Jamie Posted November 23, 2009 Report Share Posted November 23, 2009 Ok a little history first, Bought an ex-race 2003 (5SL) R6 a year or so ago for my track bike. I figured this year would be a good time to drop the motor and check out what was going on inside the cases as i know it's had quite alot of work done on the tuning front, just a checkup to try and ensure things don't go bang mid session. Everything looks good as can be expected from a low mile jap engine (it's obviously been well looked after despite the fact it's an ex-racebike that's been thrashed). It's had what looks to be a pretty good porting job on the inlet and exhaust and some spangly after market cams with modified duration and lift. these are simply engrave with the part number YAM21. I've managed to track these down as a kent cams product so good stuff if my own previous experience is anything to go by. any way now to my question, the valve clearances are way off. Kent reccomend .2 on both intake and exhaust.... measuring mine the intake ranges from .16(which is nearly the stock clearance) to .26. The exhuast is between .3 and .38. These are miles out am i missing something???? are there any reasons that the guy who did the engine build would have set them .1mm higher than the cam spec (other than incompetance/laziness etc?) Am i wrong in thinking that this must be more than general wear? I'm quite cold from standing in the garage armed with feeler guages so i may not be thinking straight!!!!!! Jamie Link to comment Share on other sites More sharing options...
Mr.Pigdog Posted November 23, 2009 Report Share Posted November 23, 2009 I wouldn't dare to make out i know,but can say that i don't think the clearances would be larger due to wear-maybe he set them large to allow for large amounts of heat??? Link to comment Share on other sites More sharing options...
gsxr renegade Posted November 23, 2009 Report Share Posted November 23, 2009 Could the more agressive profile of the cam caused the shims to wear at a faster rate? I could be talking utter pish, so wait for someone who knows what they're talking about. Link to comment Share on other sites More sharing options...
gsxr renegade Posted November 23, 2009 Report Share Posted November 23, 2009 Shims don't wear - it's the buckets and the cam lobes that wear. Plus the valve seats wear and pinch into the head plus the valve backs themselves wear. And the valve stems stretch.... Ah. I see, I take it that's why you would need thicker shims to maintain correct clearance, as the gap between the cam lobe and bucket increases. Link to comment Share on other sites More sharing options...
Jamie Posted November 24, 2009 Author Report Share Posted November 24, 2009 Thanks for the replys guys! The cams are definitely from kent so as you say mille, they'll be re-ground. the cams look good with no signs of wear on any of the lobes. My last trackday at rockingham the bike was pulling hard with no "signs" that there might be a problem. So my next actions will be to check the valve stems and probably the valve seats. looking down the spark plug ports the pistons have a reasonable coating of carbon on them so i guess this could have built up around the valve seats too. anything else i should be looking out for? I've opened a right can of worms here!!!! thanks again for the responses, jamie Link to comment Share on other sites More sharing options...
Evilchicken0 Posted November 26, 2009 Report Share Posted November 26, 2009 Presume they are re-ground oem cams? Valve clearances don't generally open up unless the valves are bent - I'd check this first of all.. If the valves are straight then it could be that whoever built the engine missed the subtlty that re-ground oems cams will require thicker valve shims because the cam lobe base circle radius is reduced to increase the lift. I'd wager that the amount of exces clearance you've got is the amount by which the base circle has reduced/valve lift increased. I'd tend to go with this senario - how about the last owner got the head ported and rebuilt the enginge then changed the cams after it ... maybe they simply accepted the valves were out but didn't have the shims so decided to do them later. Then they sold the bike. Link to comment Share on other sites More sharing options...
ronenige Posted November 27, 2009 Report Share Posted November 27, 2009 he may have fitted the largest shim's that Yamaha do , its a fairly small range , iirc 1.20 - 2.40 mm , so if you grind a mill off the base circle you could be struggling to get the correct clearance , of the top of my bald bit i think the honda shims are the same size but a much larger range . hth Link to comment Share on other sites More sharing options...
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