Compression???????
Thread Starter
|
Cruiser
Joined: Feb 2007
Posts: 138
Likes: 5
From: Dublin, Ireland.
Compression???????
As stated in earlier threads, I have done a top-end rebuild to cure a leaky base gasket. Honed cylinders, new rings, valve re-grind plus all gaskets. Also fitted an EV27 cam, (which I am delighted with).
Now after about 100 miles or so, on idle it smokes a little bit so I decided to do a compression test.
My Clymer manual says 90 psi is normal, I am getting a reading of 165 psi, both cylinders within a lb or two of each other, so, of course, I am chuffed.
But if 90 is normal why am I so much higher?
The engine is standard with standard size pistons, no re-bore or anything like that. As I said, only the EV27, an S&S super E and Scremin eagle ignition coil module.
Does the cam make a difference?
Thanks.
Tony.
Now after about 100 miles or so, on idle it smokes a little bit so I decided to do a compression test.
My Clymer manual says 90 psi is normal, I am getting a reading of 165 psi, both cylinders within a lb or two of each other, so, of course, I am chuffed.
But if 90 is normal why am I so much higher?
The engine is standard with standard size pistons, no re-bore or anything like that. As I said, only the EV27, an S&S super E and Scremin eagle ignition coil module.
Does the cam make a difference?
Thanks.
Tony.
Seasoned HDF Member
Joined: Aug 2007
Posts: 8,198
Likes: 3,087
From: NW AR
I wouldn't be concerned about it. The more import measurement is the no difference between cylinders. 90 might be borderline acceptable, that is, if it's 90 you can get by without a rebuild. 160 is more "normal" for a typical motor, not necessarily a HD. And, as SG states, everyone's gauge is different to some extent or other. Mine, for example, just presses a rubber stopper against the spark plug hole. My other compression gauge, the one I always carry with me, is my thumb, and calibration on that one is not too close, but it's always "handy." It has more of a binary calibration: Has compression, doesn't have compression.
A cam will make a difference in the compression reading. A big cam can give you lower readings on the gauge from valve overlap.
A cam will make a difference in the compression reading. A big cam can give you lower readings on the gauge from valve overlap.
Thread Starter
|
Cruiser
Joined: Feb 2007
Posts: 138
Likes: 5
From: Dublin, Ireland.
Thanks for replies.
Should have said tried two different gauges. One was screw in type, (like a plug) that gave 165 repeatedly. The other was a push and hold on type, (no, not thumb!!!) that gave a slightly lower reading, 155 lbs which I put down to the fact that it is hard to hold on.
As Dr.Hess said, as both are more or less same I will not worry.
Tony.
Should have said tried two different gauges. One was screw in type, (like a plug) that gave 165 repeatedly. The other was a push and hold on type, (no, not thumb!!!) that gave a slightly lower reading, 155 lbs which I put down to the fact that it is hard to hold on.
As Dr.Hess said, as both are more or less same I will not worry.
Tony.
Banned
Joined: Sep 2009
Posts: 7,580
Likes: 7
From: The Internet (& Dyer, Indiana)
A cam will make a difference in the compression reading. A big cam can give you lower readings on the gauge from valve overlap.
Early close = higher compression reading.
Yours seams normal.
Hopefully the rings will seat better with time. Shouldn't be smoking, unless you put one of the rings in upside down. Does it smoke both cylinders?
Seasoned HDF Member
Joined: Aug 2008
Posts: 5,078
Likes: 2,150
From: Ohio
EV27 is a compresson builder so your compression sounds normal, with the compression ok you wouldn't think you have oil getting past the rings. I believe you mentioned earlier that you installed a Super E with the rebuild, is it possible the idle circuit is alittle rich and the smoke you notice? if I'm wrong on the carb install, please disregard.
Banned
Joined: Sep 2009
Posts: 7,580
Likes: 7
From: The Internet (& Dyer, Indiana)
EV27 is a compresson builder so your compression sounds normal, with the compression ok you wouldn't think you have oil getting past the rings. I believe you mentioned earlier that you installed a Super E with the rebuild, is it possible the idle circuit is alittle rich and the smoke you notice? if I'm wrong on the carb install, please disregard.
Good point. He never did say what color the smoke was.
Trending Topics
Thread Starter
|
Cruiser
Joined: Feb 2007
Posts: 138
Likes: 5
From: Dublin, Ireland.
No, I always had Super E.
I suppose smoke would be a bluish color and is same from both cylinders.
Now it's not much, but noticeable only on idle. It goes when engine is revved and not there at all while running under load or on over-run, (de-cellerating).
Tony.
I suppose smoke would be a bluish color and is same from both cylinders.
Now it's not much, but noticeable only on idle. It goes when engine is revved and not there at all while running under load or on over-run, (de-cellerating).
Tony.
HD Forum Stories
The Best of Harley-Davidson for Lifelong Riders
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Verdad Gallardo
8 Best Harley-Davidson Motorcycles Ever
Pouria Savadkouei
10 Worst Harley-Davidson Motorcycles Ever
Pouria Savadkouei
Killer Custom's Jail Break Is The Breakout That Refused to Blend In
Verdad Gallardo
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Verdad Gallardo
Harley-Davidson Reveals Super Cool Cafe Racer Concept
Verdad Gallardo
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Verdad Gallardo
10 Motorcycles You Should Never Buy
Joe Kucinski
10 Things Harley-Davidson Needs to Fix in 2026
Verdad Gallardo
Road Warrior
Joined: Jan 2007
Posts: 1,276
Likes: 8
From: Minneapolis Area, MN
I had a smoke issue a few years ago on my EVO when I put in an EV27. After running a couple hundred miles I have some blue-ish smoke. It turned out to be valve guide seals. All I could come up with is that the EV27 had ever so slightly more lift which pushed a previously un-wiped / rougher portion of the valve stem into the seal causing it to damage the seal enough to allow oil through. I had to tear into it.
Ended up boring the cylinders .010", new rings, valve job, port, shaved heads, new springs...got her back together and it still smoked. This time it was the rings that didn't take. I did a compression test and it tested fine...never did a leakdown test at that time. I had to tear into it...again.
Honed cylinders, new rings, put together with dry (no oil) cylinders and haven't had a problem since.
Not sure that helps at all.
Ended up boring the cylinders .010", new rings, valve job, port, shaved heads, new springs...got her back together and it still smoked. This time it was the rings that didn't take. I did a compression test and it tested fine...never did a leakdown test at that time. I had to tear into it...again.
Honed cylinders, new rings, put together with dry (no oil) cylinders and haven't had a problem since.
Not sure that helps at all.
Thread
Thread Starter
Forum
Replies
Last Post
