Setting Idle
I do not recall seeing compression test numbers anywhere in the factory service manuals. Must be there somewhere as other guys refer to them from time to time. Anyway, "they say" that 120 is at the low end of normal. A recently rebuilt engine will show 160 to 180. 120 is OK, but the engine will need a top end in its near furture.
I would just keep this in mind and tend to all of the other things, and re-visit this in another year or so when everything else is straightened away. There are usually lots of "little bad things" left behind by POs.
I would just keep this in mind and tend to all of the other things, and re-visit this in another year or so when everything else is straightened away. There are usually lots of "little bad things" left behind by POs.
Thread Starter
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Cruiser
Joined: Oct 2010
Posts: 165
Likes: 0
From: Houston Texas
Top End
being that the bike has only about 18,000 miles, and am not starting a new thread here, this is for future planning.
will it be only the heads? or can it be a little deeper like rings also. I think that back in 81 the EPA was all over everyones but,
so i think without looking things up that i have a factory 9.0 compression, or close to it, so 120 on the dot, and i know the importance
of the 120 figures being equal is not bad i think, but that is a job for when i can have the heads ported.
am wondering, and having a car engine background i would answer me this way.
we have to check cylinder bore DIM to see how much wear is there. what is all that is involved in a head job,
1- pull it out
2- check guides
3- seat the valves
5- resurface head to cylinder.
Then is it better to get a cylinder kit or bore my cylinder and put rings and pistons.
By the way i went back to Harley Dealer today, found a guy there that i never seen before, he claimed that he
used to work for a local guy that had a shop here and ended up closing it down, but he relocated the machine shop
part to another location in Baytown Texas, its about 25 miles away one way, ( dont know how much you guys know
about Texas but 25 miles is like going to the corner store ) anyhow he claims they stil have an Ironhead that runs
nitro and they run it 1/8 mile, he told me about how one visitor one time was near the carb when they were starting it
and it did a carb burp fire and scared the crap out of the guy. long BS Story short i have the number and am going to call
the guy, never know, am told he can do anything in his machine shop.
The bike runs very good and strong now so its out of the question, But almost any vehicle i have really cared for has had PORTED HEADS, the difference in performance is so great i have never pass it up.
will it be only the heads? or can it be a little deeper like rings also. I think that back in 81 the EPA was all over everyones but,
so i think without looking things up that i have a factory 9.0 compression, or close to it, so 120 on the dot, and i know the importance
of the 120 figures being equal is not bad i think, but that is a job for when i can have the heads ported.
am wondering, and having a car engine background i would answer me this way.
we have to check cylinder bore DIM to see how much wear is there. what is all that is involved in a head job,
1- pull it out
2- check guides
3- seat the valves
5- resurface head to cylinder.
Then is it better to get a cylinder kit or bore my cylinder and put rings and pistons.
By the way i went back to Harley Dealer today, found a guy there that i never seen before, he claimed that he
used to work for a local guy that had a shop here and ended up closing it down, but he relocated the machine shop
part to another location in Baytown Texas, its about 25 miles away one way, ( dont know how much you guys know
about Texas but 25 miles is like going to the corner store ) anyhow he claims they stil have an Ironhead that runs
nitro and they run it 1/8 mile, he told me about how one visitor one time was near the carb when they were starting it
and it did a carb burp fire and scared the crap out of the guy. long BS Story short i have the number and am going to call
the guy, never know, am told he can do anything in his machine shop.
The bike runs very good and strong now so its out of the question, But almost any vehicle i have really cared for has had PORTED HEADS, the difference in performance is so great i have never pass it up.
Last edited by Neal Perez; Feb 7, 2011 at 11:25 PM.
Tourer
Joined: Apr 2010
Posts: 293
Likes: 7
The reading on the compression gauge can reveal a problem, but is not necessarily any indication of engine health at all.
The reading is a combination of sealing integrity(whether or not there has been a "failure"), normal engine wear, speed of engine at test(kick, high gear electric, etc), and most importantly, camshaft fitted. Other factors, like gauge quality, can have an impact, but are not really part of the equation, so typically are assumed to have no effect.
This is why the emphasis is always on the 2 cyls being close to the same, as opposed to the actual reason.
A variation here is often more telling than the actual number achieved (depending of which dynamic you are addressing, of course).
Are you using oil?
Are you blowing smoke?
If no, what are you trying to achieve?
The reading is a combination of sealing integrity(whether or not there has been a "failure"), normal engine wear, speed of engine at test(kick, high gear electric, etc), and most importantly, camshaft fitted. Other factors, like gauge quality, can have an impact, but are not really part of the equation, so typically are assumed to have no effect.
This is why the emphasis is always on the 2 cyls being close to the same, as opposed to the actual reason.
A variation here is often more telling than the actual number achieved (depending of which dynamic you are addressing, of course).
Are you using oil?
Are you blowing smoke?
If no, what are you trying to achieve?
Road Captain
Joined: Oct 2010
Posts: 566
Likes: 3
From: rural ontario
I check the compression on mine frequently, It is a quick and easy way to tell if it is time to adjust the pushrods. Aside from that...if you're not burning oil or leaking oil...and your compression sounds ok (as it does) then don't entertain the idea of fixing it until it needs it. Ride it!!
Road Captain
Joined: Oct 2010
Posts: 566
Likes: 3
From: rural ontario
If you come up to Michigan and cut through southern Ontario on your way to Maine you should stop in for a beer on your way...I'm not toooo far off the highway and I've always got beer in the fridge. In three months...riding season should be in full swing by then...yup, we could go for a ride! 
Thread Starter
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Cruiser
Joined: Oct 2010
Posts: 165
Likes: 0
From: Houston Texas
Thank you sir, am sure we would have a great time doing some riding, one day when the lady and i can take a trip with a little time there is a posibility.
My niece is having twins, and i have to go up there and help unless i can get someone else to go, i know that side of the continent is beautiful that time of the year, for us here in Houston we have the low lands, you have to go nothwest to see some wooded landscape and nicer scenery.
My niece is having twins, and i have to go up there and help unless i can get someone else to go, i know that side of the continent is beautiful that time of the year, for us here in Houston we have the low lands, you have to go nothwest to see some wooded landscape and nicer scenery.
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