Cam Bearings

On my J motor build i am noticing a slight tight spot on the intake cam in one small spot on rotation. Very slight drag, should it be addressed? The bearings are original to the 81 engine. My head machinist inspected them while installing the oversized valves and thought they looked good.

Measure the tolerance with plastigauge, if within tolerance all good. 
If tight the you can shim the cam cap using a shim cut from a soft drink can which is 100 micron thick. If you just shim one side then the cap will lift 50 micron if you do both then the cap will lift 100 microns. 
Retest with plastigauge to check the tolerance after each. 
If you leave it tight you risk oil starvation to that bearing. 

It's a simple solution to an otherwise difficult to resolve problem.

If it's no7 bearing I had exactly the same issue on my J motor.
Ive run shims on many engines to rectify your exact issue. 

If this is a dry build on the head without valves in, try another cam. I had this on a known good head with original cam caps, Put another cam in, issue resolved. The cam must be slightly bent if it's only tight on part of the rotation

Sage advice Moizeau!! Was going to mention that but doing other crap. If like Moiz mentioned, rotating the "dry" camshaft in it's place and note a tight spot, see if it does the same 180degrees out. So Two tight spots. Have to know these heads can also warp creating the same episode. Sometimes merely bolting them down will straighten out what you are experiencing. If you have to shim the caps then something is a miss. Let it be known these J heads are relatively cheap and abundant if the need arises. There are two versions that i know of, maybe more? Don't work on a lot of the newer J engines.   

Also with the "J" the inlet and exhaust cams are interchangeable so before sourcing another cam you could swop what you have to eliminate the cam as the source of the problem

Well, we swapped the exhaust cam to the intake side, and it rotates freely as it should, so it seems to be a cam journal problem. After measuring the journals on the intake there is a one-thousand-inch difference which would cause a tight spot, i think. I emailed the supplier so am waiting for a response.

Formula264 wrote:

After measuring the journals on the intake there is a one-thousand-inch difference which would cause a tight spot, i think. I emailed the supplier so am waiting for a response.

Pattern bearing shells are false economy and are known to have clearance issues so it's best to only use Genuine Kawasaki items which are still readily available although at a higher cost but you do get what you pay for.

 

zed1015 wrote:

Formula264 wrote:

After measuring the journals on the intake there is a one-thousand-inch difference which would cause a tight spot, i think. I emailed the supplier so am waiting for a response.

Pattern bearing shells are false economy and are known to have clearance issues so it's best to only use Genuine Kawasaki items which are still readily available although at a higher cost but you do get what you pay for.


 

Couldn't agree more Rob, however in this case he is using aftermarket performance cams and it sounds like the journals on the inlet are ground slightly "oversize"

zed1015 wrote:

Formula264 wrote:

After measuring the journals on the intake there is a one-thousand-inch difference which would cause a tight spot, i think. I emailed the supplier so am waiting for a response.

Pattern bearing shells are false economy and are known to have clearance issues so it's best to only use Genuine Kawasaki items which are still readily available although at a higher cost but you do get what you pay for.
 As of now they are the original bearings, mind you I don't know if they have ever been changed.

 

These are the measurements of intake/exhaust....see any problems?

The actual measurements of the cams is less important than the "clearance" between the cam and bearings measured with plastigauge. What is interesting is when you swopped the cams the "thicker" cam turned without issue. This would suggest cam to bearing interference isn't the issue (check with plastigauge) worth checking the area of the cam that controls end float as a possible cause and also as Clay mentioned you could bolt the head down with the old head gasket (to remove any twist in the head) and see if the issue is still apparent

I was advised not to use the cams from the manufacturer from where they were sourced due to poor quality so I sent them back for a refund. I ordered new cam bearings [Japan] and my plan now is to use the stock J motor cams dialed in at .110 lobe centers to start, and obviously I will be running race or AV gas. I'm okay with the race gas situation since this is just a play bike and won't be ridden that much.