Leakdown Test - Air Coming Out of Pushrod Holes in Head?

[Mongrel505558]

Turning my attention to solving my very low compression (30 psi) in my front head. Right now I'm performing another leakdown test. I definitely have a leak past my exhaust valve. I can hear that clearly through the pipe. Pushrods are out so valves should be closed. Negligible air from the timing inspection hole. I can't feel or hear air from there and I can thread the plug back in and the gauges don't change. But I'm hearing air escaping around the head and I can't place where from. To eliminate any sound from the leakdown tester regulator bleeding pressure off I took it out of the line and connected the tester quick-connect directly to my compressor. It's not a very big compressor so I have to keep the pressure down to around 20-30 psi or the compressor starts and I can't hear what I'm doing. I sprayed soapy water around the head gasket but didn't detect any leaks from there.

Anyway; what has me concerned is while chasing down the sound I stuck my fingers into the pushrod entry holes in the head and while the pressure is too low to feel anything, it stops the sound. It appears that I have pressure in the space above the head inside the pan. I'm trying to think of potential routes for air to get up in there. Please bear with me while I think out loud and feel free to offer suggestions.

Possibilities:

Ring blowby: seems to be minimal as described above. New pistons, rings, jugs fit to pistons, staggered gaps, about 300 miles on them. Rear cylinder perfect. Shouldn't the crankcase and area enclosed by pan be at the same pressure because they are connected by the oil return passage?
Head gasket: if blown between combustion chamber and oil feed or return holes. Should see same pressure as crankcase because of oil return passage.
Cracked Head: brand new V-Twin. Hope this isn't the case.
Porous Head: see above
Exhaust valve guide: either air getting past the valve and through the guide around the stem and through the stem seal (seems unlikely), or guide loose in head or some other problem in this area. Hopefully this is not the case. This is the valve that had the busted spring that I keep bitching about in the V-Twin heads thread, but when I reassembled with a new spring pair everything looked and felt alright. The inner spring was keeping the valve in place so nothing blew apart anywhere from the valve dropping.

I guess the next step is to pull the head and take it apart to inspect it. I need to do that anyway no matter what, and it will also allow me to get a look at my cylinder bore.

So do any of my ramblings make sense, or should I even worry about hearing air from this space? This would seem to explain why I can't completely prevent a pesky oil leak at the low point of the pan gasket. I know this is an imprecise method, but it's the best I have right now. I'm hoping I can lap my way out of this low compression problem, but at this point I really don't know.

Thanks in advance

Jim

Jim

[RooDog]

Jim....
I had to think on this a while, but then it hit me as I stepped into the shower this evening....
There are only three sources for leakage: The valves, how they are seating, should be zero leakage.
The head gasket. Again, zero leakage...
So that leaves only the rings, and the racers like less than 3% leakage there, Or a hole in the piston, from detonation.
So I suppose a tear down and a re-ring job is in order.....
What rings are you using?
....RooDog....

[nifty]

Hi Jim,
From memory this only started after the new heads went on and then only after the valve spring broke?

Max 30psi during leak-down test is a massive leak, plus at least 2 sources of leak

re ex valve leak to ex port: exhaust valve probably slightly bent due to inner spring not being enough to control valve i.e. with broken outer spring, slight valve over-shoot & whacked by piston. (also broken ends of spring may have overlapped and prevented full lift, at least check pushrod is still straight)
Could also be leaking behind valve seat (least likely, but possible)

re as described compression leak to pan cover chamber, should be detectable at timing hole, but can only be:
1. head gasket leak to drain or feed drillings (check cyl lip not bottoming in head)
2. porous/cracked head
3. porous/cracked piston (cracked piston could be related to bent exhaust valve)

Before you tear it down, squirt some light oil or similar into plug-hole and then re-do leakdown test, with luck you may see fluid leak source.

Cheers
Nifty

[Mongrel505558]

Jim....
I had to think on this a while, but then it hit me as I stepped into the shower this evening....
There are only three sources for leakage: The valves, how they are seating, should be zero leakage.
The head gasket. Again, zero leakage...
So that leaves only the rings, and the racers like less than 3% leakage there, Or a hole in the piston, from detonation.
So I suppose a tear down and a re-ring job is in order.....
What rings are you using?
....RooDog....

Rings are Hastings. Definitely leaking past exhaust valve. Teardown will probably happen tomorrow. What will I find? I'm hoping it's not the rings, since the jugs, pistons and rings are all brand new, with jugs fitted to pistons, and rings should be seated by now. The machine shop had the above parts for almost a year, so I really don't want to bring anything back to him during riding season. Machinist is very good and has done top end work for me before, and I trust the quality of his work. I know the rear cylinder rings are seated. Compression test shows 130 psi back there.

Jim

[Mongrel505558]

Hi Jim,
From memory this only started after the new heads went on and then only after the valve spring broke?

Max 30psi during leak-down test is a massive leak, plus at least 2 sources of leak

re ex valve leak to ex port: exhaust valve probably slightly bent due to inner spring not being enough to control valve i.e. with broken outer spring, slight valve over-shoot & whacked by piston. (also broken ends of spring may have overlapped and prevented full lift, at least check pushrod is still straight)
Could also be leaking behind valve seat (least likely, but possible)

re as described compression leak to pan cover chamber, should be detectable at timing hole, but can only be:
1. head gasket leak to drain or feed drillings (check cyl lip not bottoming in head)
2. porous/cracked head
3. porous/cracked piston (cracked piston could be related to bent exhaust valve)

Before you tear it down, squirt some light oil or similar into plug-hole and then re-do leakdown test, with luck you may see fluid leak source.

Cheers
Nifty

Nifty,
You are correct. This happened after the heads went back on with the valve spring replaced. Not immediately after, but within maybe a month. When I measured compression with the new heads on right out of the box I got 90 psi in both cylinders. I didn't retest until I noticed I could kick through the front cylinder compression stroke with very little resistance. That's when I measured 130 psi rear / 30 psi front.

Took pushrods out for leakdown test and then reinstalled them yesterday afternoon. All are straight. This weekend I'll find out what the exhaust valve, guide and seat, piston, etc., look like. Funny thing is when I first measured the low compression in the front pot I put some oil down the plug hole and repeated the test to see if the rings were the culprit, and I measured zero compression! I attribute this to something not right with the test, although I don't know what. I hold the throttle wide open and the gauge is good. I don't know. We'll see tomorrow.


Jim

[Mongrel505558]

Took my front head off yesterday and was happy to see the bore and piston looked fine. I poured some gasoline into the exhaust port and it flowed like a river past the valve. This is the valve that had the broken V-Twin spring. I lapped it a bit and couldn't get it to seal. I saw that the dull grey ring around the valve from lapping was thin in one spot, which suggests to me that the valve is slightly bent or at least the surface at this spot is further away from the seat - hence the thinner ring. I suspect this happened when the valve's outer spring broke. It looks like it kissed the intake valve. I checked the intake and it seals perfectly. I lapped in a different exhaust valve I had and it seals very well. With the head propped up and gas in the exhaust port I'll see a small drop leak through after about 5 minutes. I'm going out shortly to pull the springs to install a new seal and clean the pan gasket surface. Then I'll assemble the head and pushrods and do another compression test. I know a valve job is the correct way to go, but I want to ride this sucker while the weather is still good.

[Mongrel505558]

Motor is back together. Front cylinder now measures 95 psi on the compression test - up from less than 30 psi before the new valve. Left the top motor mount off and took the bike for a test drive. The power I'm used to is back. Letting it cool down before I retorque the head and then install the top motor mount. Then I'll relax before riding to a steak fry this afternoon.

Jim

[Panacea]

You would think there would be a mark left behind on the piston if the valve hit hard enough to bend itself...

[Mongrel505558]

You would think there would be a mark left behind on the piston if the valve hit hard enough to bend itself...

Luckily the valve never hit the piston because the inner valve spring didn't break. I had a seat drop once and it left a nice gouge in the piston, and bent the hell out of the valve, so I know firsthand what you're talking about. There does appear to be a small mark on the intake valve where I suspect the exhaust valve hit. Intake seals fine. The valve is not visibly bent, at least not at the stem. There is one spot, like a 5 degree arc, where the ring left from lapping is thinner, which tells me that spot is farther from the seat than the rest of the valve. It's more like the valve edge got deformed hitting the intake. My guess is it floated into the intake valve when it lost the outer spring pressure. Replacement valve left a nice even ring all around when I lapped it, so I guess the seat is okay.

[awander]

Glad you're back on the road!

[nifty]

Jim,
If the exh valve bent as a result of tangling with intake, I'm surprised intake is not also bent & leaking.

No way the bent ex valve leaking to ex port, even in conjunction with bad/non existent stem seal, could result in compression leak to pan cover chamber.
Pressure escapes via line of least resistance i.e. the exhaust pipe.
For the bent ex valve to be cause of compression leak to pan cover chamber, the exhaust port/pipe would have to be so restricted as to be virtually blocked off.
So why did you have air coming out of pushrod holes during leak-down test???
From what I understand of what you have described there is still an un-addressed underlying problem.

Nifty

[Mongrel505558]

Glad you're back on the road!

Thanks. Me, too.

[Mongrel505558]

Jim,
If the exh valve bent as a result of tangling with intake, I'm surprised intake is not also bent & leaking.

No way the bent ex valve leaking to ex port, even in conjunction with bad/non existent stem seal, could result in compression leak to pan cover chamber.
Pressure escapes via line of least resistance i.e. the exhaust pipe.
For the bent ex valve to be cause of compression leak to pan cover chamber, the exhaust port/pipe would have to be so restricted as to be virtually blocked off.
So why did you have air coming out of pushrod holes during leak-down test???
From what I understand of what you have described there is still an un-addressed underlying problem.

Nifty

My concern about air getting up into the pan cover chamber was that possibly my compression rings didn't seal. Air getting past them into the bottom end would also be present in the pan cover chamber because that volume should be at the same pressure as the crankcase due to the oil return passage connecting them.

I created some confusion for myself with this leakdown test because I got different results each time I tried it. I'll be the first to admit that it wouldn't pass scientific review. My compressor is too small in terms of capacity, so it has to run a lot to maintain pressure when it's called on to create any kind of flow beyond pumping up a tire. So I would run it to get the tank filled and then shortly after I got the regulator on the leakdown tester set to 100 psi the compressor would have to start again. And I can't hear anything else with the compressor running, which kind of defeats the purpose. I tried the test at lower pressures, but had the same problem. I haven't tried a leak down test since installing the new valve, and I suspect it might go better since I wouldn't have so much flow now that I have enough sealing to get 95 psi on a cold compression test.

This winter I'd like to replace the exhaust valve guide and have a professional valve job done to that head, but right now I'm within 10% compression between the two cylinders and the motor starts right up and runs great.

Jim

[RooDog]

Jim....
"the motor starts right up and runs great."
Good on you!
What more do we ask from our motorcycles?
....RooDog.....

[Andygears]

Hmmm, it seems through all this that the V-twin heads, while useable, are not the “My troubles are over” solution.

Poor quality control, in this case, the steel in the valve spring, has reared it’s head again. Very glad you got it fixed and are back together but consider if you had paid a shop for labor? And consider the shop, trying to make a few bucks selling and installing V-twin heads, the call-backs, diagnosis, accusations of over-revving, more parts, labor, delay with no running bike for the customer. How can a small shop stay in business with every portion of V-twin parts being suspected of poor quality and unknown failure?

My opinion of the bigger picture,
Andygears