APE Heavy Duty Engine Studs.

POWERSTROKE_FAN gave me a heads up on the oil hole clearance in cylinder when using Heavy Duty Studs.

Did u drill out ur oil passages in your jug? I didn't before but since I have it apart I got to measuring the dia of the studs and the dia of the whole as zed1015 talked about before, and the casting really do taper a lot to the center. I drilled mine out this time around. There wasn't much room for the oil before so it really had to be restricting a lot of oil to the head. I just took the biggest drill bit that would slide thru there and measured from that. But I cant remember the exact measurements, but I had to drop at least two bit sizes to go thru from the mating surface compared to the center.

If you examine the two stud types, you will clearly see the problem. The stock is tapered as the APE is one diameter though out.

The member said that the diameter of the stud and oil passage of the cylinder can be extremely tight on some castings. ZED 1015 confirmed the post.

kzrider.com/forum/2-engine/590842-engine-case-studs#605011

I had just installed the APE studs and was very concerned with the clearance. It was evident that the clearance was to tight and would chocked off the oil getting to the top end.

I ended up having to drilling out this passage to correct the issue and provide the proper clearance to the top end.

If you change cylinder studs, just check this.......I have seen threads on here where others have just run them without drilling and had no problem.

So you did see how tight it really gets in the center? I ran studs for a few years with no damage, But I did notice that while turning the motor over by hand with the valve cover off, that it just didn't pump oil to the top end as well as stock studded bike does.

Thanks for heads up.

Probably a bit late now but have you thought of "dry blocking"? Some of the bigger cc
bikes on here have it. And it would look real cool on your ride. Next time I pull my head off
I will definately look at this.

This ranks right up there with the coil real mod :S

Did you burn down a cam? If NOT....you have no problem to solve.

I looked into this issue and here again is the facts getting in the way of a good story.

I ran my bike with factory studs until warm. 3-psi oil pressure.
I ran my bike with APE Studs until warm. 7-psi oil pressure.



The oil pressure is taken before oil enters stud passage.

The increase in psi is a clear sign of restriction in the oiling system.

Stock Stud Diameter: 8.0 mm - measured in the middle of stud.
APE Stud Diameter: 9.50 mm - measured in the middle of stud.

Stud oil passage Hole ( Cylinder Block ) narrowest point: 10.40 mm
This was found in middle of block, were castings line or convergence was found

Stud oil passage hole ( Cylinder Block ) widest point: 10.80 mm

Measured several time with digital gauge.

Years ago when fitting a stock block over HD studs the block wouldn't go down further than around half way due to the narrowed casting ( The head of a stock stud would scrape through but the full length of the hd stud would jam ).
This is what alerted me to a potential issue and I always check the casting and clearance any if needed especially the rear two oil feeds.
Not all the blocks are as bad and in fact I haven't seen one as bad as that first one since so maybe it was an extreme case,( Monday morning/Friday afternoon job )
Never gone as far as comparing the the oil pressure though, it just seemed the obvious thing to do "just in case" from a hands on mechanical point of view.
Nice to see some evidence that I wasn't wasting my time though.

I think its a great thing to point out, Im glad you mentioned it in your earlier posts. I was running hd with stock block. I noticed my top end seems a little quieter now. Its cool 4thekz1000 got those measurements to show that it is really restrictive.

That's interesting. It still doesn't prove anything. How does that prove that you have choked the cam journal oil hole?

You guys just like to fuck with your bikes. There have been thousands of sets of those studs installed without issues. If there was a possibility of starvation...APE would tell you to enlarge the stud hole. Do you think for one second they're stupid?

I've got some of each stud, HD & stock as well as some blocks sitting around. As soon as I get some spare time I'll CC a stud hole with each stud size in it & then find and run the formulas. What's a crying shame is that Jay doesn't come here anymore because of the situation that I won't delve into...call it politics for lack of a better word....

Larry is correct on this, you guys are WAY overthinking this. I have ran APE studs on numerous engines, KZ650, GPz1100, KZ1000 and the KZ900 engines along with Honda, Suzuki and Yamaha engines and NEVER had an issue with them. You are trying to come up with a solution for a non problem.

Look at the size of the cam journal hole and the passage leading to it from the stud hole.

If you were starving the cam for lube you would have a burned down lobe. Don't fix what isn't broke. Spend the time micro aligning your drive chain instead.....that's free HP

As far as I am concerned we do not have to reinvent the wheel. I have done more than a 100 + W/O issue.