cam lobes

#1
This is an Isky 260/220/104 with many many hours on it. Will someone tell us
what the heck is going on with both lobes losing their integrity? Is it repairable
or has it lived out its life?
 
#3
This is an Isky 260/220/104 with many many hours on it. Will someone tell us
what the heck is going on with both lobes losing their integrity? Is it repairable
or has it lived out its life?
What are you asking? I have a hard time grasping the concept of "many many" hours on a mini bike engine. Is that destroyed metal, or grease? Send them back to Isky if that is metal.

At any rate, measure the base circle, (width) and total height for each lobe. Subtract base circle number from lobe height, and that will give you your lift, and you can determine variation from your 260 and 220 respectively.
 
#5
Hi Dave, destroyed metal. I figured that I had maybe not taken care
of valve lash enough and allowed too much room between lobe and lifter.
It's my only hobby and so ride often and have used this cam 4 years before
going for a new one, try to ride daily.
 
#7
I’ve not seen wear like that with my isky cams but the motors with the most time are still running ok. I had a black mamba in a kart engine that had maybe 10 hours on it when compression release got stuck open and I could no longer pull start it. I replaced that with another and the original lobes look pristine. He does a hard face overlay on them so I’m not sure what happened to yours. What oil do you use? I doubt it is oil related but I am curious. Are lifters messed up as well?
 

delray

Well-Known Member
#10
it's hard to tell by the photo you posted,but you also can sometimes get what I call a marble effect. that comes from multiple layers of rewelding the cam lobe to build it up and then it is reground and harden. then after running it for hours and hours the marble effect starts to show. in your case it almost looks like the metal is coming apart and starting to show some of the welding. also you could of warned into a voided pocket area where the welding was done. this is just a opinion only. just hard to really say without looking at in person and knowing what kind of engine setup it had and the kind of punishment it went through....:scooter:
 

delray

Well-Known Member
#12
No, the lifters are good, Mobil 1 0W20 but one time the motor was idled
without oil after major upgrade. For a good 10 minutes.
like ole4 said, if you ran it without oil. the first thing will go is the cam lobes before the lifters. lifters are made out of a much harder steel then the cam is . it won't take much time for the hard steel to start to chewing up the cam. might be one reason why your lifters still look good.
 
#13
It was a hot humid day and John drank too many beers and didn't remember draining the oil a day
or two before. And that day the new head came in the mail and I was over-joyed to get it put on.
When I realized what I had done, the bottom fell out, I cussed,and cussed, and cussed.
. I'll never forget how bad I felt that day. It's remarkable how long the motor has worked
in spite of the accident, although I tore it down and put in a new piston and rings and rod bearing
for damage control. I'm lucky it didn't gall the cylinder.
 
#14
No, the lifters are good, Mobil 1 0W20 but one time the motor was idled
without oil after major upgrade. For a good 10 minutes.
^^^^^^^^^^^^^^^^^^^^^^

That's your problem. Valve lash would not have affected the nose of the cam because the valve will always be open at that point, regardless of valve lash. The only other thing I'd check for would be coil bind but unless you were running 1.3:1 rockers I don't think that was the issue.
 

65ShelbyClone

Well-Known Member
#15
The pitting is repairable by welding and regrinding the cam again, but at best you only stand to save the cost of a $10 iron cam core. It's not a good idea to weld and regrind an iron cam more than once anyway.

Ignoring the history of running without oil, lobe pitting is something that can just develop from lots of run time. It tends to happen where the most force is concentrated on the smallest area like the nose of the lobe.

No, the lifters are good,
They might look OK, but they shouldn't be reused at this point.
 
#16
Good morning, sir. Happy New Year.
What a super forum OMB is for all-things-mini and all-things-small engine...
I learn something everyday it seems.

65SC, I just remembered, this cam was installed years ago when I dropped a valve in a
Chinese head, and prior to that, I bent and broke a pushrod until I got short
enough for this head. This was before running without the oil. Would these things
factor in someway?
 

65ShelbyClone

Well-Known Member
#18
65SC, I just remembered, this cam was installed years ago when I dropped a valve in a
Chinese head, and prior to that, I bent and broke a pushrod until I got short
enough for this head. This was before running without the oil. Would these things
factor in someway?
It's possible, but hard to say.
 

delray

Well-Known Member
#20
you know it's not impossible to make a tool to grind cam lobes(youtube it). if you have the ability to run a cnc mill or lathe and have computer program skills, a guy could fab up is own grinding machine. thing is, the time your done making one your better off spending $100+ and have someone else that does it for a living. it's just not knowing how to make a grinding machine. it also is knowing how a cam works too.
 

Top