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Old 04-19-2019, 08:25 AM   #1
[JP]
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Default Panhead compression... still chasing potential problems..

Hi...again.. yes it's me

Gearbox fixed.
Started the Pan, all good, starts as easy as she always done, 2nd or 3rd kick even when cold. Hot it's a first kick start.

My on/off switch is just under the coil and when I reached to switch her off I felt some air on my hand. Thought it was the rear exhaust.
But on close inspection it felt like it was coming from the head. - head gasket??

So, set out to check head bolts torque settings. Supposed to be 65ft lbs right?
Well.. all of them needed tightening up a bit.

Done that. started her again - she was warm, 1st kick start.
But the air leak was still there.

Did a compression test.
with wide open throttle right?

My results were 60psi on the front, 50psi on the rear.

Seems pretty low right? should be around 100psi or more?
Now, if these values are low... could this be the explanation, or the reason, as to why I broke down after 100 mile highway cruising? she shut off as I came off the throttle to slow down - but then started again after 1h, to then happen the same just 10 miles further on the highway.

thanks!

EDIT: just for kicks I got the plugs out of my shovel and tested it. got similar results. 75 on front, 65 on rear. Maybe the gauge I have is crap..?? it's new, but it's nothing fancy and expensive.
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Old 04-19-2019, 09:14 AM   #2
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Default Re: Panhead compression... still chasing potential problems..

WOT when testing?
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Old 04-19-2019, 09:29 AM   #3
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WOT when testing?
Yes WOT.
Kicked a few times till needle didn't move anymore.

Haven't done it with squirting oil in the bores though.
Apparently that increases compression a bit with oil sealing better.
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Old 04-19-2019, 09:41 AM   #4
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This is making me paranoid.
On close inspection it looks more like theres an exhaust leak on the rear and the air is traveling through the fins and blowing near the head bolt on the other side.

I'm double checking timing etc. As again, I'm paranoid and check shit like that a million times....
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Old 04-19-2019, 12:01 PM   #5
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Default Re: Panhead compression... still chasing potential problems..

You could also do a poor man's leakdown before deciding to pull the heads . . .

- remove timing plug & spark plugs
- open carb to WOT and secure throttle (or just remove carb)
- open pushrod tubes (no need to remove)
- engine at TDC compression on FRONT
- apply some compressed air to the FRONT cylinder

How to interpret results . . .
- hissing/airflow at the timing plug: rings leaking
- hissing/airflow at the exhaust: exhaust valve leaking
- hissing/airflow at carb/manifold: intake valve leaking
- hissing/airflow at pushrod exit on head: valve guide(s) leaking

Repeat for REAR cylinder.

You can back up your finding with the teaspoon of oil method. You may see less leakage at rings and more at valves/guides.

Let us know what you find.

Jason
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Old 04-19-2019, 12:05 PM   #6
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Default Re: Panhead compression... still chasing potential problems..

If it is only an exhaust leak, fix that as best as you can and ride it.

Basic four strokes suggest that compression is a must to have combustion. It is wellknown that there must be enough of it to get full combustion. IF you are not fouling plugs and the tune is right..... well Bob’s your uncle.

Get a leakdown tester and borrow another comp tester and have a buddy help. My bet it its fine. It starts easy and aint smokin...right?
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Old 04-19-2019, 01:08 PM   #7
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I have same issue, bike starts and runs fine but poor figures. Going to try pushing it rather than kicking when I get a chance. How many licks did you give it?
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Old 04-19-2019, 01:09 PM   #8
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Default Re: Panhead compression... still chasing potential problems..

Quote:
Originally Posted by [JP] View Post
Yes WOT.
Kicked a few times till needle didn't move anymore.

Haven't done it with squirting oil in the bores though.
Apparently that increases compression a bit with oil sealing better.
This is the next step. Wet compression will help you determine if the rings are not sealing or if the problem is in the valvetrain.
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Old 04-19-2019, 01:10 PM   #9
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Default Re: Panhead compression... still chasing potential problems..

Quote:
Originally Posted by [JP] View Post
This is making me paranoid.
On close inspection it looks more like theres an exhaust leak on the rear and the air is traveling through the fins and blowing near the head bolt on the other side.

I'm double checking timing etc. As again, I'm paranoid and check shit like that a million times....
I'll cross Jaws on this one and say this is still a problem. An exhaust leak won't give your shit compression numbers.

Why is your compression so low? That would be something I personally would be very curious about were that my Pan.
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Old 04-19-2019, 02:15 PM   #10
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Quote:
Originally Posted by JasonMcElroy View Post
You could also do a poor man's leakdown before deciding to pull the heads . . .

- remove timing plug & spark plugs
- open carb to WOT and secure throttle (or just remove carb)
- open pushrod tubes (no need to remove)
- engine at TDC compression on FRONT
- apply some compressed air to the FRONT cylinder

How to interpret results . . .
- hissing/airflow at the timing plug: rings leaking
- hissing/airflow at the exhaust: exhaust valve leaking
- hissing/airflow at carb/manifold: intake valve leaking
- hissing/airflow at pushrod exit on head: valve guide(s) leaking

Repeat for REAR cylinder.

You can back up your finding with the teaspoon of oil method. You may see less leakage at rings and more at valves/guides.

Let us know what you find.

Jason
Thanks!
What do you mean apply air to front cylinder, what's the procedure here?
Stick air through where?

Quote:
Originally Posted by JAWS View Post
If it is only an exhaust leak, fix that as best as you can and ride it.

Basic four strokes suggest that compression is a must to have combustion. It is wellknown that there must be enough of it to get full combustion. IF you are not fouling plugs and the tune is right..... well Bob’s your uncle.

Get a leakdown tester and borrow another comp tester and have a buddy help. My bet it its fine. It starts easy and aint smokin...right?
Well no she doesn't smoke. Well she does when she's cold, you try blip the throttle and she doesn't like it.. Coughs a bit..etc.. But after that she's fine. Rides fines too.
And it's dead easy to start.

Quote:
Originally Posted by CookieMonster View Post
I have same issue, bike starts and runs fine but poor figures. Going to try pushing it rather than kicking when I get a chance. How many licks did you give it?
I gave it about 5 or 6 kicks?
Done it till the needle stopped going over. Maybe a bit more than 6
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Old 04-19-2019, 02:17 PM   #11
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Quote:
Originally Posted by govmule84 View Post
Quote:
Originally Posted by [JP] View Post
This is making me paranoid.
On close inspection it looks more like theres an exhaust leak on the rear and the air is traveling through the fins and blowing near the head bolt on the other side.

I'm double checking timing etc. As again, I'm paranoid and check shit like that a million times....
I'll cross Jaws on this one and say this is still a problem. An exhaust leak won't give your shit compression numbers.

Why is your compression so low? That would be something I personally would be very curious about were that my Pan.
Yep I'd like to know too.
Was pure chance I felt the air on my hand as I reached for the switch.
But I reckon that air I felt is coming from the back of the rear exhaust where its not sealing properly despite my efforts of playing with bracket locations.

Then I got the compression tester out. Brand new.. Bought it a couple of weeks ago as was on offer and thought would be handy.
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Old 04-19-2019, 03:45 PM   #12
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Default Re: Panhead compression... still chasing potential problems..

Quote:
Originally Posted by [JP] View Post
Thanks!
What do you mean apply air to front cylinder, what's the procedure here?
Stick air through where?
You apply the air to the cylinder through the spark plug hole . . . and see where it comes out.

Jason
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Old 04-19-2019, 05:17 PM   #13
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Quote:
Originally Posted by [JP] View Post
Thanks!
What do you mean apply air to front cylinder, what's the procedure here?
Stick air through where?
You apply the air to the cylinder through the spark plug hole . . . and see where it comes out.

Jason
Ah right. That's what I thought.
Guess I'll have to adapt some sort of thing.
Maybe use the adaptor on the compression tester and put the air compressor gun on it..
I'm guessing it has to build pressure in it.
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Old 04-19-2019, 05:47 PM   #14
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Default Re: Panhead compression... still chasing potential problems..

It really doesnt take much pressure. Make sure its at TDC. For the leakdown test.

Compression readings at a minimum of 90 psi as a general rule for combustion. Generally lower and they wont start well and will have low power and usually smoke alot.
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Old 04-19-2019, 05:53 PM   #15
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Default Re: Panhead compression... still chasing potential problems..

I have seen as low as 80 psi on a good runner. But the running comp readings were higher. I blame overlap for the low static numbers
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Old 04-19-2019, 05:55 PM   #16
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Default Re: Panhead compression... still chasing potential problems..

Put your comp gauge in one hole and fire it on the other. What do you get then. On some gauges you must remove the core in the hose if it has one, to do a running test. The needle will bounce.
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Old 04-19-2019, 07:08 PM   #17
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Default Re: Panhead compression... still chasing potential problems..

China tester?
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Old 04-20-2019, 10:47 AM   #18
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Default Re: Panhead compression... still chasing potential problems..

Haven't done the tests asked for, apologies.
I wanted to take her out to test the new bushes on the suspension and how my god what a difference! I'm actually surprised on how much better she is, makes me want to go faster! ahaha, corners like it's on rails.

But, as I was going out, I made a little video just to show that despite the shit compression, she's easy to start.
here's a video on cold, just rolled it out the garage.


and.. about 15 miles after, happily idling. No smoke, nothing major.
only thing that happens now and again is revs stay high for a while when I stop. probably an intake leak somewhere?

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Old 04-20-2019, 12:18 PM   #19
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Default Re: Panhead compression... still chasing potential problems..

How does a Portuguese madman trapped in England accumulate so much cool old American iron?
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Old 04-20-2019, 01:32 PM   #20
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Default Re: Panhead compression... still chasing potential problems..

Considering it starts so easily and rides and runs.

As has been said anything below 80 PSi doesn't start well!
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