Valve clearances explained

[Garnet]

http://www.motorcycleproject.com/text/cows-clear.html

[grant81rs]

Gidday

nicely explained

[bbelk]

For the time being - engines without pushrods are not of much interest. Except for my boat and of course my cars - the lawn tractor I am not sure about.

[Zombie Master]

Very good!

[gocytocis]

I'd not spent much time considering how clearances may play a different role in pushrod motors vs OHC/DOHC motors; interesting!

[Duane Ausherman]

That info is just related to some really old engines. For example, it explains what happens to the /2 type. The /5 and later are almost perfectly compensated for heat.

Don't believe me? Good, test it for yourself. As you pull into your garage with a fully /5, /6, or /7 hot engine, remove and check the valve clearances. Let it cool over night and test again in the morning. No change if the engine is any good. If you find more than a thou, you better get ready to spend some money.

OK, who is going to run the test and report back?

We have known this for only 45 years now. This motorcycleproject.com site should be quite ashamed of putting out such info. The info on the ramp design is accurate and good info, but some of the rest is not.

I have no idea if this applies to the "new stuff" such as oil heads and the 3-4 cylinder engines. I have never ridden one, or worked on one and don't intend to start.

[Major Softie]

I have no idea if this applies to the "new stuff" such as oil heads and the 3-4 cylinder engines. I have never ridden one, or worked on one and don't intend to start.

The Oilheads do have pushrods, but the cam is 1/2 way up the cylinder, so the pushrods are very short. If BMW was able to compensate for these issues in the long pushrod motors of the /5, I'm sure they were also able to in the Oilhead.

The other motors you mentioned are not pushrod motors.

[Garnet]

Duane said:

"OK, who is going to run the test and report back?"

I have done that test in the past: There was no change in clearance that I could measure with a feeler gauge on a couple of my /5s.

GSPD was an advocate of setting your valves at any engine temperature, and without use of feeler gauges.

[Duane Ausherman]

One could do it without feeler gauges, but that doesn't take into account the movement of the cam as one takes all slack out of the system. Besides, at a commercial shop one must document, with numbers, such things as drift and torque findings.

One must really push hard on the pushrod to get the slack out and only then does the feeler gauge have an accurate use. I see a lot of people do it poorly and they don't get a good result. The "real" gap can vary while they seem to find it as stable.

[Major Softie]

One could do it without feeler gauges, but that doesn't take into account the movement of the cam as one takes all slack out of the system. Besides, at a commercial shop one must document, with numbers, such things as drift and torque findings.

One must really push hard on the pushrod to get the slack out and only then does the feeler gauge have an accurate use. I see a lot of people do it poorly and they don't get a good result. The "real" gap can vary while they seem to find it as stable.

GSPD's system was to tighten it up snug (zero gap) and then back off a certain number of flats. For some people this probably is much more consistent, because it makes it easy to eliminate the slack you're talking about.