TOPIC:

zed1015 wrote: Depending on application the Wiseco pistons take into account the use of high lift cams hence the deeper valve pockets to allow adequate clearance.
The clearance you have stated if correct is around 0.5mm wider that the absolute minimum so in theory should be enough.
If the piston crown thickness allows some machining then i'd go 0,5 to 1mm which would give a comfortable amount of clearance but you may not need it.
With the Bathtub head having a slightly smaller combustion chamber volume and therefore slightly a higher comp over the 'J' mean some removal of material from the valve pockets won't result in a significant drop and you will most likely end up somewhere around the 'J's std comp.

I've compensated for the valve angle and larger diameters, with the new set of pistons...and have gone deeper into the piston with the pockets. The dome thickness measures about 1/4" at the thinnest spot (after modification), so these KZ1100 stock pistons do have material to work with, as per Larry C.
I did move the radius ledge toward the piston edge, and left a cove at the base of each pocket rather than a sharp 90 degree inside corner.

LarryC wrote: I can't speak specifically for the stock J piston BUT I can tell you with absolute first hand experience that the OEM KZ900 and 84 GPz11 pistons can be fly cut for adequate valve relieve without issue.

The KZ900 scenario was to use those same GPz cams with stock pistons.
The GPz scenarion was to use Web 109 Grind with stock GPz Pistons.

Clay mock up is only useful to a point. When you want an accurate picture of the relationship between valve to piston clearances at specific instances, the best way is a dial indicator and degree wheel. Set the head up with light springs.

It's possible to accelerate a valve into the piston crown just after ATDC. The cam lobe profile has everything to do with that scenario. Obviously that varies from grind to grind. Every build has to be taken for the components being used and all aspects of modifications have to be considered and accounted for.

Here's the danger in giving someone in your situation a thumbs up that all is well...bolt it together and run it.

You say you had the cams timed correctly. Perhaps you did, perhaps you did not. Was the cam cover installed? Was the chain tension correct? NOBODY on the Internet knows for certain. That's not to slam you...but it is a consideration that can't be ignored. Do you have any idea of how many guys get their hands into these engines and then totally screw up the cam timing?

IF you have everything timed correctly and if you don't do anything like swapping the cam sprockets and if you assemble the top end correctly during final assembly....then the indications are that you have adequate piston to valve clearance.

Do I need to change sprockets on my 84 GPZ camshafts before installing the cams in the 84 ZN (GPZ) head, which is prepared to go on my KZ1100-J engine?
The 84 cams with (Z1100B) sprockets were used for my clearance test with the clay. If I do have to change the sprockets, will it be necessary to do the clearance-test again?

I like your piston fixture. Smart move cutting your valve reliefs... that's cheap insurance IMO. I don't know nearly as much ad Zed or Larry do about these engines, but I have never worried about static measurements with valve clearances its the dynamics of the situation that will do you in.. An engine that's close may run just fine, until one sunny day your out playing around and miss a gear shift....

Better safe than sorry!

zed1015 wrote:

daveo wrote:

zed1015 wrote: Which engine do you want to fit it on.
Be careful with piston to valve head clearances on assembly.
Depending on application you may need to fit different pistons or machine the valve pocket angle to avoid collision etc.

The engine is a 1982 KZ1100-A2 with stock J pistons.

This beauty has shim over buckets with standard J cams.
I was hoping for a simple, straight forward head-swap...now

OE Standard piston I want to use...if possible.

It is the different angle and size of the valves which may cause problems and you need to make sure they do not clip the piston crown.
You need to dry build and cam time the top end with the cams you intend to use.
you can just fit one bare piston, no rings or circlips. then rotate the engine slowly while observing the valve movement through the plug hole and their proximity to the piston crown.
If there is no contact you then need some plasticine placed under the valve head which will get compressed and you take a measurement off that to see how close things are and then you can decide which approach to take.
If using stock pistons you may just bolt the head on with no problems but a higher crowned Wiseco piston etc may need the valve pockets re-angling or fit a piston intended for the model the head came off.

Let's see...it is December now, and normally the annual riding season would be over, but this year there will be several more exhilarating rides to get in before Santa comes.

I still can't believe the amazing performance transformation of this motor!!! It is simply incredible, with only the (member recommended) modification to the (82 Kaw. std.) piston valve pockets...no high compression pistons, or cylinder boring.

Thanks again for the help guy's. I recommend this modification to anyone having a good motor to start with, and hope my posts (and your awesome replies) can assist someone else moving forward with a similar-simple build.

Good for you.
Steve

swest wrote: Good for you.
Steve

Thanks Steve...
For the members that derived benefit, and especially those that provided much-requested advice for my project at the time. A big thanks, and I really hope they get it!