How to reset cams to TDC? (More info now)
08-08-2008, 08:40 PM
#1
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How to reset cams to TDC? (More info now)
My AHA engine blew- looks like one of the tb idlers fell apart. How do I set the cams to TDC? I can't turn them more than a few degrees, and they bounce back.... I appreciate any help.
edit: I'm using the bolt at the center of the gear with a 1/2" breaker bar. I know it's going to put the bolt excessively tight, but I'll use the lockbar when I remove the bolt anyway. Any suggestions about how to turn the cams? I'm thinking there must be enough internal damage in both heads to justify pulling both heads and scrapping any attempt to do a leakdown test.
Thanks!
edit: I'm using the bolt at the center of the gear with a 1/2" breaker bar. I know it's going to put the bolt excessively tight, but I'll use the lockbar when I remove the bolt anyway. Any suggestions about how to turn the cams? I'm thinking there must be enough internal damage in both heads to justify pulling both heads and scrapping any attempt to do a leakdown test.
Thanks!
08-09-2008, 04:59 AM
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how hard are you pushing on the bar? Remember, you need to overcome the spring pressure. On the
hand, it is possible you've got bent valves (at a minimum) and no amount of pressure will budge them.
08-09-2008, 08:03 AM
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How much pressure?
I was cranking on that bar, and could not get the cams to move. Should I use a prybar in the spokes of the gear? I had assumed that there was a good deal of internal damage because I never had to put anywhere near that amount of force on that breaker bar to rotate the engine (cams with the crank), let alone just one cam. Are you saying that I need to just force the cams into place once the crank is at TDC? I'm trying to avoid further damage. The cams were off about 150 deg. from each other, and they were at least 90 deg. out of line with the crankshaft... So just force them into place?
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08-09-2008, 09:30 AM
#8
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No Half credit! Most of the cam torque is valve train friction...
Cam torque from valve springs is close to net zero, some spring force being exerted on on the leading and some on the trailing cam surfaces.
08-09-2008, 09:36 AM
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Don't force it! You most probably are trying to force either a good or bent valve into a piston...
Looks to me like your next step is head removal.
08-09-2008, 11:17 AM
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sorry prof, I'll disagee with you here (maybe earn EXTRA credit??). What you are implying is
that without spring pressure, the cam shaft STILL would be fairly difficult to rotate - which could only be from the valve stem seals, and the very nominal pressure the valve stems would be exerting on the cam lobes. I've never tried it that way, but I bet it would rotate fairly easily, and that well over half the pressure/resistance is due to the springs. The valves themselves should slide easily in the seals, and they should also follow the cam lobes easily with no springs.
Just my $.02 (no fat wallet here!) and trying to earn my credits back.
What say you?
Just my $.02 (no fat wallet here!) and trying to earn my credits back.
What say you?