My New Topend is Toast!!!

ericfreeman · #1 20th May 2008

Posted this in the Ironhead section but thought it might be interesting to see what advice I'd get from this group, perhaps some good points to prevent it from happening again.

Only 1500 miles on my new topend: worked over heads, new Wiseco 10:1 pistons, R5 cams, etc. Bike has been running fantastic, until last Thursday. Went for my usual 80 mile run on some backroads and wound up on a stretch of highway where I had to keep up with traffic at about 65 mph. No big deal right? Well, after coming back down to slower speed I noticed some pinging and other signs of not running perfectly. Made it home OK but noticed a definite knock/slap sound from the front cylinder. Did a compression test the next day and found the front cylinder down about 50 psi from the rear. Also wanted to check the timing but I'm not getting a consistent flash from the front coil (rear coil is firing fine). Not sure if this is related to the piston problem or not.

Pulled the front head (looks fine) and jug and found this.

The galling is on the intake side of the front piston. Scoring on the barrel is not deep but you can feel it, so a rebore is likely. Will have to pull the rear head and barrel as well to have them both done together.

Biggest disappointment is I've been taking great pains to ensure I never ran lean while breaking in the new top end. My big Weber carb is jetted pretty much as recommended by several other fellows running them and by the Weber jetting expert back east. Bike just never felt like it was running lean (needs a little enrichener when cold, never any carb farts) and judging by the exhaust pipe it appears to be a little too rich.

Anyway, will be sending the barrels off later in the week for inspection and I'll change jets on the carb to richen up the mixture. Pisses me off to have screwed up bad enough to wreck my new top end. Still need to look in to why the front cylinder spark seems erratic since it's a single fire setup with independent coils. Don't know if a bad coil (it's nearly new as well) could have contributed to overheating condition.

Guess I'll be riding my Honda Trail 90 for the time being!!

Eric
Sportsterless North of Seattle

Cannonball · #2 20th May 2008

Sorry you're having problems. However, I wouldn't make it any richer though. I recently pulled a motor apart that was too rich and saw what you are seeing. Just like too lean, too rich is bad news too. The reason being, in the motors early stages, lubrication of the cylinder is paramount. Your cross hatching in the cylinders is to retain oil to lube the rings as they travel up and down. When you run the motor too rich you create a wash out scenario, in which the excess raw fuel literally cleans the oil from the cylinder walls and the piston travels back up in a dry cylinder. By the looks of your piston it's looking like it's quite rich. May be something to look into. My 2 cents anyways.

ericfreeman · #3 20th May 2008

Good point about cylinder washdown. Now I don't know what the hell to do!! Run leaner or richer? Wish I could hook up an O2 sensor to see what's going on when running. Not practical though with my current setup. Thanks for the observation/advice.

Eric

blakjak · #4 20th May 2008

I'm not much on expertise but about the only good way I know for those of us with no EFI or O2 sensors is a dyno run to figure out the right AFR.

83XLX · #5 20th May 2008

Can't tell too well from the pics - is part of your oil ring missing, or is it even there?

ericfreeman · #6 20th May 2008

Quote:

Originally Posted by 83XLX

Can't tell too well from the pics - is part of your oil ring missing, or is it even there?

I had removed the rings before taking the picture of the piston. Rings looked fine.

Eric

Cannonball · #7 20th May 2008

Quote:

Originally Posted by ericfreeman

Good point about cylinder washdown. Now I don't know what the hell to do!! Run leaner or richer? Wish I could hook up an O2 sensor to see what's going on when running. Not practical though with my current setup. Thanks for the observation/advice.

Eric

Hey Eric,
You can hook up an O2 sensor if you want to put in a few hours of work. Weld on a bung, buy an aftermarket O2 sensor, and a guage. Here's some of Autometer's Guages. These can be retro-fit to anything.
http://shopping.yahoo.com/s:Individu...NsawNzc2VhcmNo