Zero Valve Clearance, How best to resolve?

So here's the deal, I rebuilt my 3rd gen motor using a crank case form a 4th gen (as far as I know there is no real difference between 3rd & 4th gen cases). I checked the valve clearances and there is NONE! I assume this is the result of decarbonizing (is that even a word?) the combustion chamber, valves and valve seats. I cant even get my finest (0.025mm) feeler gauge in there.

So how do I figure out what size valve shims are needed? I can see two ways of doing this:

1. Take all the valve shims out, put the cams back in, measure the clearances then subtract the recommended gap and that # will be the size of the required shim.

2. Replace the shims with the smallest ones available (I think 1.20mm are the smallest), put the cams back in, measure the clearances then subtract the recommended gap and that # will be the size of the required shim.

I guess the underlying question is... do you need shims installed in order to get an accurate measurement? My guess would be, yes you do, but I hope I'm wrong because that would mean I would have to buy at least 4 of the smallest shims as well as the ones that would give me the correct clearance. I want to take the cams out as few times as possible because every time I tighten the cam holder bolts it feels like the heads could snap off, or worse strip the threads in the head.

Either way it looks like I'll be looking to buy all new valve shims in various sizes less than 1.75mm in thickness. (All of the shims I have are between 2.00mm & 2.25mm) If anybody has some for sale I'm buyin'.

Thanks for the all the help.

 

Seriously? you guys got nothin'?

 

If you did not surface the valves or cut the seats the clearance should not have changed. Did you change the buckets or shims with the other engine? Just grasping at straws from here but it does not make sense. You do not need to torque the caps just to check the clearance clarence, snug will do as damage to the threads is a real threat.

 

With zero clearance there is a chance that valves could have kissed the piston tops while you turned the engine by hand. Not good.

Something is seriously out of whack on this joint. Are you certain you didn't interchange intake and exhaust cams ??

 

I am absolutely positive that the cams are in their correct locations and that the shims and buckets were put back in their original positions, everything was clearly recorded and labeled during disassembly... AND I watched the pistons through the spark plug holes as the valves opened for the first time to make sure they didn't come in contact. There was A LOT of carbon build up on the valves and valve seats, enough to make me wonder how it could have possibly maintained compression so I resurfaced the valves and seats with light lapping compound just enough to get rid of the carbon. Maybe I was a bit too aggressive, but the compression is good so I'm not worried. I think you answered my question though, you have to have shims installed to get a measurement. I'll score one of those Hot Cams kits and start with the smallest, and do the math. I think Honda uses a special alloy of Aluminum and Butter in its engines. The stuff is creepy soft for a ham fisted guy like me. I had one of the the bolts strip the hole on the way out, pretty sure it was cross threaded by whoever adjusted the valves last.. I re-tapped the hole and used a longer bolt, It's good to hear you had luck with helicoils so I'll track some down, makes me a little less hesitant to do the trial and error. Thanks!

 

Please do not take this the wrong way but it really does sound like there is a problem. Bucket and shim heads are not prone to wear and need little attention. For the clearance to have been lost you would have serious wear to the valve and seat. Lapping would not do that. You did not state the miles on your engine but I do not think it matters unless it is 80k+ and abused. Please use a sharp eye when looking at this as it really is oot of place but I think your OK .....you sound sharper than most mechanics I work with and I am asking Squirrelman's advise on one of my own abortions........never hurts to get a second opinion to put your mind at ease.

 

Thanks for the compliment Toe... I'm not definitely not a good mechanic, I'm just an experienced one... rebuilt my first motor (YZ80) when I was 10... was always taking stuff apart just to see how it worked.

The bike had about 70K HARD miles on it before she blew. The FOOL I bought if from last year knew nothing about taking care of a motorcycle, he put 30K on it in two years and never had any maintenance done, not even an oil change or chain adjustment. He really abused and neglected it, but I got it dirt cheap for the express purpose of tearing it down and making it better than new anyway so I didn't care, I considered myself lucky to find it. Had I checked the clearances before I took it apart my bet is that they would have been pretty snug to begin with and then cleaning it all up made it worse. I have no doubt that the correct shims will do the trick.

 

Finally got the Hotcams kit. Installed 1.5mm+/- shims and found that they were all off by .3mm+/-, which is just enough to give you no clearance at all. At least I now have a measurement of how much carbon can build up on valves with 70,000 miles on them. Kinda makes a case for premium fuel & dumping some fuel system cleaner in the tank every few thousand miles. Again, thanks for the help!

 

So now they're set according to the book ?? I'm a bit confused.

Valve seats sometimes receed with all the pounding and move the vales up toward the cams.

 

Yep, issue resolved. With no clearance you have to put shims in that will give you enough clearance to measure. From there its easy to determine the correct size. It looks like if you just take the shims out you can't get an accurate measurement & it may chew up the nub on the inside of the bucket.