Cam/valve clearance

Hello , I just joined this site although I've read a lot as a guest.
I a76 kz900 . 1075 12:1 MTV pistons. 37.5mm intake, 31mm exhaust valves. Head has been milled. I have Andrew's 3x cams and my engine builder isn't able to get the Cam, valve clearance right. He seems to think the cams are too big. I had this same engine set up back in 92 with no issues. The only difference the engine in 92 didn't have oversize exhaust valves.
Any and all info would be greatly appreciated. Thanks Randy

Welcome to KZRider
Sounds like your builder didnt grind the valve stems to achieve the proper clearances
Do you have a factory Manual
Dave

A set of GPZ 1100 UT related grid cams had a larger base circle as the Z1 cams that need some mods of the valve train.

Yep when installing OS valves you sink them to get proper valve to valve clearance requiring either valve stems nipped down or smaller base circle cam.

zed1015 wrote: It sound's like whoever did your head did not set the valve stem heights and you should take the head back to them rectify.
If this was your engine builder I would find another mechanic.
The 3X cams would be stock or reduced base circle cams.
The stem heights should be minimum 37.2mm to 37.7mm to allow a reasonable choice of shim sizes .
Max height is 38.2 and you are out of clearance.
This can be achieved by tipping the valves or by the use of 'J' valves which have a 1mm shorter stem depending on the current clearances.
The 31mm exhaust should not have needed sinking but the 37.5 would to achieve correct valve to valve clearance.

Hello I bought the head off eBay. The valves had been cut but was too short to get proper valve clearance. I took the head to have the valves repeated and new stainless steel valves installed. The valves are shimmed with proper clearances now but my engine builder seems to think the cams are hitting the valves at some point when rotating the engine. Any suggestions , ideas. ? Thanks

Hello, thanks for the input. The problem isn't getting the valves shimmed. They are shimmed with the correct clearances. My engine builder seems to think the cams are contacting the valves when rotating the engine. Any ideas, suggestions. ? My engine builder has been building z1 engines for 40 years.

Funtimes wrote: Hello, thanks for the input. The problem isn't getting the valves shimmed. They are shimmed with the correct clearances. My engine builder seems to think the cams are contacting the valves when rotating the engine. Any ideas, suggestions. ? My engine builder has been building z1 engines for 40 years.

So the problem is the valves are being lifted when the cams are rotated ?
And you have the proper clearance when the cams are on the base circle ?
And your builder has been buildiing Z1 engines for 40 years ?
Correct ????

Hello, yes I believe so. Not sure if the valves are being lifted but there is Cam to valve interference somewhere. The 3x cams have 418 lift, 282 duration, both intake and exhaust. My engine builder has built many engines over the years but seems to think something strange is up with my head. He has a 76 kz900 with same set up as mine except he installed Cam motion z4 cams in his...420 lift , 270 duration.

If you have correct clearance then the following problems could be present if the head was not properly prepped for the high lift cams.
1. Bucket bores not clearanced for high lift cams and the cam lobe is hitting the head casting and also the underside of the cam cover. The raised cast crosses need to be removed from the cover..
2. Not enough valve to valve clearance and the valves heads are clipping each other on overlap.
3. Valve guides are not short enough for the cam lift so the retainers are hitting the top of the guides or stem seals. APE guides needed.
4. Piston valve pockets are not deep or wide enough for either the cam lift or increased valve size and the valves are contacting the piston crown.
5. Valve springs becoming coil bound.
6. Valve timing incorrect.
7. All this is basic stuff and it sounds like your builder isn't as experienced as he leads you to believe.
8. There is no such thing as "something strange going on" unless the mechanic doesn't really know what he's doing.

Thanks for the input. I will run all this by my engine builder. I have complete confidence in him. He came highly recommended. He has 4 of the old z1 S that he has built. One with a turbo kit. He also has a couple of the newer laws...zx14 is one.. He did mention in all his years of building engines this is first time he has seen the oversized exhaust valves. Not sure if that is the problem. ?

Am assuming that the cams were degreed in. That is essential for any kind of head mod's. ?