Panhead lost compression
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Panhead lost compression
Good Morning,
Mystified and stumped.
65 Panhead with STD heads. I went through the top end 2 winters ago - new rings, valves and pistons. Bike running great all last year and the beginning of this riding season. Then - some loss of power in 4th and then 3rd gear on the freeway - limped it home. Next day ran fine. Repeated this cycle a couple of times. Finally took a dump a few weeks ago and stranded me. Horrible backfiring through exhaust and loss of power.
Got it into my shop and checked timing - spot on. But compression is 12 lbs in the front and 0 lbs in the rear. Pulled the rear head - pics below. The intake valve and seat are pristine, but the exhaust valve seemed like it wasnt quite closed and a lot of carbon. I forgot to do the "add a teaspoon of oil" thing on the compression test - but will do that on the front cylinder before I pull the front head.
Looks like to me the exhaust valve has carbon on the valve seat - would this keep it from closing all the way? Easy enough to replace the valve but what do I do to the valve seat?
Mystified and stumped.
65 Panhead with STD heads. I went through the top end 2 winters ago - new rings, valves and pistons. Bike running great all last year and the beginning of this riding season. Then - some loss of power in 4th and then 3rd gear on the freeway - limped it home. Next day ran fine. Repeated this cycle a couple of times. Finally took a dump a few weeks ago and stranded me. Horrible backfiring through exhaust and loss of power.
Got it into my shop and checked timing - spot on. But compression is 12 lbs in the front and 0 lbs in the rear. Pulled the rear head - pics below. The intake valve and seat are pristine, but the exhaust valve seemed like it wasnt quite closed and a lot of carbon. I forgot to do the "add a teaspoon of oil" thing on the compression test - but will do that on the front cylinder before I pull the front head.
Looks like to me the exhaust valve has carbon on the valve seat - would this keep it from closing all the way? Easy enough to replace the valve but what do I do to the valve seat?
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Re: Panhead lost compression
It looks like your exhaust valve was not closing completely, which could lead to the deposits on the seat and the valve seating area.
You can clean them off, and as long as the surfaces don't have any damage, you should be able to run them again.
Just make sure that the valves are closing completely when the engine is cold.
Do you have hydraulic or solid lifters?
You can clean them off, and as long as the surfaces don't have any damage, you should be able to run them again.
Just make sure that the valves are closing completely when the engine is cold.
Do you have hydraulic or solid lifters?
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Re: Panhead lost compression
Solid lifters. Awesome thanks for the response. I will clean it up and put it back together and test.
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Re: Panhead lost compression
When you finish the assembly, turn the heads over and fill them with a thin oily liquid.
Gasoline comes to mind, but can be very dangerous to use.
Whether the head and valves hold the liquid will be your proof.
Gasoline comes to mind, but can be very dangerous to use.
Whether the head and valves hold the liquid will be your proof.
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Re: Panhead lost compression
I think you need to figure why this happened, just cleaning it up will produce the same results.
Re: Panhead lost compression
I havent seen where you checked pushrod adjustment. I wouldve cheked that first and foremeost before removing the head. Check and adjust with the motor stone cold
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Re: Panhead lost compression
Also note that after you first assemble and run the engine, and retorque the head bolts, you should check the pushrod adjustment again.
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Re: Panhead lost compression
Agreed, checking adjustment before disassembly should give a clue. There’s a lot of oil, I guess, in your combustion chamber. When you did the compression test, was there compression but it was blowing out the exhaust? Or was there little to no resistance like blowing by the rings? Maybe just assemble the head with valves, no pushrods and see the resistance/suction at the spark plug hole. Zero compression is serious and not just a leaky valve, and if a valve did tighten up, why would the other cylinder also mimic the same symptoms?
Just a guess but the last time I saw this happen, (compression going away in an otherwise good motor) it was gasoline that a jilted girlfriend has dumped a big load of sugar into. Got recent enemies?
Andygears
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Re: Panhead lost compression
My Mikuni carb needs replaced. I have parts for an SU carb and may put it on at reassembly.
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Re: Panhead lost compression
If the valves were improperly adjusted (not closing all the way) and run for a while, then the buildup you are seeing on the seats could have have been holding the valves open and making it seem like the pushrods were adjusted properly when you checked them before disassembly.
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Re: Panhead lost compression
jus a thought ....make sure you adjust valves to solid spects ....dont adjust according to hydraulic spects