Topic: Opinions, please

[mystic_1]

So now that the weather is a bit more tolerable here in the Chicago area I have been spending more time sorting and inspecting my collection of part (ie my disassembled motorcycle ).

I need to replace my pistons.  I have a set out of a 73 motor, but they have some oxidation going on in the skirt area.  It's more like staining, can be seen but only barely perceptible to the touch.  Wetsanding and polishing removes most of it leaving behind what I believe to be very fine pitting, again can be seen but not felt.  The crowns and ring lands are in good shape, most of this is going on in the lower third of the skirt.

Would you use these pistons?

The one on the left is untouched, the one on the right has been cleaned up.

Thanks

mystic_1

[mystic_1]

Next, I find myself frowning at the primary chain gears on my crankshaft and primary shaft sprocket.  They're definately showing some wear.  I'd planned on new chains and a new tensioner anyway, but I'm not pleased with the wear on these teeth.

I know that a new chain would wear faster on these teeth, but would it be out of the question to re-use these?  Would you?

thanks,

mystic_1

[mystic_1]

Oh, here's why I'm replacing the pistons

mystic_1

[heffay]

pistons looked ok until that last pic.  the rings are what touch the cylinder walls and the pistons are not meant to.  until i noticed the brokenness i would have polished and reinstalled.

i don't know about the sprockets... are those normally squared teeth on their top edges?  if so i would replace. 
there isn't lopsided wear on one side of each tooth as i can see?  how 'bout on your end of the camera?

[mark]

pistons looked ok until that last pic.

+1

The sprockets on the crank are part of the crank and to replace - you replace the crank. The pic of the driven sprocket doesn't look that bad from here. You might want to change the rubber damper bits inside.

[BSA_Mikael]

I would replace the pistons, they are not expensive if you compare to the result of using bad ones.. I would replace both the chain and the sprocket on the camshaft, like with the pistons that is not too bad with regards to price. As for the crankshaft, i would take it to a friendly mechanic and ask his opinion, because THAT is expensive.. Normally, if the bike is driven hard with bad or too little oil, the camshaft and cylinder head is what takes the first hit.. With a little luck, the crank and its bearings made it through..

Best regards, Mikael

[kghost]

I would replace the pistons, they are not expensive if you compare to the result of using bad ones.. I would replace both the chain and the sprocket on the camshaft, like with the pistons that is not too bad with regards to price. As for the crankshaft, i would take it to a friendly mechanic and ask his opinion, because THAT is expensive.. Normally, if the bike is driven hard with bad or too little oil, the camshaft and cylinder head is what takes the first hit.. With a little luck, the crank and its bearings made it through..

Best regards, Mikael

I think if he's got it this far he IS the mechanic...

Seriously don't go ask some bozo who knows nothing about old hondas....your at the right place...


Pistons (except the broken one) look fine to me from what I can see...the ring groove area is critical as is piston pin wear ...can't see alot of those areas in your picture.

Crank looks usable....yeah theres some wear but are ya gonna ride it 100,000 miles?

[mystic_1]

Yes I'm the mechanic

I'm hoping to re-use the crank, but already plan to replace the primary chains and tensioner.  I'll probably look for a better driven sprocket, think I have the one from my 73 parts motor here somewhere.  Will have to conduct a search & inspect mission.  The cam chain tensioner, guide, and gear are all new - replaced them some years back and they're still in good shape.  I'm planning on upgrading the cam chain to the stronger one sold by Cyclex.

I've been frowning at those pistons for a while now, the only reason I'm even considering them is because I already have them, I'm still 50/50 on them.  The ring groves look good to me, I have to scrutinize the wrist pin holes yet, but I wanted to see if the oxidation was even removable first.

Thanks for your opinions, I'd appreciate any more comments anyone wants to make.

mystic_1

[heffay]

once the piston has been damaged like that there is no telling where a stress crack might be.
i wouldn't.
i grenaded two pistons simultaneously in my first car.  maybe it was because they were already damaged.   maybe it was because my foot was thru the floor.  see what i mean?
i'd hate to question a trashed motor over what is not now.

[edit]  i almost forgot... it was a fairly low mile rebuild on a 6.6L trans am motor 

[mark]

i grenaded two pistons simultaneously in my first car.  ... it was a fairly low mile rebuild on a 6.6L trans am motor 

That's how Pontiacs show gratitude.

[mystic_1]

If you're talking about the last pic with the damaged skirt, yeah that's unquestionably in need of replacement.  That's one of my original pistons.  The other three are fine but I need to either find an exact replacement or replace them all as a set.  This is why I'm looking at the '73 pistons as replacements.

The damage was the result of this piece:



which was originally a part of one of the Final Driven Shaft bearings (the outboard one).

One day while riding, there was an event of some sort where I suspect I sucked something through the chain while riding.  This resulted in two things, the crankcase broke:



and, I found out much later on, that chunk broke off the final shaft bearing race:



and began a walkabout through the innards of my engine.  I've found marks indicating it passed through the transmission, the primary drive, got chewed on by the piston pictured above, and finally came to rest in the crankcase sump below the crank where it remained until I disassembled the motor.

I've got some replacement cases on the way and am currently evaluating the rest of the parts.  So far the transmission shafts, gears, and so forth seem good, the above parts are the most questionable.

So thanks for the comments everyone, I'm still on the fence about using the 73 pistons but you've all given me a lot of food for thought.

mystic_1

[754]

I would check the chain on the sprocket, put a 1/2 wrap on it and see how far it lifts away..try moving the chain back & forth to see if there is sprocket wear.

 A bit hard to do witout a new one to compare, but teeth dp not look bad.

 That bearing chunk.. never seen that but shows how much stress is on the output shaft when a chain piles up.

[bwaller]

The pistons may look good after you're sanded & polished them, but take some measurements to really know. If they have miles on em I think it is money well spent to go new.

There have been many cases welded in that area so that is an option if you have all the pieces. If your crank bearrings are good and you can have a weldor fix the cases it may be less money and aggravation than replacing bearrings in another set of cases.

The sides of the primary sprockets seem "polished" by the chains but the teeth look ok. Like 754 said tighten a new chain over them and check for play.

Diasassemble & check your oil pump and while your at it pull the oil tank and make sure its clean too. Bits of steel and aluminum can come to rest in the strangest places.

[mystic_1]

The pistons may look good after you're sanded & polished them, but take some measurements to really know. If they have miles on em I think it is money well spent to go new.

That was the other reason I polished the one piston.  It measures well within spec after cleaning.  Unless I find something seriously wrong, I'm currently leaning towards proceeding with these pistons.  The left piston in the first pic of this thread is the worst one of that set, the other have much less oxidation and seem to be in otherwise fine condition.  The motor they came out of seems to be fairly low-milage but i got it as a parts motor and don't really know how many miles it had on it.  The rest of the parts from that motor are in good shape wear-wise.

There have been many cases welded in that area so that is an option if you have all the pieces. If your crank bearrings are good and you can have a weldor fix the cases it may be less money and aggravation than replacing bearrings in another set of cases.

Yeah, this case had already been broken and welded when I bought the bike.  Both the top and bottom case had been re-welded.  The new damage is also to both case halves.  Examining the damage, I see a network of cracks at the perimeter of the depressed area.  Currently the pieces are still in place, all the metal is still present.  I can see that it would take a tig-welding artist to restore the case, so I've located a different K0 crankcase and will sit on the broken one until I can get it sorted some day.

     

Diasassemble & check your oil pump and while your at it pull the oil tank and make sure its clean too. Bits of steel and aluminum can come to rest in the strangest places.

Good advice.  I'm currently in the "no two parts bolted together" stage and the oil pump has already been rebuilt.  Just before I took the bike down for the rebuild I drained the oil - it came out with bright silver streaks from where a tranny gear was grinding away the damaged case from the inside 




Every single part in the motor is being cleaned and inspected before anything goes together.  On closer examination I don't think the teeth on the crank and driven sprocket are as bad as I thought at first, I'll check them with a new chain once I get one in.

mystic_1