Valve lash

[crooked1/2dozen]

Hi y'all:

I had a deja vu last week when I set my rocker lash. Back about 1969-1970, Mr Rouse's auto shop class, there was a slant on a test bed, I had to set the valves on it after they were placed out of adjustment. Holding the 7/16th(?) wrench on a moving rocker....I knew I'd done it before!
But here's a question, I set my Triumph Bonneville lash when cold, .003Int and .005 Ex, lash is taken up as pushrods expand. Why do we set lash when warm, and why so much lash? I remember reading a thread somewhere and the person said if the lash is too small, compression will get too high, this doesn't seem to make sense to me. It would seem to me that if there were only a couple of thou lash when hot, no valves would be held open and wouldn't get burnt, plus with a trace higher lift, breathing would be better. But what do I know!

Someone 'splain this to me!


TIA

Dan

 

[RustyRatRod]

I always set mine not running cold and be done with it.

 

[Valiant50]

Hi y'all:

I had a deja vu last week when I set my rocker lash. Back about 1969-1970, Mr Rouse's auto shop class, there was a slant on a test bed, I had to set the valves on it after they were placed out of adjustment. Holding the 7/16th(?) wrench on a moving rocker....I knew I'd done it before!
But here's a question, I set my Triumph Bonneville lash when cold, .003Int and .005 Ex, lash is taken up as pushrods expand. Why do we set lash when warm, and why so much lash? I remember reading a thread somewhere and the person said if the lash is too small, compression will get too high, this doesn't seem to make sense to me. It would seem to me that if there were only a couple of thou lash when hot, no valves would be held open and wouldn't get burnt, plus with a trace higher lift, breathing would be better. But what do I know!

Someone 'splain this to me!


TIA

Dan

Lash to small compression to high? - nonsense - the opposite might be true - please note might if you a running very high cr and even then it does not make sense as a statement - increasing the lash will decrease your overlap and effective lift - increasing torque BTW - due to an increase in pressure - gas have have less time to escape while piston is moving up and valves are being closed

On a slant you get your most accurate setting setting them hot while idling
I have tried it repeatedly on different slants - and there is no cut an dried cold setting that works

I have a suspicion it has to do with the rockers being oiled under pressure
the oil acting as a hydraulic bearing and thus taking up clearance while under pressure - I know that 273 rockers had to be set this way as well for the best results

 

[slantsixdan]

Someone 'splain this to me!

The explanation is simple: you are working on a slant-6, not on a Triumph or a bathtub or a celery stalk. One might as well ask "Hey! How come I shouldn't use Honda procedures to overhaul a Mopar transmission?". Use the correct procedure for the machine you are repairing. In this case, the procedure is here.

 

[crooked1/2dozen]

The explanation is simple: you are working on a slant-6, not on a Triumph or a bathtub or a celery stalk. One might as well ask "Hey! How come I shouldn't use Honda procedures to overhaul a Mopar transmission?". Use the correct procedure for the machine you are repairing. In this case, the procedure is here.

Thanks for the quick replies.

It's all good, SSD, proper slant procedures followed for adjustment, also, lash not set @ 15/18 when warm on the Trumpet! And, another procedure followed on my other A body, a 1929 Ford phaeton!

I was just wondering why so much lash is required on this particular engine.

Cheers

Dan

 

[slantsixdan]

I was just wondering why so much lash is required on this particular engine.

Shape of the cam lobes.

 

[cudamark]

Thanks for the quick replies.

It's all good, SSD, proper slant procedures followed for adjustment, also, lash not set @ 15/18 when warm on the Trumpet! And, another procedure followed on my other A body, a 1929 Ford phaeton!

I was just wondering why so much lash is required on this particular engine.

Cheers

Dan

Expansion of the various parts plays a part in the tappet clearence also. When I assemble a slant 6 and need to adjust the valves cold before I start it for the first time, I set them .002 looser than the hot setting. Once I get it to full operating temp and have "broken" the engine in a bit, I'll readjust them.