Bad News

[reddirtrider]

Did you check the rod bearing clearances during the rebuild?

That really sucks. Check around, it may not cost as much as you think to get it running again. You can reuse may of the same parts. One rod bearing and worst case a crank. Add to that a head gasket and you should be good to go.

[bwringer]

Dang, Dave, so sorry to hear this. It's such a nice bike, and it was good to meet you when you stopped by last night when you were in Indy. It seemed to be running so nicely when you left, too.

Something else was wrong to cause two failures in a row like that. I hope maybe you can find another 650G engine or even just the bottom end cheap. They do pop up.

Now if you needed an 850G bottom end, we could do some business...

[Dave_17954]

actually this was the only failure like that. The original problem was just the fact the #4 bearing was worn quite a bit and the #3 bearing a little bit plus the ring marks from sitting to long in the #4 cylinder. Yes i measured everything when i had it down and everything was well within the original specs for standard bearing replacements which is what i ordered. guess i'll tear it down just to satisfy my curiosity. At least i know the bolts wont be to hard to get out and i wont have to clean anything up in side the motor.....

[Nessism]

Bummer about the crank. There must have been some sort of oiling system obstruction. Did you pull the pump apart during the rebuild?

[Dave_17954]

i cleaned that motor so good on the inside you could have ate your lunch off of it. and yes i did take apart the oil pump also installed all new seals....i'm gonna tear it all back apart. will post pix. maybe i'll find that 10mm socket that seemed to come up missing just hurts to laugh anymore . i'm tired

[chef1366]

I bet you can find a crank.

[jimcor]

Man, I know how you feel. I rebuilt a little BSA engine and less than 50 miles later it was trash. All my fault, brute force engineering doesn't work.

Good luck with the bike and the job situation.

[Don-lo]

OMG, this bums me out. PM sent.

[reddirtrider]

actually this was the only failure like that. The original problem was just the fact the #4 bearing was worn quite a bit and the #3 bearing a little bit plus the ring marks from sitting to long in the #4 cylinder. Yes i measured everything when i had it down and everything was well within the original specs for standard bearing replacements which is what i ordered. guess i'll tear it down just to satisfy my curiosity. At least i know the bolts wont be to hard to get out and i wont have to clean anything up in side the motor.....

I've never replaced bearings on a bike motor before, but I've built lots of car engines. What I used to measure the bearing clearances, while they were installed and torgued down is plastiguage. I didn't take for granted that the bearings I bought were all correct. That's what I was refering to when I asked if you measured the bearing clearances.

I don't understand how this could happen to a motor that was cleaned and prepared as thoroughly as yours. There had to be a problem with that bearing, or the oil delivery to it.

The alternative to plastigauge is to mike the crank throw, then the inside bearing surface on the rod with the cap torqued down, and then subtract the difference. Is that what you did?

[errorcauser]

Reading this bums me out as well. If there was anyway I could help I would.

But, I'm one of those people that has a heart as big as Texas, as the ole saying goes. I try to help everyone that I can.

[Dave_17954]

I'm assuming the nuts have worked loose somehow. I havent got it torn down that far yet tho. The piston still moves up and down so that tells me the rod hasnt broken in 2 pieces and that the nuts are still on the rod bolts. I can run the piston to tdc then roll it past just a smidge then push down on the piston with my dowell rod and it will drop I'd guess a good 3/16 or so. Even if there was an oiling problem which I dont think there is I dont see how that could affect the nuts. Like i said i double checked my torque when i put them on plus red loctited them to boot. basically wondering since i done them all the same way why is this one the only one that came loose. I ran this engine for about 700 miles before this happend and changed oil in it twice. It always ran as quiet as a mouse except for a little shim noise. I set my clearances at .07 -.09 figuring they would close up a bit once my valves got reseated good. I did use plastic gauge on my bearing clearances to btw. Ive rebuilt many an air cooled engine in the last 10 yrs actually I used to do this as my regular job before i became a machinist even went to school for it. As soon as I get it opened up I'll be posting pix. Something happens to my suzi i take it personally. The top pic is of the # 3 rod cap and nuts during the rebuild and the lower 2 are the rod and bearing during the original motor teardown.

[TheCafeKid]

Sorry to hear this Dave She's a looker. And, sadly, yet another plain bearing, high pressure mill bites the dust. I replaced the motor in an 83 550ES that suffered the same fate. Same cylinder as a matter of fact. Found it was far quicker and cheaper to simply hunt up another motor instead of tearing it all apart and replacing everything, sending the crank off, etc etc... The 550s were a bit more pleantiful than the 650s perhaps, so maybe in your case it will be your only option. That really sucks dude If i can help any, let me know...



Josh

[Bribird]

Dude!That sucks! That is just too weird for real!! I had the exact same thing happen to my bike after the first build.. Some how the con rod nuts backed off on the #4 cylinder.. I was sure I torqued everything right. When i tore the motor back down, all it needing was some new con rod bearings on the #4 and everything else checked out fine. If you end up needing a crank... let me know.. I will get one to you.

I truly feel your pain Dave, you know, come to think of it, I would suspect your helper.

[Dave_17954]

Heres a pic of the new style conrod bearings on the left and the new style crank bearings on the right. thanks josh. you putting them service manuals to good use? lol
when your laid off you got a lot of time so i figured I might as well tear it apart curiosity will kill me if I dont do it . I know it will be easier than the first time around and cleaner to . I remember you telling me that brian and that was before i had put mine back together so I was very conscious of the fact to double check them. I can sense some green loctite this time around. I'm hoping it will just be a ruined bearing like yours. I'm going over it with an even finer comb this time. And on a lighter note at least I'll no which way to stick that crank seal in this time......lol. I think shes jealous brian lol.

[Dave_17954]

preliminary news

Well so far I've found no damage at all to the valve area. Shims, buckets, cams, cam bearings all look good. Valve area itself looks very good. Found no loose bolts or nuts on the top end anywhere. The cylinder looks great no scoring on the walls in any of the cylinders. You can still see the hone marks in all 4. the pistons all look good so far. no broken rings or any sign of damage on the skirts. Numbers 1,2,4 rods are all tight and #3 is severely loose. Just glancing down inside the case at #3 I can see no sign of metal fragments anywhere but this very preliminary. I'll post up some pix later tonight. Tomorrow if I get a chance I'll pull the lower end out of the frame and split open.