Shim Under or Shim Over?

At what point on a KZ1000 (specifically 1977) does one have to make the move to shim-under tappets?

Is it strictly a lift thing, or does it have more to do with how the cam opens the valve?

I have heard of shims getting spit out even with stock cams, and I have heard that somewhere around .400" is the limit, regardless of the cam profile.

Do heavier springs make a difference?

-Dave

id say.400 is pretty safe cut off point,also depends how its ridden.if TB is behind the bars sidestepping clutch at 12,000 rpms i dont care what kind of bucket it is,im plugging my ears! :laugh:

I am running .420 cams on my GPz1150 and am using SOT buckets. I have reved it to about 10000 with no problems. The problems start to manifest when you decrease the base circle on the cams to increase the lift.

I don't think you can go much over .400 anyway without grinding the head for clearance. Better safe than sorry.

How exactly is the head ground for clearance?

I already took out the cross marks in the valve cover by hand with a die grinder. They cleaned up pretty nice, but this seems a bit crude for grinding on the head itself, especially around the lifter bores.

Milling machine? lathe?

-Dave

How modified and ported is your head? If it is stock than don't even bother going bigger than about .365 lift (WEB #318 grind)it would be a waste of time and effort. To go larger than that on a stock motor is like sending an Alzheimer patient to the University. If you plan on doing a good porting job on the head and putting in larger valves, than just send it to Larry C. and he will take care of everything. This should explain everything.
www.flowbenchtech.com/porting/CRH/kz-data.htm

Just out of curiosity and for upgrading my brain here....

Under bucket shim configuration/conversions...
How the hell are the shims replaced?

Meaning you have to remove the camshafts (lift up) to change the shims for clearance specs.... :ohmy:

That seems like a total PITA... I can also see where due to constant removals, striping a top idler bolt/thread or cam cap bolt/thread would be come highly possible...

No thanks, .365 cams with over bucket shims is good enough for me.... I have enough issues to deal with... :blush: :laugh:

I agree with you OMR. I wouldn't put the shims under the bucket for any amount of money.

I can see see me now adding the figures to get the correct shim,ought+oughtequals? :laugh:

When i replaced my head gasket on the 1075 engine everyone was telling me i coul not run a 418 cam. Had me freaked out so i starting reading.

On the Ape site it said no bigger than 418 so i still run 418.

theres a certain year i wanna say 82-83 j-series shim over buckets that do a better job of holding in shims versus older style,ive got some in a box someplace ill have to dig up to see if anybody recognizes them.

PLUMMEN wrote:

theres a certain year i wanna say 82-83 j-series shim over buckets that do a better job of holding in shims versus older style,ive got some in a box someplace ill have to dig up to see if anybody recognizes them.

When you find them take some comparison pictures. I would like to see the differences. I thought they were all the same. As I mentioned before, I am running .420 on a 84 GPz1100 head mounted on a J motor. The head is very well ported and the engine pulls like a monster. All this with SOT buckets. I even took the time to machine down some Titanium SUB retainers so I could use them with the SOT Buckets. 10K RPM and no problems.

The head is already ported and I have new valves. guides. springs,etc... so it should be able to take the big cams. If I don't like how the cams perform, i'll just take them out and put my andrews 2x cams back in.

<RANT>it seems like every time I ask a question about building up my head, I am told to just have Larry Cavanaugh do it, "I'm going to screw it up", "don't bother, its a PITA", and so on. It's not that I don't have enough money to send my stuff out to get done, but simply that I want to learn and to do it myself. I have already ruined a junk head I got on eBay by experimenting. I'm bidding on another right now. I got some EXCELLENT, and very specific advice from Larry on how to port these things, and it is coming along nicely. I love screwing around with motorcycles - it's about the journey, not the destination. If my bike was perfect and never broke and was as fast as a Hayabusa, then what fun would it be? I wouldn't get to take it apart and put it back together again a million times.
</RANT>

But.. back to our regularly scheduled program:

I can't find any info about how you clearance the head for the cams - on Larry's site or anywhere else. Any ideas?

-Dave

i know you don't want to hear it but i would take it to a machine shop to be cleared for the cams.
you need to clear the lifter bucket area and a little on the sealing edge.
i have a j head i bought off e-bay and someone did it with a die grinder. they did a poor job.
you can port it yourself but there is more to it then just hogging it out.

it's hard to see but enlarge the picture and look at the lifter bores and the outside edges where the cam tip would contact.