I noticed a light ticking noise......Originally posted by 86atc250r@Jul 1 2004, 11:36 AM
Did you notice any abnormal valve noise after rebuilding the engine?
Would have been a ticking like valves were slightly out of adjustment.
My guess is that you didn't have enough piston to valve clearance with that setup - it's a good idea to clay the piston to valve clearance when swapping parts like this.
With the valves lightly rubbing the piston, it would have likely lasted a little while - and probably broke at a high RPM point - possibly when the valves floated or maybe just when that one valve had enough stress that it finally gave up.
CRF cam -- I haven't measured the cams myself, but I've been told by a top engine builder to not use the CRF cams - the TRX engine needs more low lift duration than the CRF cams provide because of the differences in flow characteristics of the head (TRX has smaller ports). I was also told that the CRF cams are pretty different than the HRC - may not appear that way if you look at basic lift and duration specs, but are very different when you look at the actual lobe profile. He also went on to say that it's very likely you would actually lose power with a CRF cam.
180 degrees out --- It is not possible to set the cam in a 400ex or a 450R 180 degrees out. In fact, it is not even possible to determine what would be 180 out on one of these engines. 90 degrees out is a possibility & would cause immediate and serious problems.
Trying to keep from replacing the head --- price a new cylinder head before putting any time and parts into your old one, with the price of a TRX cylinder head being as low as it is, you machine bill will quickly become greater than the price of a new head.
mixxer,Originally posted by mixxer@Jul 5 2004, 09:23 PM
Why does 86atc250r know so much? The differences in cam compatibility comes from the longer stroke on the trx motor. The dwell, or how long a piston lingers near top dead center, is a function of crank pin offset(stroke) and the length of the rod. when you change either it changes the geometry that changes dwell near TDC.A little bit of modeling clay can save a LOT of money! Next time you assemble with a different cam put a little clay lump in the pistons valve pockets, oil the valve faces , and assemble enough to turn the engine over by hand (don't kick it) . After rotating, disassemble and check the clay thickness in the valve pockets - anything less than .060" can cause you a very sharp pain in your wallet! All that being said, my SWAG puts your timing at 1 tooth advanced pre-catastrophe.