small-end (wrist-pin) wear

beauchemin

beauchemin

Senior member
Location
Victoria, British Columbia
I am continuing to dismantle my motor.  I've checked the small-end play and both outer cylinders have noticeable rocking of the wrist-pin in the vertical axis, with no noticeable play in the horizontal plane (front to rear movement is nil).  The middle wrist pin has similar noticeable rocking both in all directions.  Mileage is @ 50,000 kms.

I'm doing a rebore and getting new pistons, so I want to get the job done correctly.  I think I may need to replace the wrist-pin bushings.  Any input?

If I need new bushings, does the crankshaft need to be dismantled to correctly replace the wrist-pin bushings?  My concern is that getting them reamed perfectly square, parallel to the crankshaft, will be difficult if done by hand with the crankshaft sitting on my workbench.
 
If I need new bushings, does the crankshaft need to be dismantled to correctly replace the wrist-pin bushings?  My concern is that getting them reamed perfectly square, parallel to the crankshaft, will be difficult if done by hand with the crankshaft sitting on my workbench.
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Hello,
opinions differ about that. I've replaced and reamed them on the complete crank, even with the crank still in the engine.
I've made myself a tool with a larger bush and a threaded rod, that allowed pulling the new bush
into the bore and at the same time pressing the old  one out. No punches here!
I think the trick at reaming is to take only a very small amount off pass by pass to stay parallel.
Don't forget to bore it through the little hole in the rod.

hth
Ernesto
 
They can be removed and replaced in situ but it is not recommended. There are two potential problems, first one is sizing the new bushes, I make them a bit under size and hone them to give the correct clearance which is impossible on an assembled crank the second problem is I occasionally find the small end eyes on the rods have gone a bit oval. They then require boring and honing to clean up back to round and a bush made to suit the new small end eye dimension. My advice would be to actually measure what you have and compare it to the factory figures for acceptable wear, if everything is within tolerance then leave the lid on the worm can.

  Keith.
 
laverdakeith said:
They can be removed and replaced in situ but it is not recommended. There are two potential problems, first one is sizing the new bushes, I make them a bit under size and hone them to give the correct clearance which is impossible on an assembled crank the second problem is I occasionally find the small end eyes on the rods have gone a bit oval. They then require boring and honing to clean up back to round and a bush made to suit the new small end eye dimension. My advice would be to actually measure what you have and compare it to the factory figures for acceptable wear, if everything is within tolerance then leave the lid on the worm can.

  Keith.
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+1 (bigthumb)

The factory type of bushes actually allows for slight imperfections in the conrod, the extremely soft outer steel bearing metal carrier is very malleable.  Any out-of-squareness/roundness is compensated for when boring/reaming, as there is more than enough bearing material in there that can be removed.

Came across a triple rod recently in which the stock bush had turned for some obscure reason, small end eye was worn over limits to accept a new stock bush, needed to make a new one.

piet
 
50,000k seems pretty low to be looking at small-end bush replacement. I'd be extremely wary of reaming in-situ as even a miniscule degree off square and you'll be creating dramas with side-thrusting on the big end of the rod and web journal (been there, done that, with the crank out). Sometimes a new gudgeon (ie wristpin in old lingo) will close up the play somewhat - unless you can hear it  knocking  :o  if pulling that crank apart is not an option, I'd leave it as is. 

Last time I had my SFC rods out I had them checked and straightened (ie paralleled and centred big to small end). As the sating goes, 'Do it right, do it once'.
 
Alright, I measured the small ends last night.  The wrist pins are 19.98mm (within spec), and the two outer bushes are ovalized, with vertical measurement 20.05mm.  The manual says that a maximum of .05mm clearance is allowed, which means I'm farked, right?
 
beauchemin said:
Alright, I measured the small ends last night.  The wrist pins are 19.98mm (within spec), and the two outer bushes are ovalized, with vertical measurement 20.05mm.  The manual says that a maximum of .05mm clearance is allowed, which means I'm farked, right?
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Hi Chris

this bike is a keeper, right....?

if so, then the small end bushes need fixing. To do that well and properly the crank needs to come apart. If the crank is apart and the rods are out, "while you are at it you might as well" fit a set of Carillo rods and new crank bearings....... 8) ;) :'( :-X ::)

the kids just will have to go without new shoes for a bit, that's all..... ;)

Paul LeClair

ps - in all seriousness, while the bushes are at the far end of the serviceable range, to avoid spending the additional funds on an already WAY over budget build, nothing wrong in my book with putting it back together "as is" and doing it next time the motor comes out and apart, it will run for a very long time yet "as is".
 
Paul LeClair said:
Hi Chris

this bike is a keeper, right....?

if so, then the small end bushes need fixing. To do that well and properly the crank needs to come apart. If the crank is apart and the rods are out, "while you are at it you might as well" fit a set of Carillo rods and new crank bearings....... 8) ;) :'( :-X ::)

the kids just will have to go without new shoes for a bit, that's all..... ;)

Paul LeClair

ps - in all seriousness, while the bushes are at the far end of the serviceable range, to avoid spending the additional funds on an already WAY over budget build, nothing wrong in my book with putting it back together "as is" and doing it next time the motor comes out and apart, it will run for a very long time yet "as is".
Click to expand...

It's going to really bug me putting it all back together with the intention of doing it properly "next time".
 
beauchemin said:
Alright, I measured the small ends last night.  The wrist pins are 19.98mm (within spec), and the two outer bushes are ovalized, with vertical measurement 20.05mm.  The manual says that a maximum of .05mm clearance is allowed, which means I'm farked, right?
Click to expand...

No it means you are at the limit of what the factory quote as being acceptable. Have you measured the old gudgeon pin or the new one? I rebuild engines for other people as part of my full time occupation, not every job is an open chequebook affair so judgements about how to proceed must be made based on measurements and experience.
  Take a piece of wire and poke it into one of the crank slingers, if the crank is clean, runs true, is in phase and the main and big end bearings feel good then run with your little ends as they are. If the crank is full of shite, running pissed or out of phase then press it apart and do the whole job top to bottom, give up smoking/drinking/whoring or whatever else may absorb your spare cash for a month and splash out on some Carrillo insurance while you have it apart.  ;)


    Keith
 
laverdakeith said:
No it means you are at the limit of what the factory quote as being acceptable. Have you measured the old gudgeon pin or the new one? I rebuild engines for other people as part of my full time occupation, not every job is an open chequebook affair so judgements about how to proceed must be made based on measurements and experience.
  Take a piece of wire and poke it into one of the crank slingers, if the crank is clean, runs true, is in phase and the main and big end bearings feel good then run with your little ends as they are. If the crank is full of shite, running pissed or out of phase then press it apart and do the whole job top to bottom, give up smoking/drinking/whoring or whatever else may absorb your spare cash for a month and splash out on some Carrillo insurance while you have it apart.  ;)


    Keith
Click to expand...


That is a lot of whores Keith  :-X

Paul
 
I ran my first Laverda for the best part of 100,000 miles without all this soul searching. I had no money so I had to make do. The bike always went like stink and although it felt a bit 'loose' in the small end department, it didnt really cramp it's style much. Just enjoy it.
 
My motor did 170k kays before I just did the complete rebuild. I put new rings in 50k kays ago and back then the ring gaps were at maximin tolerance. It still went like the clappers and the only sign was some smoke out the zorst. They are pretty robust motors. On this current rebuild I never intended doing the crank. I got a guy to install and reem [insitu] new little ends and he totality fucked them up so it was crank out and off to Red's. This is one occasion I'm glad the guy fuck up as I can now sleep easy knowing the bottom end is way better than it left the factory.
According to Red the slingers were full also.
 
3patC and motoddrob -- you gents make good points.  The main reason I'm fussing about this is because the rest of the top end will be 100% new.  I know that I could just put the old pistons back in with new rings and a hone job, and leave the small ends alone.  It would run OK.  However, I want to be able to rev it hard without worry.

One can also view a crank rebuild as an expensive type of crankcase insurance (there is only one set of matching cases?) with the added bonus that everything will run just as, or better, than new.
 
                                                            "One can also view a crank rebuild as an expensive type of crankcase insurance (there is only one set of matching cases?) with the added bonus that everything will run just as, or better, than new."

For this reason alone a crank rebuild is worth the expense in my opinion. If it's out of reach financially, sell you children or even worst get a 2nd job :o
 
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