Low Compression Problem.

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btperkins
Posts: 3
Joined: Sun Mar 21, 2010 5:02 am
Bikes: 1957 Panhead
Location: NW Indiana

Low Compression Problem.

#1

Post by btperkins » Mon Apr 05, 2010 10:08 pm

I'm new here folks, it's nice to meet everyone and perhaps you can give me some help? Back in the early 1970's I owned two Panheads, a 49 & 51. The 51 I rebuilt along with a total engine rebuild and increase to 80 C.I. I had a Tillitson carb and this was a one or two kick start machine. I was 22 at the time and married. Had to sell my machines when the kids came along or lose my home. I've never lost the longing for these spiritual machines! I'm now nearing 62 and just two weeks ago purchased a 57 Panhead on E-Bay. The seller indicated an engine, transmission and clutch rebuild 1000 miles ago. No paper work to verify this?! I can get this machine to try to start but it's very difficult. There are a number of things I've checked and looked at. I do have new manuals. I did a cold compression test twice on each cylinder. Back cylinder was 65 psi and the front was 63 psi. At four strokes both cylinders measured just below 50 psi. I did ten full strokes with the kicker to hit the 65 & 63 psi compression marks. The point gap I set at .022 and the S & S Shorty E is giving fuel. I cleaned the air filter and spark plugs. Both were fouled badly with oily carbon. Still I can barely get it to sputter. I spoke with a local H.D. dealer to have a certified mechanic come to verify these compression readings. There is no local dealer that has an old time mechanic that's qualified to look at this machine. I'm the best I have right now. I'm thinking if this engine was totally rebuilt and shows these very low compression readings something may be wrong with the sellers information? I've spoke to one internet mechanic that informed me that a cold compression is a valid way to check. He also told me that with readings as low as I'm getting he doubts this machine will run at all? Final decision was to totally rebuild a totally rebuilt engine? I'm not doing anything abrupt but I do have an investigation going on. Anyway, please have a look at my request here and tell me what you think about the compression information? Thank you for listening and any help you can throw my way.

Bill



PanPal
Posts: 1161
Joined: Wed Apr 21, 2004 8:57 pm
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58 FL
76 FLH All Original
Location: Maryland

Re: Low Compression Problem.

#2

Post by PanPal » Mon Apr 05, 2010 10:19 pm

Do you know if it has solid or Hydraulic tappets? Did you check you pushrod adjustment? There is a lot of good information in the knowlwdge base on this forum on adjusting both style tappets. Those S&S carbs have a tendency to flood easily.

partshunt
Panhead Register Member
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Joined: Sun Sep 24, 2006 9:04 am
Location: "Big Timber Country" Western Canada

Re: Low Compression Problem.

#3

Post by partshunt » Tue Apr 06, 2010 12:08 pm

Here is one suggestion of probably a lot you will get before this topic dies out. Any time you do a compression test, and especially if you question the readings. Oil the cylinders and do another "wet" test. If the compression improves, its ussually the rings/cylinder bore. If not, the valves are leaking or pinhole in the piston BUT! not likely both pistons. Valves care less when oil is added and it may be due to valve lash too tight (solids especially) or the valves are worn or burnt. You gotta start somewhere and culinder/valve condition needs to be determined before going deeper but 65 psi is enough to get her running I would suggest. Ebay engine can be a surprize sometimes........Joe

partshunt
Panhead Register Member
Posts: 305
Joined: Sun Sep 24, 2006 9:04 am
Location: "Big Timber Country" Western Canada

Re: Low Compression Problem.

#4

Post by partshunt » Tue Apr 06, 2010 12:19 pm

By the way, I forgot to mention, keep the throttle wide open when doing both your compression tests so the engine can swallow lots of air for max readings. You may know that but just trying to help a bit here...Joe

Bosheff
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Bikes: 65 FLH 82 FLH
Location: Michigan

Re: Low Compression Problem.

#5

Post by Bosheff » Tue Apr 06, 2010 1:20 pm

At 65 lbs. per cylinder, the rat that lives under the bench should be able to start the damn thing. While 65 lbs. indicates a tired engine to me it may or may not be valves, but I'm bettin on pistons and rings. I've owned more than just a few H-D's over the years and 90 percent of the ones I looked into buying that I did not know personally, were just "rebuilt." Some peoples idea of "rebuilding" is to polish the pan covers, replace the pushrod corks, and paint the cylinders. There's a reason people sell things on EBay. They cannot sell it locally, because everybody knows the machione and its history. This may not be what ya wanna hear, but more times than not, that's how it goes. If the unit in fact, was what it was presented as being, usually someone close to the seller will buy it. Still, at 65 lbs. it should run, but probably will leave alot to be desired performance wise. Pull the top, check the heads, mic the cylinders and pistons. This eliminates the guess work....bosheff

btperkins
Posts: 3
Joined: Sun Mar 21, 2010 5:02 am
Bikes: 1957 Panhead
Location: NW Indiana

Re: Low Compression Problem.

#6

Post by btperkins » Tue Apr 06, 2010 10:54 pm

Thank you all for your input. I did do the wet test with the throttle full open. The compression dropped down to 50 & 51 psi. I've received some good suggestions here and I'm learning. As far as rebuilt engines go I see many variations of the meaning. Trials fall into the path of learning but those lessons are well remembered. I'm happy to have this 57 Panhead and to be with a group of others willing to share their knowledge.

Bill

NightShift
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Bikes: Two Schwinns, a Hercules, and a Hiawatha
Location: Underground in Illinois

Re: Low Compression Problem.

#7

Post by NightShift » Tue Apr 06, 2010 11:41 pm

Dear Bill,
It doesnt take much compression to start. And once it does compression can come back.
Find out the other reasons it dont start.

Odds are heavy that its sucking air at the manifold. Almost a sure bet.

Hope to help,

fourthgear
Posts: 1390
Joined: Mon Apr 11, 2005 1:12 pm
Location: north florida

Re: Low Compression Problem.

#8

Post by fourthgear » Wed Apr 07, 2010 3:07 am

I agree with the above (air leak ). I would also check as has been said ,push rod adj. or lifters not pumping up, timing , bad coil ,bad condenser, bad fuel (old or contaminated )plugs or wires & points .
Any used HD I have bought ,that I did not know the history , I disassemble & inspect & thats why I have two good running Pan's . As said so well above , there idea of a rebuild ,may not be your or my idea of one .

Sir_Rat
Posts: 285
Joined: Sun Nov 01, 2009 10:10 am
Bikes: '37 UL, '79 Frankenstein, '88 Sporty
Location: Oahu Hawaii

Re: Low Compression Problem.

#9

Post by Sir_Rat » Wed Apr 07, 2010 10:59 am

OK here's my fifty cents:
An HD dealer who doesn't have a mechanic qualified to do a compression test? Bullshit!!! Cleaning the plugs doesn't mean they are firing well. Plugs are cheap try new ones, maybe a new condenser? Are the points pitted? Check for vacum leaks, I don't see how they could affect compression but they will sure make your bike hard to start.
I have never ever heard of compression going down on the wet test. Go up or stay the same...but go down??? Not saying it can't happen, but I've done my share of compression checks on both cars and bikes and I have never seen compression go down on the wet test. You got enough compression for that engine to run. The compression in the front and rear cylinders is roughly equal, thats good, or at least not bad. The best advice you got here was to go through the whole engine...thats the best you could do.
On the other hand....maybe you just want to try and trouble shoot instead. I would start off easy...pull the push rod covers and spin each one when its valve is closed, should spin straight and with a little drag on it. Find out if you got solids or hydralics and check the adjustment per the book or I'm sure its in the knowledge base here somewhere. The pushrods (Intake/Intake and Ex/Ex) should all move up and down the same amount. If you got Hydralics find out how to test them and also you might want to check to see if you got decent oil pressure. If can do a leak down test. If all is good there re-check the timing, If you got auto advance check the springs. If all is good there and it still won't run pull the timing cover and make sure all is well there....nothing broken/badly worn and the gears are timed right? Is the distributor set right? After that if it still won't start/run then you really got no choice but to open her up. Good luck!!

Hows that for fifty cents?? :D
Aloha ...Mike

partshunt
Panhead Register Member
Posts: 305
Joined: Sun Sep 24, 2006 9:04 am
Location: "Big Timber Country" Western Canada

Re: Low Compression Problem.

#10

Post by partshunt » Wed Apr 07, 2010 11:47 am

I agree, you should start with the simple items first. If the seller sez he rebuilt the engine, then who knows? maybe he did. Even if he only put in a set of rings on decent walls and tuned it up. If the tune up was good and if all else is good, its gotta run. You may have heard this term," always trace your problem thru, before deciding what to do".....I found that note many years ago on a sensor one day when a sharp guy found it at fault and all the other shops one by one changed the carb, another shop put in a new battery and the third shop sold him a distributor. And of course he paid each bill to bail the machine out and it still acted up till finally another sharp troubleshooter traced it to the sensor and tagged a note on it..........Joe

Ohio-Rider
Posts: 362
Joined: Tue Jan 25, 2005 3:04 pm
Location: North-East Ohio

Re: Low Compression Problem.

#11

Post by Ohio-Rider » Wed Apr 07, 2010 2:20 pm

Don't be concerned with the compression numbers until you get it running. Assuming you have good spark, start with a manifold test. Get used to doing this test because as a panhead owner you will need to check the manifold for leaks often. If even a tiny leak is found don't do anything else until all leaks are resolved.

Next thing is to go to S&S web site and download the instructions for returning the carb back to the factory settings and how to adjust it to your engine. Those S&S carbs can get way out of wack if tuned wrong. Often guys with manifold leaks make the mistake of trying to adjust the carb to the leak. That DOESN'T work. Good Luck and keep us posted. -Steve

Bosheff
Posts: 1223
Joined: Fri Jul 03, 2009 8:23 pm
Bikes: 65 FLH 82 FLH
Location: Michigan

Re: Low Compression Problem.

#12

Post by Bosheff » Wed Apr 07, 2010 2:26 pm

For the price of a couple of head and base gaskets and yer time, you can have it apart and can go from there. A person can spend an eternity speculating, but in a couple of hours you can know for sure. Besides, even if ya get it runnin, don't cha really want to know the mechanical state of the internals of yer mill? Don't ever depend on what the last owner tells ya, cause if it was as sweet as he claimed, he wouldn't have sold it in the first place!....bosheff

indianut
Posts: 161
Joined: Fri Aug 08, 2008 1:26 pm
Bikes: American
Location: Florida

Re: Low Compression Problem.

#13

Post by indianut » Wed Apr 07, 2010 4:35 pm

I have seen cams modified with so much overlap that you have Very Little compression. Remove your pushrods and kick it One Time. See if it feels like a substantial increase in compression. The first kick is the only one that counts because with no pushrods you will be drawing a vacuum on the second kick. It took me 2 years and several removals of the heads on a Panhead to figure out that some moron had re-ground the Sifton 412 cam causing this situation. When compared to an identical cam the lobes varied by .050!

PanPal
Posts: 1161
Joined: Wed Apr 21, 2004 8:57 pm
Bikes: 50 EL custom
58 FL
76 FLH All Original
Location: Maryland

Re: Low Compression Problem.

#14

Post by PanPal » Wed Apr 07, 2010 7:23 pm

I have seen cams modified with so much overlap that you have Very Little compression.
I wondered if this could be the case also. One of the pans I purchased had high compression pistons a big cam. It was a Sifton also, but it took nothing to kick it over. Now back to a stock FLH cam and low compression pistons I feel more compression when kicking. It ran hotter than it should before changing back closer to stock too.

chopped850
Posts: 59
Joined: Wed Mar 31, 2010 9:31 pm
Bikes: 1962 FL
Location: NW Indiana

Re: Low Compression Problem.

#15

Post by chopped850 » Thu Apr 08, 2010 11:36 am

Welcome to the board fellow hooiser. I might live in kalifornia but was born and raised in Michigan City/La Porte area. Anyway, you could also pull the distributor and turn it 180 degree's. It's about the only suggestion I haven't read yet.

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