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Proper way to test for compression?

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Old 10-12-2011, 01:22 PM
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Default Proper way to test for compression?

Hey guys,

I had SE-255 Cams installed recently and there's a chance they didn't get aligned properly, so I need to check compression to see if that's the case. I've read to remove both plugs and ground the plugs to the engine and also to remove the EFI fuse. Is this the correct method? Also, I looked at the fuse box diagram and all I could find was the fuel pump fuse...is the EFI fuse elsewhere or labeled something else? I plan on doing the test when I get home this afternoon, so any help or tips would be greatly appreciated!

Thanks,

Roger
 
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Old 10-12-2011, 02:51 PM
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I don't go to all that bother, really. plugs out, throttle open 6 hits on each cyl. should be even (within10-15 lbs of each other, which is actually a pretty generous spread for all you spec freaks!) and should be above around 150 psi or so. if you have the cam timing off, comp will be pretty low, and bike will be very low on power and should be hard starting. don't know mileage or year of bike, all that comes into effect as well. why don't you take it back to the guy who did it and have him recheck the timing?
 
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Old 10-12-2011, 03:50 PM
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Originally Posted by harleycharlie1992
...why don't you take it back to the guy who did it and have him recheck the timing?
If I were the guy who put the cams in and you came back to me saying that you suspect the cam timing is off, here's what I'd tell you...

I'm certain the cams are aligned properly. Alignment of the timing marks is something I'm always certain of when doing a cam swap. But if you want me to tear into it and double check I'd be happy to do that. You can even watch if you'd like.

If upon inspection the cams are aligned correctly you will pay for the inspection. If they are not, I will correct it and refund every penny you originally paid me in labor.

To the OP... Why do you suspect that the cams are out-of-time? I understand that mistakes are possible, but any competent technician should NEVER make that mistake.

Now if the cams or gears are misground and that is throwing the cam timing off, that's a whole 'nuther story.
 
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Old 10-12-2011, 04:37 PM
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Originally Posted by 2black1s
If I were the guy who put the cams in and you came back to me saying that you suspect the cam timing is off, here's what I'd tell you...

I'm certain the cams are aligned properly. Alignment of the timing marks is something I'm always certain of when doing a cam swap. But if you want me to tear into it and double check I'd be happy to do that. You can even watch if you'd like.

If upon inspection the cams are aligned correctly you will pay for the inspection. If they are not, I will correct it and refund every penny you originally paid me in labor.

To the OP... Why do you suspect that the cams are out-of-time? I understand that mistakes are possible, but any competent technician should NEVER make that mistake.

Now if the cams or gears are misground and that is throwing the cam timing off, that's a whole 'nuther story.
It's suspect because it was running perfectly before the cams. I had the cams and a power vision installed at the same time. The power vision is using a tune Fuel Moto said is tried and true. The bike is really hard to start and runs like crap once it's running...never evens out. Jamie is the one who suggested I check compression.
 
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Old 10-12-2011, 04:43 PM
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Originally Posted by TheBurninator
It's suspect because it was running perfectly before the cams. I had the cams and a power vision installed at the same time. The power vision is using a tune Fuel Moto said is tried and true. The bike is really hard to start and runs like crap once it's running...never evens out. Jamie is the one who suggested I check compression.
Did you try unplugging the PV and seeing if it runs ok? At least that way you have eliminated the PV from the equation.
Also, are the O2 sensors connected properly?
 
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Old 10-12-2011, 05:03 PM
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Originally Posted by uscanuck
Did you try unplugging the PV and seeing if it runs ok? At least that way you have eliminated the PV from the equation.
Also, are the O2 sensors connected properly?
I did not try unplugging the PV...it flashed the ECM, so I'd have to revert to stock tune first....which wouldn't run well at all since I have stage I upgrades plus the 255 cams...so I'm not sure that would help me diagnose the problem.

The O2 sensors looks to be connected properly, but they are the autotune ones which to my understanding aren't used to change anything on the fly.

I just went to check the compression and the compression gauge insert did not fit, it was too big. Anyone know what size I need for the bike?
 
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Old 10-12-2011, 06:00 PM
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Originally Posted by 2black1s
If I were the guy who put the cams in and you came back to me saying that you suspect the cam timing is off, here's what I'd tell you...

I'm certain the cams are aligned properly. Alignment of the timing marks is something I'm always certain of when doing a cam swap. But if you want me to tear into it and double check I'd be happy to do that. You can even watch if you'd like.

If upon inspection the cams are aligned correctly you will pay for the inspection. If they are not, I will correct it and refund every penny you originally paid me in labor.

To the OP... Why do you suspect that the cams are out-of-time? I understand that mistakes are possible, but any competent technician should NEVER make that mistake.

Now if the cams or gears are misground and that is throwing the cam timing off, that's a whole 'nuther story.
would not expect him to check timing, but I would expect him to see why its running bad, since he was the last one in. tag, you're it either the tune isn't right or possibly cam timing is off, one or the other, if he was paid to do the mods, he is responsible for the bike running properly after, unless he told the owner, before had that it wasn't going to work for some reason or another, this is a small modification, bike should run fairly well, op doesn't think its right, go back and let the tech tell him what is wrong
 
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Old 10-12-2011, 06:26 PM
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Have you checked the pushrods? Might have one or two out of adjustment, either hanging open or closed will make it run crappy.,,
 
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Old 10-12-2011, 07:04 PM
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Originally Posted by 2black1s
If I were the guy who put the cams in and you came back to me saying that you suspect the cam timing is off, here's what I'd tell you...

I'm certain the cams are aligned properly. Alignment of the timing marks is something I'm always certain of when doing a cam swap. But if you want me to tear into it and double check I'd be happy to do that. You can even watch if you'd like.

If upon inspection the cams are aligned correctly you will pay for the inspection. If they are not, I will correct it and refund every penny you originally paid me in labor.

To the OP... Why do you suspect that the cams are out-of-time? I understand that mistakes are possible, but any competent technician should NEVER make that mistake.

Now if the cams or gears are misground and that is throwing the cam timing off, that's a whole 'nuther story.
Originally Posted by TheBurninator
It's suspect because it was running perfectly before the cams. I had the cams and a power vision installed at the same time. The power vision is using a tune Fuel Moto said is tried and true. The bike is really hard to start and runs like crap once it's running...never evens out. Jamie is the one who suggested I check compression.
Originally Posted by harleycharlie1992
would not expect him to check timing, but I would expect him to see why its running bad, since he was the last one in. tag, you're it either the tune isn't right or possibly cam timing is off, one or the other, if he was paid to do the mods, he is responsible for the bike running properly after, unless he told the owner, before had that it wasn't going to work for some reason or another, this is a small modification, bike should run fairly well, op doesn't think its right, go back and let the tech tell him what is wrong
Ok. The original post didn't say anything about the bike not running properly or of any tuning performed. It simply stated, paraphrased, "hey I had some cams installed and the cam timing might be off", and that is what my initial post was in response to.

With the additional information in subsequent posts, I agree that the guy who did the work should have ensured the bike was operating properly before returning it to the customer, and should be responsible now to make it right.

The only caveat would be if the customer furnished his own parts and any of those parts turn out to be defective and the cause of the problem(s), then the customer needs to share some of the responsibilty.
 
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Old 10-12-2011, 07:13 PM
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Originally Posted by 2black1s
Ok. The original post didn't say anything about the bike not running properly or of any tuning performed. It simply stated, paraphrased, "hey I had some cams installed and the cam timing might be off", and that is what my initial post was in response to.

With the additional information in subsequent posts, I agree that the guy who did the work should have ensured the bike was operating properly before returning it to the customer, and should be responsible now to make it right.

The only caveat would be if the customer furnished his own parts and any of those parts turn out to be defective and the cause of the problem(s), then the customer needs to share some of the responsibilty.
The Harley shop provided the cams and the Power Vision was ordered from FuelMoto through the Harley shop. I was trying to diagnose things first because the service manager there is saying that it's definitely a problem with the tune and wants me to put a screaming eagle race tuner on it and have it dyno tuned at their location.
 


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