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Proper way to test for compression?

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  #41  
Old 10-19-2011, 10:38 PM
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The Harley shop wants to bring it in and check the timing "to make me happy" but I think they're gonna try to charge me for the work as well...even though any screw-up is their fault. I'm thinking I'll just ask them to diagnose why the compression is so far off and fix it that way since it would be a warranty item for sure. They're still trying to blame the tuner for the way it's running....
 
  #42  
Old 10-21-2011, 08:53 AM
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If you walked in there off the street and said bike wasnt running right or I did this cam job and something isnt right the first thing they would tell u is that the compression is way too low in one of the cylinders and say it must be fixed. since they are the ones that screwed it up they aren't going to admit it.
I have seen posts in here where the dots on the cams have been wrong right from factory, they are always a bitch to figure out when it happens.
 

Last edited by 2009blackpearle; 10-21-2011 at 08:56 AM.
  #43  
Old 10-21-2011, 02:51 PM
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Man, what a can of worms. First, I doubt if this involves the same malady that Sickbagger was cursed with, as I believe that bad batch of cams was manufactured in 2007 and mercifully should be out of circulation by now. If the OP bought them new it would surprise me if they are among the bad batch, although the dealer could've used old stock that had been sitting on the shelf for four years. This could happen, but if that was the case I think the OP would see no compression in one cylinder like SB observed during his little exercise in diagnostics. BTW, he is still the Diagnostic King (caps intended) in my book for that piece of detective work. Anyway, an examination of the cams will tell if the alignment dots are marked wrong, affecting the rear camshaft only. Attached is a photo showing the correct dot placement.

The reading of 190 sounds about right for a 96" motor with 255 cams (I would expect 185), a bit higher for a 103, but the lower reading in the other cylinder is neither normal nor acceptable. Since they told him a 25# variance is "normal," which it isn't, I wouldn't trust them to tell him the truth from here on out. Further, I would insist on watching them do the compression test and look at the gauge as it comes off the head.

As for the tuner, I don't think this is the problem, as my bike with 255 cams runs well with no stumbling or hard-starting using almost any tune, even stock. To clarify a bit, the PV will not run in closed-loop with WB sensors installed, but it doesn't need to. I'm running open-loop at all times and am using AT only for tuning. If this is the case with the OP, make sure Limits and Switches > Closed Loop is set to "0", which means closed-loop is disabled. That said, I'd bet a six-pack that the tune is not part of this problem.

Next, the OP's suggestion to buy SEPST is pure BS. (Warning: Acronym overload.) The PV does the same thing in that it is a flash-based tuner, and if the FM tune provided is the correct one it should run smooth enough without the aforementioned issues--the same even if it isn't the right tune. AFR's or timing would have to be way off to cause this behavior, based on my experience with my bike, and that isn't likely.

I think the OP should take the bike back to the dealer and watch them complete a compression test. If they get the same result and contend that it is "normal" I would take it to an indy and have him troubleshoot the issue, even though that will cost more money that will almost certainly not be refunded by the dealer, even if problems are found.

Another possibility that comes to mind would be sumping. If o-rings weren't installed properly during re-assembly scavenging may be affected, causing oil to accumulate in the crankcase. This can cause poor performance and excessive heat, but I haven't heard anyone with this problem to complain about hard starting or stumbling. To check, drain the oil from under the crankcase (not the pan) and measure. More than 6-8 oz. would be considered excessive.

Also, getting the cams off a tooth isn't as rare as it should be, and I suspect that a seasoned tech might have a tendency to do this more than someone like me who does it once every year or two and goes about it very slowly and carefully. After a tech does it twice a week for a few months he develops confidence, and I can see him moving along at a good clip, thinking he has his stuff in order. OTOH I would double- and triple-check the alignment both before and after the cam plate is reinstalled.
 
Attached Thumbnails Proper way to test for compression?-harley-cam-alignment-dot.jpg  

Last edited by iclick; 10-21-2011 at 03:21 PM.
  #44  
Old 10-21-2011, 05:41 PM
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I click can u read my post entitled ; what is it ; u follow all these things in here pretty close see if you have any ideas. I think i saw a post u had written on throttle plate sensor change. cost of part?
I dont want to jump this guys post with my problem i did reply earlier on my compression readings i took when i did my 255 103 kit last year 197-195 then did 10.5:1 pistons mva heads the next winter push compression up to 212 each cyl.
 

Last edited by 2009blackpearle; 10-21-2011 at 05:45 PM.
  #45  
Old 10-22-2011, 11:39 PM
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Originally Posted by 2009blackpearle
I click can u read my post entitled ; what is it ; ....
I'll take a look at that thread.
 

Last edited by iclick; 10-23-2011 at 12:19 AM.
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