Panhead lost compression

All Panhead related discussions, questions etc.
Post Reply
Edaddy
Member
Posts: 102
Joined: Tue Dec 05, 2017 8:49 am
Bikes: 1965 Panhead
1992 Jammer frame
43" Custom Springer
1991 Std Case
STD dual-plugged heads
Location: Bellingham wa
Has thanked: 9 times
Been thanked: 21 times

Panhead lost compression

#1

Post by Edaddy »

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?

IMG_1146.JPG
IMG_1146.JPG (629.73 KiB) Viewed 637 times
IMG_1154.JPG
IMG_1154.JPG (628.61 KiB) Viewed 637 times
IMG_1153.JPG
IMG_1153.JPG (636.23 KiB) Viewed 637 times
IMG_1152.JPG
IMG_1152.JPG (628.22 KiB) Viewed 637 times
IMG_1148.JPG
IMG_1148.JPG (691.36 KiB) Viewed 637 times
IMG_1147.JPG
IMG_1147.JPG (556.69 KiB) Viewed 637 times
awander
Senior Member
Posts: 2082
Joined: Fri Sep 21, 2007 3:03 am
Bikes: '52 FL
'64 FLH
Has thanked: 163 times
Been thanked: 511 times

Re: Panhead lost compression

#2

Post by awander »

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?
Edaddy
Member
Posts: 102
Joined: Tue Dec 05, 2017 8:49 am
Bikes: 1965 Panhead
1992 Jammer frame
43" Custom Springer
1991 Std Case
STD dual-plugged heads
Location: Bellingham wa
Has thanked: 9 times
Been thanked: 21 times

Re: Panhead lost compression

#3

Post by Edaddy »

Solid lifters. Awesome thanks for the response. I will clean it up and put it back together and test.
andyinlz
Member
Posts: 60
Joined: Fri Jan 13, 2012 11:42 pm
Bikes: 1967 FLH
1959 FLH
Other H-Ds
Been thanked: 4 times

Re: Panhead lost compression

#4

Post by andyinlz »

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.
pan620
Member
Posts: 219
Joined: Fri Dec 30, 2005 2:28 am
Bikes: 62 Duoglide, 48 Pan, 1990 FLHTCU
Location: Kansas
Has thanked: 299 times
Been thanked: 63 times

Re: Panhead lost compression

#5

Post by pan620 »

Edaddy wrote: Sat Jun 12, 2021 3:52 pm Solid lifters. Awesome thanks for the response. I will clean it up and put it back together and test.
I think you need to figure why this happened, just cleaning it up will produce the same results.
melvinjo
Member
Posts: 38
Joined: Tue Sep 22, 2020 3:21 pm
Bikes: 60 FLH
Been thanked: 12 times

Re: Panhead lost compression

#6

Post by melvinjo »

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
awander
Senior Member
Posts: 2082
Joined: Fri Sep 21, 2007 3:03 am
Bikes: '52 FL
'64 FLH
Has thanked: 163 times
Been thanked: 511 times

Re: Panhead lost compression

#7

Post by awander »

Also note that after you first assemble and run the engine, and retorque the head bolts, you should check the pushrod adjustment again.
Andygears
Senior Member
Posts: 1396
Joined: Tue Feb 05, 2013 12:25 am
Bikes: 1950 panhead, 1999 FLHTCI, 1987 FLHTC custom
Location: Daytona Beach
Has thanked: 438 times
Been thanked: 648 times

Re: Panhead lost compression

#8

Post by Andygears »

melvinjo wrote: Sun Jun 13, 2021 5:08 pm 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
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
Edaddy
Member
Posts: 102
Joined: Tue Dec 05, 2017 8:49 am
Bikes: 1965 Panhead
1992 Jammer frame
43" Custom Springer
1991 Std Case
STD dual-plugged heads
Location: Bellingham wa
Has thanked: 9 times
Been thanked: 21 times

Re: Panhead lost compression

#9

Post by Edaddy »

melvinjo wrote: Sun Jun 13, 2021 5:08 pm 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
Checked stone cold before disassembly. All good
Edaddy
Member
Posts: 102
Joined: Tue Dec 05, 2017 8:49 am
Bikes: 1965 Panhead
1992 Jammer frame
43" Custom Springer
1991 Std Case
STD dual-plugged heads
Location: Bellingham wa
Has thanked: 9 times
Been thanked: 21 times

Re: Panhead lost compression

#10

Post by Edaddy »

pan620 wrote: Sun Jun 13, 2021 1:09 pm
Edaddy wrote: Sat Jun 12, 2021 3:52 pm Solid lifters. Awesome thanks for the response. I will clean it up and put it back together and test.
I think you need to figure why this happened, just cleaning it up will produce the same results.
My Mikuni carb needs replaced. I have parts for an SU carb and may put it on at reassembly.
awander
Senior Member
Posts: 2082
Joined: Fri Sep 21, 2007 3:03 am
Bikes: '52 FL
'64 FLH
Has thanked: 163 times
Been thanked: 511 times

Re: Panhead lost compression

#11

Post by awander »

Edaddy wrote: Mon Jun 14, 2021 2:39 am
melvinjo wrote: Sun Jun 13, 2021 5:08 pm 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
Checked stone cold before disassembly. All good
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.
blewcrab
Member
Posts: 301
Joined: Mon Jul 09, 2012 11:08 pm
Bikes: 65FL and 2003 heritage
Location: Southern Maryland
Has thanked: 90 times
Been thanked: 41 times

Re: Panhead lost compression

#12

Post by blewcrab »

jus a thought ....make sure you adjust valves to solid spects ....dont adjust according to hydraulic spects
Post Reply

Return to “Panhead”