeling here about screw extractors....
Hope you are successful with any that need the treatment.
Wish you and yours a great & Healthy 2021.
Cheers,Ken.