Wednesday, July 8, 2009

Pop Quiz

I started up my ’84 Ironhead the other day and it ran like crap. Rather than try and guess what the problem was, I decided to practice what I preach. I did a compression test and these are the results:
Front cylinder dry 125 psi
Front cylinder wet 125 psi
Rear cylinder dry 170 psi
Rear cylinder wet 170 psi
So, what is the logical place to look for the problem?

14 comments:

Ann said...

Umm, the motor?

No charge for that, BTW. :)

Danny said...

Depends on what the compression is supposed to be. I will GUESS the front cylinder is where to look first.

Arizona Harley Dude said...

Check to see if the plug is tight in the front head and then the head pipe. Just guessing here, as I really don't have a clue.

Mastercheif said...

How's your fuel. Has it been sitting for a while. Maybe moisture problem? Swap out plugs? Go hump a marshmellow?

fasthair said...

Since you didn't say how crappy it ran I'll just guess it was missing and maybe back firing through the carb or out the exhaust? Since the compression didn't change from dry and wet then I can safely ASSume that the rings/cylinders are not the problem. Time for a cylinder leak test. While 125psi is low it should still be able to fire that cylinder. But then again running compression will be lower so maybe not. I vote for valve problems. Being an iron head I'm guessing exhaust valve issues. What did I win?

fasthair

BlackstoneBill said...

Check your left front pocket. If there isn't a mouse in it it may have built a nest in the exhaust pipe for you rear cyl.

When you figure out your problem and get it fixed are we going to see a Final Battle VI?

Big Daddy said...

Fasthair has you on the right track.
Check the valves
Adjust the pushrods until the are tight but can still be turned by hand.
[no up and down movement...but able to spin it with your fingers]
usually in a ironhead this is the problem.


All this is assuming no one replaced the pushrod tubes with camuflage ones....in that case just sell the damn thing, Cos you ain't ever gonna find them..;]

FLHX_Dave said...

Oh hell...this is freakin' easy! You dumb assholes have no idea wtf you are talking about.

Look, it's not the rings or the bore. If that was the case then the wet compression test would have been slightly higher than dry compression test.

It's the intake valve bro. Plain and simple.

geez...Here is the real quiz. How the hell did I know this?

mq01 said...

sitting back and listening and learning, im listening... so...are they camo pushrods ;)

Mr. Motorcycle said...

Seeing as I've never wrenched on a Harley motor, I'm gonna go with Ann's answer. I like that one best.

Webster World said...

Old nasty ass gas>

FLHX_Dave said...

I wasn't serious. C'mon!

Willy D said...

Ann: I’m sending you a bill for a new motor

Danny: You’re on the right cylinder.

AHD: Plugs! I knew I forgot something!

Mastercheif: The fuel came with the bike, it worked fine then. We’ll leave the marshmallow humping for your brother.

fasthair: I already knew what the issue was, this was just a quiz. I ran the valves and now have 185 psi on both cylinders. The low compression on the front was the intake valve.
What’d you win? How about a free oil change and tire rotation at you local Mercedes shop.

Bill: I checked my pocket; all’s I found was a couple of rubber balls. I’m working on more of the story. Coming soon to a blog near you.

Big D: Valve adjustment is always a issue on these old-fart bikes. I also developed a high RPM miss that I’ll post pics of the cause soon. Damn weights! The camouflaged pushrod is probably behind your camouflaged zipper ;)

Dave: Damn! You one smart dude! After I told you what was wrong with it.

mq01: Don’t know. Can’t find the things.

Mr. M: Good. I’ll send you half the bill.

Webster: Gas is good. Might be the marshmallows I put in it.

fasthair said...

damn I missed it by --- that much! I forgot those old engines had adjustable pushrods. Free oil change? Are you kidding? Not from my cheap ass boss!

fasthair