Topic: Cam numbers (I should replace, huh?)

[Ravie]

Just got the cam off my 26,000 mile 750 engine which I am rebuilding.

Took measurement of a few lobes and came up with about 295 on intake and 280 on exhaust. That looks to me to be REALLY low. Yes?

I've got another engine of unknown mileage sitting in the shop but I'm hesitant to even check it...I think with these kinds of numbers I might as well poke around WebCams site...

Just looking for confirmation of what I think...

I'm rebuilding this basically to stock, so I don't need anything wild, so if anyone has any suggestions keep that in mind. I'll poke around myself as well.

Thanks

[seanbarney41]

what are you measuring?  I am guessing degrees of duration?  That won't tell you if the cam is worn.  Measure height of lobe vs. base circle and compare to stock specs. (unless it is already an aftermarket grind) You will need a dial indicator.  But really, just inspect the lobes and bearing journals for pitting or wear through of the hardening.  Really, it should be fine after 26k miles as long as it didn't rust or get starved for oil.  Post some good pics and guys can tell you if its useable.

[Ravie]

The numbers I'm posting are the difference between the base circle and the lobe tips.

Intake
1.399-
1.105
_________
.294 lift over base.

Exhaust
1.386-
1.105
________
.280 lift over base

They measure out *under* the minimum the manual says is acceptable which is 1.411 (intake) and 1.392 (exhaust)

There are definite wear patterns but no pitting or anything.

I did it with digital calipers because that's what I have, and I checked them more than once and rocked it to the lowest number to make sure I wasn't off center. Is it perfect? Oh, probably not. I know that...

[seanbarney41]

ok...gotcha.  It would probably run ok and hold up for several thousand more miles but may be better to replace

[Ravie]

That's kinda what I was thinking. I'm not in a huge hurry to finish this bike right now (just trying to get it torn down and inspecting as I go) so I can work on getting a cam, etc.  The 41a looks nice... 

Think I'm gonna have to make a stop at Sears and see if they've got a bore gauge in stock. I got the cylinder head off this morning and gave it a good wash and the cylinders are as shiny as can be(not a hatch mark in sight!), so I'm interested to see how worn they are by the numbers. I have a hunch I'm going to need it bored out.

[HondaMan]

Nope! 
Those numbers (lift numbers) are spot-on for the K3-K6 engines.
Typical nominal intake: .295"
Typical nominal exhaust: .281"

The 1.411" intake overall lobe height is measured across the whole cam, and only applied to the K0-K1 engines. After that, the overall height was typically more like 1.405" intake.

The cams were detuned beginning with the 'new factory' K1 engines, to prolong rocker life, for the most part. It worked, too. It lost about 2 HP total by the K4 engines, but increased compression as the result. This led in turn to the use of 3-piece oil rings, because it was possible for the higher compression to push exhaust gas past the 3rd rings and burn them enough to start letting them fail: the 3-piece rings flex when the pressures rise (instead of eroding) and let some oil slip past during the downstroke, which often appears as blue smoke out the pipes when the 'tamer' cams and 3-piece rings are pushed into the redline RPM ranges.

All this said: the cams like yours are the ones that will last 100,000 miles if you keep up with the oil changes. 

[Ravie]

I feel honored you came to my thread, HondaMan.

Awesome, that's good news.

Here are some phone pics of the wear patterns.




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[HondaMan]

Those marks look very typical. 
I wouldn't hesitate to use it again.

[Don R]

I always like to put a little assembly lube on the bearings, rockers, adjusters and valve tips when putting one back together. New or old just to lube it until the oil gets there.