Hot Cams - No Tappet Shim Clearance

[mrbridgeport]

I just don't get it.

I installed new MegaCycle cams in this fresh engine build and for the life of me I can't figure out this clearance issue (or lack of) I am getting with the shim tappets. First some history: 77-GS750 bored to 851, installed Henry Abe pistons, rings etc. Now to the head. I had it ported and polished and sent my cams out to Mega Cycle. Their 381-70 kit specs:
.380" 261? 107.5? All around road, road race performance. 23 btc/58 abc .006".380" 261? 108.5? Top-end power. I used a Kibblewhite spring kit and Titanium Kibbelwhite Retainers and new keepers.

I installed the original valves ( which where in tolerance), lapped the valve seats and installed all the bits and cams.

Now that I have it all installed everything (and a couple knowledgeable friends have checked my work) I can not get correct tappet clearance. Even 2.15mm tappet shims are too large.

Megacycle specs say that this kit can use the original buckets and shims (Shim Over). I don't get it.....Has anyone been through this...what am I missing????

[Nessism]

Were the valve seats and valves cut? If so, you need to have the stem cut to shorten the valve.

[mrbridgeport]

Hi Nessism,

I did not have the valve seats or the valve stems cut, I only lapped the valves.
I used the same valves which were in tolerance. Do you think I'm going to have to cut the stems so I can get some clearance. I'm at a loss..thanks for the help.

-joe

[Nessism]

If you didn't cut the valves or seats, then my guess is the cam base circle is larger than stock. I believe your only choice is to shorten the valves. It's a simple process but you will have to remove the valves to do it.

[mrbridgeport]

Thanks Nesism,

Sounds good, makes sense. Guess I know what I'm doing tonight. I'll report back with results.

-joe

[rapidray]

Measure the cam's base circles. while it is rare for a cam manufacturer to INCREASE the base circle, anything is possible. If you find the base circle is larger, you will need to shorten the stems HALF of the increase in base circle measurement. Ray.

[mrbridgeport]

Thanks Ray, will do tonight if I can stand the heat in the shop.
I will also call Mega Cycle and see if they do infact increase the base circle. Thanks

[mrbridgeport]

Hi Guys - I just got off the phone with Jim at Megacycles. To answer rays question. MegaCycle does not add to the base circle diameter but actually decrease it by about .010. He seems to think it may be that the Kibblewhite Titanium Retainers may not be sitting in the shim bucket completely (there is a small radius on theinside wall of the bucket) or the keepers may be square cut instead of round cut profile (or viseversa) and lastly I need to measure the installed height (w.o the springs in it using tubing cut to about an inch in length and measuring the overall height using a dial indicator)...

[gearhead13]

Arent titanium retainers made for shim under bucket? Check that the valve and not the retainer is making contact with the bucket.

[Nessism]

If you pull the cams and then one of the buckets, you might be able to see if any portion of the retainer sticks up above that of the valve stem. The bucket has a little nub in the inside that pushes the valve stem so any raised area on the retainer would have to be taller than the nub.

[mrbridgeport]

Headed out to the hot garage now, time for inspection. Will report back

[mrbridgeport]

Well, after further inspection, it is in fact the titanium retainers. They are not letting the valve stem touch the bucket. It looks like I will either need to run Shim Under Buckets (which I don't know where to get as of yet) or pull the head and run the original retainers. Any ideas?

[mrbridgeport]

Looks like Kibblewhite may have a misprint / partnumber in their catalog...hummm

[Guest]

Kibblewhite does not catalog a shim on top style Ti retainer for the 2 valve 750 or 1000. If you ordered part number 60-6106, it clearly states SOB retainers.That stands for "shim on bottom".

You could probably use them if you machine the shim holders off.

[mrbridgeport]

You are totally right. It was actually Megacycle that had the misprint and sent me the ti retainers. There PDF Catalog states the ti retainers can be used shim over but they were wrong. They are sending me some shim under buckets now. I should get them Tuesday. Now I need to take some measurements and find me some shims that'll work. What a pain