Low compression

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Aug 17, 2012 | 01:20 PM

#11

75hdxlh1000

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From: new england

ok will do.....thank you!

Aug 17, 2012 | 01:27 PM

#12

XL50#674

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From: Streetsboro, Oh

If i were you I would not reuse the pistons, i would pull the jugs, have them checked and go with a .30th overbore just to be safe and pick up a bit extra power while your at it.

Aug 18, 2012 | 09:44 PM

#13

75hdxlh1000

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From: new england

Quote:

Originally Posted by XL50#674

If i were you I would not reuse the pistons, i would pull the jugs, have them checked and go with a .30th overbore just to be safe and pick up a bit extra power while your at it.

Ok I got the heads off today and took a pic... I am going to change the pistons and rings...would .030" be the ideal overbore?

Last edited by 75hdxlh1000; Aug 18, 2012 at 09:55 PM. Reason: pic added

Aug 19, 2012 | 10:10 AM

#14

mrfikser

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From: Maryland near DC

I am looking at the pistons and rings and they look fine to me (from what I can tell from the pic)...how does the front head look???, any signs of a burnt valve???

Aug 19, 2012 | 05:21 PM

#15

75hdxlh1000

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From: new england

Quote:

Originally Posted by mrfikser

I am looking at the pistons and rings and they look fine to me (from what I can tell from the pic)...how does the front head look???, any signs of a burnt valve???

well the valves looked good but I noticed one of the rocker arms was sticking in the head assembly. I tried to pull one of the rings off and it broke in half!

Last edited by 75hdxlh1000; Aug 19, 2012 at 05:23 PM.

Aug 20, 2012 | 11:10 AM

#16

mrfikser

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From: Maryland near DC

yea, the rings are easy to break thats for sure...I would say the problem is in the head (the bikes, not yours)...If I were you I would go ask at the classic forum...they probably have more info on your bike..

Jun 18, 2017 | 10:18 AM

#17

kylecbruno92@gmail.com

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Joined: Jun 2017

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From: Rutland vt

75 iron head

Hey guys I have a 75 iron head and I'm having similar issues with my compression my front cylinder is pushing 105 psi while my rear is only pushing 35 psi. Plugs are dry what am I looking at needing to do to fix this issue

Jun 19, 2017 | 09:50 AM

#18

mrfikser

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From: Maryland near DC

do you realize that this posting is like ancient??...that said...I would start a new thread in the classics section, I am sure you will get a good bunch of replies....there is a series of tests you can do to help you get closer to the exact problem if not pinpoint it...low compression in just one cylinder is usually (if you are sure you did the rest right) a burnt valve, a wiped cam or some other part of the valve train being messed up or a cylinder ring issue..I would put my money on a valve issue and not a ring problem because it is only in one cylinder and 'usually' when it comes to rings both cylinders pretty much wear out the same amount (but not always)...do a forum search for low compression...do the tests and pretty soon you will be back on the road...