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Discussion Starter · #1 ·
I've been fightin a rear pan cover leak so bad that you can hear it hiss & snivel every time I kick it over, like there's air pressure building up under the pan cover. It's in the middle of the rear pan, at the back (bottom), right infronta the seat post.
Pulled the heads - no cracks, the head's flat, and just to be sure I helicoiled all the pan screws. I'm usin thick D-rings with these gaskets: http://www.realgaskets.com/files/popups/popup9.htm (BTW, I think these may be the same as the Accurate Engineering ones). Put it all back together, makin sure the pan gaskets squished evenly, and there was absolutely no change in the leak.
Never had the slightest leak on the front pan or anywhere else on the engine.
The breather gear is timed right - I've checked and double checked. Case breather is vented with a hose out to the rear chain. But somehow I'm convinced this is more than a garden variety pan leak and that I'm gettin case pressure up inside the rear pan. Also, when I first built the motor, I lost my oil tank cap (push-in type) on the maiden voyage, like there might have been air pressure buildup in the tank.
Any ideas? This is drivin me crazy. And before I pull the heads or motor again and throw some new gaskets and sealer at it, I wanna know if this air pressure in the top end is normal or something to worry about. Thanks!
 

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This is interesting. I have a cone shovel bottom that I put NEW STD heads on, NEW D-rings, and NEW steel rocker covers. I was running the thick steel/rubber gaskets, but had a leak on both heads in a corner of each, so I replaced them with the thick cork gaskets.

I still get alittle seepage from the cork gaskets, but nothing major like before. But I have noticed a "hiss" if I have to kick it several times. I was trying to write it off on the commpression releases I have in the plug holes that I'm not using (dual plug heads) But this has me thinking now.

I'd like to get a set of the cast pan covers to ensure a flat surface, the cheap steel pan covers might not be completely flat. Again, my heads are new, and the guy that built them for me is super anal, so I know they are set up right. Runs like a raped ape, and only "hissis" if It doesn't fire right up and I have to kick it over and over.

Sixball
 

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Have you made sure the breather passage is clear all the way out? If it's clogged that will cause a problem regardless of breather timing. If the rings are done the resulting pressure could overwhelm and come up through the drains to pressurize the pans. Like Skibo said a leakdown will answer many questions.
 

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Just a WAG, but have you checked to make sure the oil tank's venting properly? I'd think that it would evenly pressurize the motor if not, but I've seen stranger things happen...

-Kuda
'49 panchop
 

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There is also the painful but possible chance that the head is cracked from the chamber through to the top. I have seen various year Pans with cracked heads.
Robbie
 

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You said the case breather is vented with a hose to the rear chain, assuming you still have a cast oil pump, there is a screw on it that regulates the case breather. You might have it screwed in too far?
 

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there is a screw on it that regulates the case breather.
That screw regulates the CHAIN OILER, not the breather. The breather is unregulated and needs open access to the atmosphere.
Robbie
 

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Discussion Starter · #10 ·
Thanks for all the suggestions guys, but I gotta ask you to keep em comin...
I did a leakdown check before I pulled the heads - something like 12% on the front and 15% on the rear, cold. While the heads were off, I eyeballed the hell out of em for cracks (& yes, there's a minor crack the the plug hole, but nothing I haven't seen on other panheads), lapped the valves and installed valve guide seals. And I went ahead and pulled the jugs, honed the cylinders just a bit and re-ringed it. I haven't tested the leakdown since I've had it back together, but get this...she hisses & snivels even when the plugs are out. So I gotta think it's not compression pressure, but case vent pressure. I've also taken the breather vent hose off, to make sure it's not plugged. Seems to breathe through the case fine, with or without the hose. Kuda, maybe yer onto somethin...how would I check to see if the oil tank's venting like it should? I run hard lines, with an external filter...the oil tank vent line's goin to the right case vent. My oil pump's an early pan cast iron one, but with the later flat outer plate (no governor). I run a belt drive, and I wound up pulling the pump and welding up the rear chain oiler hole, cuz I could never get it to shut off - I always had a steady drip out the breather. The pan leak didn't get any better or worse after that, but I suspected too much case pressure back then, too.
Oh, and I forgot to mention it's a '49...so it oils through the cylinders and on up to the rockers...looking at the "Early" oiling diagram in my old Panhead Service Manual I can't tell what, if anything, would keep the case vent air from goin up the oil passage in the rear cylinder....hmmmm....maybe it's normal, except for the massive leak???
Thanks again guys, I need all the ideas I can get!!!
 

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...how would I check to see if the oil tank's venting like it should? I run hard lines, with an external filter...the oil tank vent line's goin to the right case vent.
The easiest way is compressed air. Pull the lines off both sides, pull the oil cap, and blow air in to the tank and (*gently*) the motor to see if you've got good breathing. I've even seen an aftermarket tank that had a little elbow facing down into the tank on the vent line. Strangely, when the motor was running fast enough the return couldn't keep up with the feed and the level built up in the tank, effectively blocking the vent line. So he's tooling along at 70 mph and suddenly it's the Exxon Valdez. Shut it all down and everything checks out fine. We ended up swapping a new oil tank in and everything was good. On yours, I've gotta suspect it's either a clogged vent line, something wrong in the tank, or (and this one scares me) somehow when you welded up the chain oiler it somehow f'd up one of the passages in the pump. Just something to think about...

-Kuda
'49 panchop
 

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Discussion Starter · #12 ·
Thanks Kuda, I'll check it out and get back to ya. I'm not losin sleep about the oil pump though; it was snivelin before I welded up the chain oiler. In the meantime, if you get really bored, check out the early oiling diagram and let me know if yer seeing something I'm not about the case vent air - what keeps it from goin up through the rear jug and head?
 

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Discussion Starter · #14 ·
OK, last night I started strippin the motor to pull it out and re-gasket the pans. With the generator off and the plugs out, I turned it over a few times. I could hear air moving (or trying to move) through the cam cover at the same intervals there was air hissin outta the rear pan....you'd think the bigass generator hole in the case would be the path of least resistance, right? WTF?
 

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Old school test for leaking heads. Make a fitting to connect shop air to the rear cylinder. Put piston at bdc, and apply 150 lbs of air pressure(or what ever you have available) and stick your ear next to the generator opening. If it is more than a slight hissing, you have a head leak/head gasket leak. Or even a bad piston, cracked or bad casting allowing cyl pressure to pressurize the crank case. The ring gap, can cause the same thing. But a leak down test should tell you about that, not to mention a compression test. If you reringed it, and the gap is to big, this could be the problem. I am assuming that you have the correct gasket, installed correctly on the base of the cyls. I would try the same thing, with less pressure, and with a blower nozzle, to test the crank vent, listening at the gen hole again. It should do more than hiss, which is normal. Or even, remove the vent hose from the tank, and crank motor. If it is flexible, and has way to much pressure, it should coil and shake, like a snake(squirting air/oil, so be careful not to cover yourself with spray).
 

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Discussion Starter · #17 ·
Shov, I don't think it's blow-by or a head leak, cuz the plugs were out, so no real cylinder pressure...i'm thinkin the breather passage in the case or the cam cover may be garfed. I'm gonna try blowin through the breather (gently) tonight, but I'm not sure what normal is....should be pretty much wide open to come out through the generator hole via the case & cam cover passages, right?
 

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It should be way more than a hiss. If it does it with the plugs out, it has to be lower end crank case pressure. Are you sure that your breather in the cam chest is timed correctly?
 

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could be a clogged breather passage or if you have recentlly put on a new chrome cam cover some time the chrome will clog the breather passage in the cam cover and it will make the engine build up pressure

i saw one once was so clogged i put an air blower in the oil tank vent fitting on the case of the engine and it turned the motor over
 

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Discussion Starter · #20 ·
Let me begin by stating that I am, without question, an idiot.

I'm pretty sure the air movement I've been bitchin about is normal. I pulled both pans and turned the motor over. Lo and behold, I could hear air whooshing through both drain holes. The hiss & snivel action on the rear pan was just a bad leak. I think I've traced it down to a shitty pan cover - the left rear screw hole hangs over into the bend and allows air, oil and probably mid-sized SUVs a path from inside the motor, out through the screw hole, between the D-ring and pan cover, and all over my seat post.

I think the fix is: a.) get a good pan cover, but NOS ones in decent shape are the stuff of legend and myth these days, and I have no faith in finding a good aftermarket one, b.) build up the area around that screw hole with weld and lap it down flat, c.) ditch the rubber gaskets and get some that I can slather with gasket maker, or d.) put a glob of gasket maker on the screw before I stick it in. For the record, option d.) worked like a champ for me on an old pre-unit Triumph primary cover on which I had a similar problem. Since I am the buffoon who started this thread, I'll letcha know how it turns out. Maybe it'll help somebody else one day.
Thank you, everyone, for all the good suggestions.
 
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