G5 Pushrod adjustment

[starfield181]

Investigating my top end oil leak I may also have found the cause of the popping and banging on the overrun. With the engine cold, the inlet pushrod will turn though is a bit tighter than I remember setting it with a warm engine. The exhaust pushrod is very tight and is almost certainly not allowing the exhaust valve to close fully.

Obviously, I can sort this out once I have the bike back together, but I am curious about the setting procedure. If the pushrod clearance is set correctly with a warm engine, will the pushrods be slacker or tighter when the engine is cold? Likewise does the clearance get slacker when its hot or stay the same? Anyone know the answer to this one.
Thanks

PeterF

[SPRIDDLER]

A 'Nil' gap (but pushrod can 'spin') is required on a warm engine. It would seem unlikely that the 'Nil' gap would result in a 'negative' gap (i.e. holding the valve open), when th'engine is hot.

Information from the Web:
The linear expansion coefficient for aluminium alloys (pushrod) is about two times the value of steel and cast iron (cylinder barrel)

Which would suggest that the pushrod, being of greater length than the cylinder, would expand more than the cylinder, holding the valve open.

(Why did you have to start this? )

[robcurrie]

The pushrods do not see as much heat as the barrel, cylinder head and valve gear.

Rob C

[starfield181]

The pushrods do not see as much heat as the barrel, cylinder head and valve gear.

I guess that has to be the answer, nothing else makes much sense. However, I would still like to know how pushrod clearances differ between warm and cold. I set mine cold to 'just free to rotate' whilst reassembling it last night - not much other choice really at that point. I'll take it for a test run today and then check them again with a warm engine.

Does of course beg the question of what exactly is a warm engine.

Peter

[Ozmadman]

I set mine when then engine has been run for a few minutes and warm enough to keep your hand on the cylinder head/rocker cover. The gap must get bigger when hot as you can hear my tappets when hot but they are pretty silent when cold.

[starfield181]

Took the G5 for a test run about 2 miles round the block and it is a much sweeter bike, only one slight pop on the overrun. When i got back I left the bike to cool down long enough to make a cup of tea by which time the engine was about how Paul described in terms of heat. Though they had both been free to rotate when cold, both now needed a bit more slackening off. The inlet being slightly tighter than the exhaust this time.

So there you have it, pushrods cannot be set cold, you have to do it by the book. Oh and there was no sign of oil weepage from the rocker box area so maybe I have fixed two problems. If you ignore the fact that I probably created them in the first place.

Now maybe I can get on with the other jobs.

PeterF