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Old 04-26-2019, 02:51 AM   #61
[JP]
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Default Re: Panhead compression... still chasing potential problems..

No I haven't done compression tests anymore.
done all those tests yesterday and then left it, waiting for feedback from here.

I haven't taken the intake off, I only took the front pot clamp off so I could see the bubbles.
Intake maniford and carb are still there. Air cleaner is off.

When I listen in the carb there's no change in sound when I open and close the throttle.
I can hear air, but I think this is the air I can hear in the heads.
it kind of resonates everywhere...

But the question still on my head, after all these tests, is:

Head gasket is ok - no bubbling anywhere
Valve seats seem ok
Air going through pistons but you say a little is ok.

I'm losing 5psi....

where's the explanation to why my compression test results being so low?

It's a strange one? maybe there wasn't any problem to start with? which considering the bike starts fine, runs fine, doesn't smoke.....means everything was ok?

Over the weekend I'm taking the exhausts off, do the leak down tests again.
Have to take the exhaust anyway because I want to seal them properly.
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Old 04-26-2019, 10:41 AM   #62
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Default Re: Panhead compression... still chasing potential problems..

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Originally Posted by [JP] View Post
I can hear air, but I think this is the air I can hear in the heads.
it kind of resonates everywhere...

I'm losing 5psi....
Stick the hose to one of your ear's and the other end to what you want to listen to. No distraction only hear what you have the hose at.

At what inlet pressure are you losing 5 psi?
25 psi that's 20% bad, 50 psi that's 10% OK, 100 psi that's 5% almost to good to be true.


Also leak down tests are done on a warm engine, usually. Idea being knowing the loss when running not starting. More loss cold makes kicking easier. One more thing when you have the engine at top dead and have the air on you should move the crank shaft back and forth to allow the air pressure to seat the rings.
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Old 04-26-2019, 12:01 PM   #63
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Default Re: Panhead compression... still chasing potential problems..

HI,
on post #56 has all the values there and my procedure, not sure if you seen as it's on the page before this one.
I was losing 5 psi at around 60/70psi, my compressor can't really kick much out, well it can, I think I managed to get 90 psi, maybe around there I'm losing 10 psi, once it gets to 75, there's a 5 psi difference on gauges. and once it gets to around 50s the gauges are the same.

I just had a little bit of time in the garage.
Still with pushrods completely loose, now I have taken the exhausts out, both of them.

Pushed air in again, I get bubbles if I put my hand and soapy water on the exhaust port - so I'm guessing the valves not sitting properly. both front and rear



Doing this with a warm engine will be nearly impossible, well... not at the stage i'm at now, with pushrods collapsed, exhausts out, etc...

I'm not really sure what to do now.
Head gasket seems to be fine, there's no bubbles whatsover, and from what I can hear the air is escaping through the exhaust valve and I can hear it coming out the pushrod holes in the heads.

But.. bike starts, runs fine, doesn't smoke.

What should I do? I'm half tempted to just put it all back together and ride. She was fine... before, if it wasn't for me to feel that puff of air on my hand (which more than likely was coming from a not properly sealed exhaust on the rear manifold) I would have never been investigating this far.
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Old 04-26-2019, 02:13 PM   #64
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Default Re: Panhead compression... still chasing potential problems..

That gets my vote. Why torture yourself over an issue that won't abruptly leave you at the side of the road ... or do any slow but serious damage that I can think of*?

* My usual disclaimer applies here.
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Old 04-26-2019, 02:19 PM   #65
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Default Re: Panhead compression... still chasing potential problems..

Well... she did broke down on me in October. after 100 miles of highway riding she cut off when I slowed down... eventually managed to start her after 1h, to then the same happen 15 miles ahead.... but only cut out when slowing down.

I doubt any compression problems would have manifest like that? specially when now she's been riding fine, and the only thing I changed since then was a very very corroded battery terminal...

btw.. i'm not sure if you are being sarcastic? hahaha
I would like to know why the so low compression values.... but then again when I tried on my shovel it had the same values...and that runs like a champ too.

damn bikes. lol
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Old 04-26-2019, 04:20 PM   #66
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Default Re: Panhead compression... still chasing potential problems..

5psi is fine. Im gonna stand by what I said many posts ago. She starts easy and dont smoke. The tune is good and it runs good.

There is such a thing as low compression engines.

As far as gauges go.... there is a reason why in aircraft the instruments all point straight up in “normal” operation. For quick reference if somethings goes array its easy to find. I have seen temp and pressure gauges be 40-50 degrees or 20-30 psi different on the same application. Same engine, same operation conditions. A gauge is just that, a gauge to reference “normal” or “standard”.

I have a cool little tool for electric gauges that is a bank of trim pots. I can mimic a sending unit and figure out what resistance range a gauge needs to show propperly in a given installation.

What was the difference in readings from your comp gauge and your buddies? If I recall they werent exactly the same...
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Old 04-26-2019, 04:33 PM   #67
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The difference with my friends gauge wasn't that great.. Basically the same. Less than 5psi difference if I remember correctly...

Guess tomorrow I'll be putting it all back together....

Have a bunch of stuff to do besides this.
Fit the new bearings for the 21, that arrived today and suit the 5/8 axle
Make new spacers for it, make an internal spacer for the invader.
Make a sissy bar extension so it's longer and I can strap by bag to it
Make a bracket of some sort to fit a left saddlebag to carry my tools for the trip...
Lots...
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Old 04-26-2019, 05:22 PM   #68
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Default Re: Panhead compression... still chasing potential problems..

Quote:
JWAS wrote:
I have a cool little tool for electric gauges that is a bank of trim pots. I can mimic a sending unit and figure out what resistance range a gauge needs to show propperly in a given installation.
Outstanding idea and easy to copy!
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Old 04-26-2019, 07:08 PM   #69
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Default Re: Panhead compression... still chasing potential problems..

No sarcasm here.
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Old 05-06-2019, 01:18 AM   #70
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Compression tested again just for kicks. Same low values.
She still starts first kick.. Cold or hot.. And rides and sounds like this.

Meh.... Europe trip in a week.. I'm taking her with me and hoping for the best.

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Old 05-06-2019, 10:45 AM   #71
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Default Re: Panhead compression... still chasing potential problems..

Yup. Ride it.
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Old 05-16-2019, 08:21 AM   #72
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Default Re: Panhead compression... still chasing potential problems..

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Compression tested again just for kicks. Same low values.
She still starts first kick.. Cold or hot.. And rides and sounds like this.
Bottom line, it sounds like the bike runs as well as any panhead, so I'd say enjoy the bike the way it is, and when you are REALLY ready go down the rabbit hole, then you can pull the top end and plan to have to have the bike down for a little while and spend some $. Because I have a feeling it'll snowball quickly and you might as well freshen up everything at the same time, assuming you don't take a piecemeal approach.
  1. Compression test- I'd stop worrying about the specific numbers. It sounds like it runs good and there's nothing alarming that i've read. This all started with you searching for an suspected leak. My opinion on kick only compression tests is to take them with a grain of salt. I'd mainly be concerned with a large discrepency between 2 cylinders. Aside from the fact that your kicking it over vs. a starter motor spinning the motor quickly and multiple revolutions, there's a myriad of variables cam overlap, bore, and variety of piston compression options.
  2. bubbles at intake- i'd bet dollars to donuts that the head has replaced valve seats. And what you'd find is a small hairline crack from the seat to the headbolt insert, then running up along that machined edge of the intake (where you saw your bubbles). I've had this, and it was minor enough that I just left it until such time as i was ready to do EVERYTHING in the heads, because this is definitely a pandoras box issue.
  3. bubbles at the exhaust port- the valve may not be seating well (ever or just as time's gone by from wear and pitting pitting). And if you do have replacement seats, that may factor in here as well.
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