V-Twin "Replica" Pan Heads

[panhead_kicker]

... I seem to have lost a lot of compression in the front cylinder...

Do you plan on identifying the leak, before tearing it down?

[Mongrel505558]

... I seem to have lost a lot of compression in the front cylinder...

Do you plan on identifying the leak, before tearing it down?

Yes. I just ordered a leakdown tester. Should have it by the weekend. Adding oil in the spark plug hole didn't change my compression readings and just created a lot of smoke when I fired the motor up after.

[Panacea]

I used to screw an air fitting into the spark plug hole, Make sure both valves are closed, pump it up (make sure the brake is locked) then listen for where the air is escaping, timing plug hole? exhaust pipe? carb intake? You could even squirt some soapy water around the head gasket to look for bubbles...Mike

[Mongrel505558]

I used to screw an air fitting into the spark plug hole, Make sure both valves are closed, pump it up (make sure the brake is locked) then listen for where the air is escaping, timing plug hole? exhaust pipe? carb intake? You could even squirt some soapy water around the head gasket to look for bubbles...Mike

Yeah, I was thinking about putting something together without the gauges for a quick listening for air test. I may possibly have a burnt front exhaust valve, because when I ran the motor after the compression test with oil in the cylinder I was getting smoke around the front exhaust port as well as out of the pipe. An exhaust leak here could burn a valve. But I still want to do the leakdown test before I pull the head.

PS. Awander, I wasn't intending to hijack your thread.

[Panacea]

as I recall an ordinary air fitting like you would use on an air hose to tire chuck fits right into the spark plug hole, it's the wrong thread but all you need is one thread with some teflon tape to make a decent seal good enough to hold ten pounds or so, your milage may vary...

[Mongrel505558]

as I recall an ordinary air fitting like you would use on an air hose to tire chuck fits right into the spark plug hole, it's the wrong thread but all you need is one thread with some teflon tape to make a decent seal good enough to hold ten pounds or so, your milage may vary...

Just did what you suggested with the quick connect fitting and teflon tape and it worked like a charm. Only hard part was keeping the bike from moving. Hard to hold the brake pedal while listening around the bike from different vantage points. The result is at about 10 psi I had substantial leakage through the front exhaust valve. I could hear it and feel it from the front exhaust pipe. Also a little from the timing inspection hole, but I'm not going to worry about that since I hadn't warmed up the bike before testing. I guess it's time to pull the head and lap or replace the front exhaust valve. Also have to look at better sealing at the front exhaust spigot.

[awander]

push the front tire up against a wall

[RooDog]

Any applied air pressure is going to drive the piston down. Best practice would be to remove the push rods, letting the valves seat, and just don't fight the engine from turning til it hits BDC, then listen for leakage. Anything else is just bringing on frustration....
....RooDog....

[Mongrel505558]

Any applied air pressure is going to dri ve the piston down. Best practice would be to remove the push rods, letting the valves seat, and just don't fight the engine from turning til it hits BDC, then listen for leakage. Anything else is just bringing on frustration....
....RooDog....

I wish I'd thought of that. Makes perfect sense. With pushrods out it shouldn't even make any difference whether I'm at TDC on that cylinder or not. I ordered a "real" leakdown tester yesterday with two 100 psi gauges to measure percent. In the case of this cylinder I only needed my ears to tell me the exhaust valve wasn't sealing, but I have other bikes and I'm sure the tool will be put to use.

[RooDog]

Any applied air pressure is going to dri ve the piston down. Best practice would be to remove the push rods, letting the valves seat, and just don't fight the engine from turning til it hits BDC, then listen for leakage. Anything else is just bringing on frustration....
....RooDog....

I wish I'd thought of that. Makes perfect sense. With pushrods out it shouldn't even make any difference whether I'm at TDC on that cylinder or not. I ordered a "real" leakdown tester yesterday with two 100 psi gauges to measure percent. In the case of this cylinder I only needed my ears to tell me the exhaust valve wasn't sealing, but I have other bikes and I'm sure the tool will be put to use.

I bought a leak down tester off the Mac Tool Truck more years ago than I care to remember, only tried it one time and it drove the bike. And that's when I learned that the PRs need to be out. Pressure will rotate the engine anywhere you put it except dead nuts on TDC, and of course BDC....
Surface area of the piston is about 7 square inched, X 100# is a lot of pressure it retain....
Best wishes.... RD....

[melvinjo]

I bolted mine on right out of the box. I think they are good build and quality, and thats with about 2K miles on them now

[Mongrel505558]

I bolted mine on right out of the box. I think they are good build and quality, and thats with about 2K miles on them now

I did the same, and all was great for a while. Then I took them off to re-seal the pan covers and found a broken outer valve spring on one of the heads. I'm running an Andrews J grind cam so there no crazy lift or other abuse to the valve train. Changed all the valve springs out and got rid of the orange painted springs that came with the heads. The motor has been running great since until it suddenly lost compression in the front cylinder. Still runs great, but I'm not letting this condition go on.

I agree with you about quality in terms of the castings and machining, but after the broken valve spring in less than 50 miles and a valve going away on me now after about 600 miles I just don't trust the valve gear they came assembled with. I'm definitely changing out the front exhaust valve for a Black Diamond or Manley, and probably change the intake while that head is off. This winter I'll probably change the rear head valves as well.

Jim

[Panacea]

Did that valve fit the guide and seat well after the spring was replaced?

[awander]

id that valve fit the guide and seat well after the spring was replaced?

Mine did, but I recut the seats and reground the valves to get rid of the overlap interference I had, because of my cam.

[RooDog]

Did that valve fit the guide and seat well after the spring was replaced?

If the assembly is within OEM specs, what would the springs have to do with those parts? Just wondering if there is something I am not aware of....
....RooDog....