Cam Gear Slippage
01-06-2008, 06:19 PM
#1
Drifting
Thread Starter
Cam Gear Slippage
My silber 78 recently started missing and backfiring out of the exhaust AND intake. Just pulled the passenger side cam gear cover and discovered the belt was in bad shape (frayed front edge and partially missing teeth) but still on the mark at TDC. The belt is long overdue for replacement but the sparkplugs, wires, filter, distributor cap/rotor and vacuum lines are all in good shape.
Is it possible that the drivers side gear has slipped but not the passenger side? Broken cam? I can't tear it all down right now since the garage is currently being used for storage (another story
).
Dennis
Is it possible that the drivers side gear has slipped but not the passenger side? Broken cam? I can't tear it all down right now since the garage is currently being used for storage (another story
). Dennis
01-06-2008, 06:31 PM
#2
Team Owner
disconnect your battery, so someone doesnt start the engine, till you replace the belt, and find the cause of the fraying, might have a bad tensioner roller or water pump shaft may be bending in the housing
01-06-2008, 07:04 PM
#5
Drifting
Thread Starter
Marton, I haven't checked the rubber between the throttle body and the upper chamber, but the rest of the vacuum lines are OK. Also, a large vacuum leak would cause the backfire in the intake (lean burn) but not through the exhaust (rich burn). That is what has me confused and (heaven forbid) made me think of a broken cam shaft.
Dennis
Dennis
01-06-2008, 07:22 PM
#6
Drifting
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Well a vacuum leak in my 82s upset the mixture control somehow; so called "false air syndrome". I had a leak in the rubber between the throttle body and the upper chamber due to the clumsy way I put the upper chamber back & so kinked the rubber. That gave me some exhaust back fires but mostly a big flat spot around 1500rpm.
On mine there are some vacuum lines under the upper chamber which are also hard to check.
Marton
On mine there are some vacuum lines under the upper chamber which are also hard to check.
Marton
01-06-2008, 07:42 PM
#7
Drifting
Thread Starter
Marton,
I haven't had my upper chamber off on this 928 but it could have given up the ghost after 30 years. BTW this is it 30th birthday sometime this month. After the backfiring it probably has at least a few vacuum leaks now.
Mrmerlin,
The engine is non interference as I was able to turn it over with no hard spots and no grinding noise.
Thanks all,
Dennis
I haven't had my upper chamber off on this 928 but it could have given up the ghost after 30 years. BTW this is it 30th birthday sometime this month. After the backfiring it probably has at least a few vacuum leaks now.
Mrmerlin,
The engine is non interference as I was able to turn it over with no hard spots and no grinding noise.
Thanks all,
Dennis
