external headgasket leak on evo???? : V-Twin Forum: Harley Davidson Forums

bronco71 · 07-28-2008, 09:47 PM

A friend of mine stopped buy tonight and had a chirp noise in his bike when it was cold. After a couple of hours we started the bike up cold and sure enough it chirped on the right side. I felt my fingers around the carb thinking maybe an intake or exhaust gasket. Then there it was air pushing out of the motor which felt like the head gsket on the rear cylinder head. I have had twin cams apart but never an Evo. First off is it possible to have an external leak on either motor? Second motor work has been done to the bike but he is not sure what, so what would cause this? When I take this apart is there something special I should look at?

springer- · 07-28-2008, 10:43 PM

A head gasket leak can usually be felt on the outside of the engine where the head meets the cylinder. There are several possible causes. Excessive compression blowing out a portion of the gasket, least likely. Loss of clamp load of the head bolt(s). Clamp load loss could be from improper torque, pulled case threads or using Stainless Steel head bolts.

After taking it apart examine the head gasket surface on both the cylinder and head for burned in grooves. You would be surprised how bad a head gasket leak can burn away metal.

Lakerat · 07-29-2008, 09:51 AM

When my 92 FXR blew out the head gasket, I was told the most likely cause was improper warm up before riding. Since then, my petcock is left off on initial start up and let it idle until the fuel in the carburetor is gone. Then I turn the fuel back on and restart, still taking it easy until the rocker box is up to temp.

bronco71 · 07-29-2008, 04:13 PM

Further diagnosis I did find the base gaskets leaking oil. There also is an oil leak at both head gaskets. I listened with a stethoscope and definitely found the noise at the rear head gasket and it appears to look like a gap there. Hopefully I will get a chance this week to take it apart. Was it common to big bore an evo or just put a cam in them?

1997bagger · 07-29-2008, 07:25 PM

Big boring an Evo requires the spigot holes to be opened up, which is case splitting. Bore the cylinders to clean them up and bump the comp ratio up (head milling or piston height), choose a cam for the riding style.
James base gaskets and check the sealing area of the jug base closely.
Many different combinations out there, some work, some don't, do your homework.

Hillside · 07-30-2008, 05:37 AM

Head gaskets come apart on occasion. Not the end of the world.
Pull it down, and look to see if the studs are not pulled as mentioned.
May be able to just re-hone, re-ring, with Cometic gaskets, and back in the saddle.
If "more" is what you may be interested in, then a good multi-angle valve job, head re-surface,(along with the re-ring) and either a Bob Wood W-6 cam, or an Andrews EV-27 (a little less power) and it will roll 75-80 hp and 85-90 ft/lbs, with a good pipe(s), and tuned. Increased fuel economy as well.

bronco71 · 08-04-2008, 09:30 PM

Finally took my buddies bike apart. Didn't really see anything except carbon on jug side of gasket. Checked flatness of head and top of cylinder both under .002. I believe Harley spec was .006. I did not re-ring it because he was selling it and has low miles on the bike. The guy he bought the bike from had motor work done to it. It looked like it had high compression pistons, some head work done, and I now it had a cam in it. It also had a s&s super e shorty. When I started it it did not idle right. I re-adjusted the carb and road tested where it sputtered. The rear head plug wire was arching at the coil. All seemed OK after that was fixed. I did not ride the bike before my repair but noticed when tunning the carb that white smoke was coming from the back head when I blurped the throttle. Does this sound like valve guide seals or rings? He wants to sell it and buy a street glide what do people think a 93 evo softail with all the fix-ins is worth?

springer- · 08-04-2008, 10:08 PM

Quote:

Originally Posted by bronco71

.... what do people think a 93 evo softail with all the fix-ins is worth?

That's a tough call. Not knowing anything about it or being able to look it over??? It is worth whatever you can get someone to pay. IMO, the '93 engine had a few faults, mainly thing spigot wall at the rear lifter block area.

I passed on a '98 softail for 9K, a '93 sight unseen and with the mods and problems you listed I would pass at 7K, JMO.