Acceptable cam lift tolerance?

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batrider

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I purchased a 1" dial indicator and magnetic base from Harbor Freight on sale and was playing with it this morning. The numbers agree pretty closely with other better quality measuring devices I have (a couple old Starrett micrometers that my grandfather had and good digital vernier calipers) so it isn't really all that terrible, just cheap.

Anyway, I decided to measure cam lift. The head is off right now. For a Combat the manual says .346" exhaust and .390" intake. I'm getting .344" and .386" on the left side and .339" and .388" on the right. I took the lowest reading and made that my zero and then took the highest reading as the lift. I measured each lobe several times and repeatability was good.

Now I'm wondering how close the cams were to the written specs when new. If the cam was originally case hardened then it makes me worry a little about the .339" lobe. The bike has about 35K miles on her and the cam is original. Cam lobes looked OK and similar to each other just by eyeball. How much variation should I expect?
 
5 thou over 34k? No worries! Those seem like very good numbers to me. I would say that what ever you are using for oil and what ever you are doing for maintenance practices are paying off.

The key word here is Maximum. Who knows what it was from the factory?
 
The head AND barrells are off right now ? Technical data: Material EN 32 5 , Maximum lift inlet .390 in. (9.906 mm.) Maximum lift exhaust: .346 in.(8.788 mm.). Your lower numbers can be construed as cam wear after 35,000 miles but obviously keep checking as pulling the cam is a big job so be sure first. I'm impressed you got that kind of mileage out of a Combat SS radical highlift cam. You must have had a couple of valve jobs during that period of service. A nasty cam with a no nonsense sound ,super high lift.
 
Maybe I should have asked it a different way. At what point do you decide to replace your cam? Seems like a lot of people are replacing cams. Do the lobes just go away on a soft cam as I've seen in some pictures? How much wear is too much?

So I guess my cam is OK. I have always used Kendall 20W50 4-stroke motorcycle oil (the Green stuff). Now the Kendall name has been sold off to someone else but the same green oil is made by Brad Penn in Bradford PA at the same place as the old Kendall Oil. Pennsylvania Crude yeah baby.

I've done 2 valve jobs - a minimal one in early life (a decoke), and one in the early 80's that included new seats put in by Jerry Branch and everything was replaced with new. The cam does seem to pound the rest of the valve train. This time the head is going to Leo Goff as a 40th anniversary treat (Built in Jan '72). The cases have only been apart once for Superblends at 4700 miles when the drive side bearing began growling at me.

Russ
 
I thhink fancy valve springs & shimming to 40 thou of coilbound at full lift help the equation . The rocker shaft shimming / spacers instead of thackery washers cant do any harm .
The Pennzoil that was around a while back , that poured like trecal wasnt to bad . " Pennsilvania Crude Oil , the worlds best crude oil " was the advertisment in the 60s ,
But theyd said it had all run out ? ? The Morey's heavy duty oil stabilizor has simmilar Cling , anti wipe , pressure & heat resistant properties . Stops dry scuffing on start up
and migration under extreme conditions . A true ' Anti Wear ' additive , at ea oil change . Pays for itself in performance consistancy and lower overhaul requirements .

Refaceing / Lapping followers , particularly before installing a new Cam , will save ' a bit ' of bother . Proper cam lube & run in neccesary .
The drag race types used to run in the cam on the bench , or under light load with single valve springs , before installing the secondary ( or primary ) springs .

The W&S sets were substantially more sophisticated than the ' Terrys ' drawn wire type . Thoough they work surpiseingly well , heat will get em eventually .
 
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