Okay, so the engine guy on our FSAE team botched a rebuild of our '99 R6 engine. Now, the engine is extremely reluctant to turn (but not seized). It is so bad that it needs to be broken loose at the crank (we made a custom fitting for a ratched to grab) before the starter can turn it. We pulled the head so it is nothing in the valvetrain, nor is it the clutch or transmission. It takes about 90 foot-lbs to break it loose initially (after it's been sitting), and 40-50 foot lbs to turn the crank after that.

I've never done a rebuild but we're ready to write the motor off for the time being because of time (and because I don't trust that clown to rebuild it again) so I was going to mess with it, having nothing better to do over break. I know there are a lot of things it could be, like an incorrectly sized piston (one was replaced) etc. etc. But are there any suggested starting points to try?

--Angry Joe, who suddenly has a lot of time on his hands and the urge to mess with something, a dangerus combination

 

If you're convinced it's in the bottom end, I'd probably pull it apart and check the bearing clearances/torque of the rod and main cap bolts, and that he used the right caps for the correct position. the first rod I had off, I'd check to see how easy the piston was able to be cycled.

The first engine (car) I rebuilt was an old 289. I didn't put the main caps back on in the way they came off, thing was a BEE-ATCH to turn. Ended up scraping the crud out of the bearings. Had to replace the bearings and put things back in the correct position. Worked like a charm.

I mean, did he bore it out any? Why would he have changed piston sizes?

Other than that, all I can think of at this point is the rings are incorrect or the bearings incorrect But then again, I've only done one sport bike rebuild, so I'm far from a master, that's just what comes to the top of my mind right now.

 

Red flags in your situation are rings and bearings. I'd check ring direction (face up on piston), piston direction (mark to front of engine), ring order(top/2nd/oil control) although I don't see how a human being can mess that up but who knows. If that shows no go I'd take out the piston/rods one at a time and try turning the crank after each comes out. If it suddenly gets better, you know which piston it is. If it's still bad then you're looking at main bearings. Buy a set and plasticgage them like a good boy and you should be set. Make sure to torque everything down in sequence and gradually in say 3 rounds. aka if the final torque is 85lb/ft go around the tightening sequence at say 40lb/ft, then 65lb/ft until finally the 85 spec. Hope that helps

 

Check the starter drive gears and cam cap torque as well. Basically check all rotating assemblies...if something has shims on it (transmission shafts) check it twice as a misplaced shim can jam things up and be really difficult to diagnose.

If you don't have a factory Yamaha service manual, this would be your cue to get ahold of one, btw....Haynes/Chilton don't usually cut it in the bike world IMHO.

 

Problem is definitely not with cams or anything in the head or transmission but we'll check. We just pulled the head and the pistons are in correctly so it's not that. And yes, we have a factory manual

Thanks for the suggestions guys. The bottom end is next...

 

most likely improper clearances in either main bearings, rod bearings, rod side clearance or crank thrust washers. Or maybe if you're lucky (depending how you look at it) he just torqued stuff together incorrectly. IE: he didn't bolt in the main caps/bridge in order or in steps. I've seen at least one guy torque down a main crank bridge to final spec starting at one end to the other. Needless to say the crank wouldn't rotate cleanly and only w/ a 4' breaker bar. Good luck guys

 

We pulled the end cap of the first piston, I'm not sure this looks right (sorry it came out kinda crappy) I took pictures of other surfaces but they came out like crap. They all look good to me though. We're going back to the lab to check the other three pistons now, but for sure the #1 piston itself is not the problem.




[Modified by Angry Joe, 9:13 PM 12/20/2002]

 

I think we've found the problem. One of the big connecting rod bearings is majorly fucked! There's heat scarring and one side of it is chewed up, when we pulled it off (which was a bitch) a small piece of it fell off! I'll post pics when I get home. Oh, and effort to turn the engine dropped from 35 ft-lbs to 10-15 ft-lbs. Any thoughts on the cause? Overtorquing perhaps?

 

*shrug* myriad reasons. Crappy bearing, improper clearance, debris in your assembly lube, bearing spun slightly when he put it on, tweaked con rod, cap not installed in the correct position or direction, over torque. There's probably more.

When you reassemble it, try plastigauging the whole thing before you do lube & final assembly. Double check your clearances.

edit: btw, congrats on finding it.


[Modified by project_mercy, 6:07 AM 12/21/2002]

 

So, does this look bad to you? The debris near the bottom of the photo is a piece of the bearing

 

That's pretty bad but I've seen worse. I would bet improper bearing crush was the beginning of the problem. The cause is much harder to determine... have fun