Top end rebuild Question

[Mike Hufnagel]

Usually I'm really careful on rebuilding top ends, but some dirt got into the bottom end when I pulled off the cylinder.My old drag bike, TZ350) would flood like crazy when I was first setting it up and a few oz. of gas would be in the bottom and I would have no problems. So i would assume dumping some gas or solvent into the bottom end and rinsing it out, then putting lightly oiling it would have no adverse affect.  Any one disagree?

[thrownchain]

I disagree, you can "rinse" out the bottom end, but you most likely won't get out all the dirt. Only way to know for sure is a total dis-assenbly and clean it, then re-assemble with clean parts. You might get away with the rinse, but............

[joe novak]

Hello,  I am glad you asked that question.  I washed out the bottom end of a friend's RM Suzuki that was literally filled with mud and water.   He sunk it in an Ohio mud hole.  I used warm, soapy water and repeatedly wrinsed the bottom end while working the crank until it rotated smoothly.   The cylinder was bored, and a new piston installed.   The bike ran forever under racing conditions with no bottom end failure!   I do not recommend using solvent for wrinsing out the bottom end.  They do not easily break down dirt (if you mean "soil").  You most certainly want to lubricate the bottom end bearings and the rod bearing before assembly.  Maybe we were just lucky this time?  How big was that chunk of dirt which fell in your crankcase?

[Mike Hufnagel]

It wasn't a chunk or nothing that big. Just some "grit" ,so to speak, got in there when I pulled the cylinder off.

[joe novak]

Just remember to stuff the crank area with rags  before you remove the wrist pin clips.   I have heard of those dropping down there...  or worse, yet, the clip was lost, and found later in the crankcase.

[Mike Hufnagel]

or even worse, buttoning it all back up and noticing a left over circlip.

[400gs6]

quote:Originally posted by Mike Hufnagel

or even worse, buttoning it all back up and noticing a left over circlip.

...[:I]  I hear ya.  Years ago as a kid wrenching at aHonda delership, I replaced some trans gears on a CB 360 Honda.  Got the cases all together, cylinder in place, head bolted up with cam chain and all.  Bolted the motor into the frame, cables and the last item was the countershaft sprocket.  Did you know the countershaft can be installed backwards on those old Hondas!  Arrrgghhhh!

[Big Mac]

I'd attach a 1/4" piece of tubing to an air chuck in the air compressor hose, then feed it down around the crank webs on one side and blow the heck out of it. Likely it will blow the debris up out the other side. Not a lot for it to get caught up on, smooth sides inside the lower end.

After that, I'd spray in a big dose of WD40, slosh around and take out the drain screw from the bottom between the fins, and see what washes out. Then I'd feed a clean rag in one side and turn the crank over to pull it up out the other side, to wipe out anything that might still be in there.

If the crank turns around smooth and quiet with no obvious grit in the bearings, any debris that otherwise survives can't do too much harm and should blow by and out the first time it fires up. These motors are tougher than people give them credit for.

I ran a rebuilt 495 motor for a dozen motos, had the clutch cover off to check plates and noticed that a complete tooth was broken off and missing from the primary/pinion gear on the crank end. Nowhere to be found, nothing found on the clutch side. Drained all the oil out real good, rinsed the trans with gas, fished out some small bits and tiny chunks of gear tooth with a magnetic screwdriver tip through the oil drain hole. I replaced the gear, put a magnetized tip drain bolt back in and refilled, ran more races, no issues or noises. When I checked the drain plug afterward, a few more shavings and some tiny shiny bits came out. No apparent problems.

[Rain Man]

And the moral of the story is "clean all the nooks and cranies of the engine with a toothbrush and scratch awl" before ever taken anything apart.

Raymond
 Down East Pentons