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James H

Repairing broken piston and con rod on K181S

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James H

Commando 800
Model: K181S
Serial No: 9514046
Spec. No: 30700d
 
Hi
 
I have just joined as I have a rebuild to do on my Wheelhorse, the con rod and piston broke and require replacement, I couldn't find original parts so have a kit from ebay seller in the States
 
I think I have everything I need apart from knowledge! To begin with the crank is not super smooth, I am wondering if that will be a problem? I have taken a short video which shows the state of it.
 
The video is here 


 
Any advice will be much appreciated!
 
Thanks
James

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Pullstart

ohh that's not good.  You might want to either take it to a machine shop to clean up that crank, or look for a reasonably priced clean used crank.  otherwise you'll tear up your new rod as soon as you fire it up!

 

and Welcome to RedSquare from the States!

Edited by pullstart

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James H

I was afraid that might be the case!

 

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rmaynard

If the kit you bought includes a standard size connecting rod, you may have to try to send it back if the crankshaft needs to be turned and an undersized rod fitted to it.

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Pullstart

I just built up a similar engine following RMaynard's 857 build thread 857  just make sure that you install the governor cross shaft during the governor setup!  Otherwise have a clean working area and take your time, it's fairly simple.

 

most the junk on the crank is probably the old rod's material so you may or may not be able to clean it up with the standard sized rod.  make sure to mic it before you assemble it to be safe.

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James H

Thanks pullstart,

 

How would you recommend cleaning it, I'm new to this!

 

James

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rmaynard

It's just aluminum alloy pulled from the rod bearing surface. When you take the crankshaft out, you can soak the journal in muriatic acid (available at Home Depot in the paint department). That will remove the aluminum without hurting the crankshaft journal.

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James H

Thanks, that sounds like a good option. Is it likely that the crank could have been distorted by the impact of the rod when it failed, would you advise replacing the crank anyway under these conditions or is it unlikely to have been damaged further that what is visible?

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meadowfield

that galling looks bad, does it scrape off?

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James H

I haven't tried, I was worried about damaging it. Am I being over cautious?

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WH nut

Clean it up with acid and emery paper, mic it to make sure you have the right clearance and run her. I see them like that all the time and have yet to turn a crank.

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Theroundhousernr

   Dont scrape anything...... Get some muriatic acid. Apply it only with a Q tip to the aluminum in a well ventilated area. Keep wiping it off and adding more. You only need a little. I would not soak it. It creates extremely strong fumes so you do not want to breath it in.  Do this OUTSIDE!! Wipe some oil or grease on all the machined surfaces of the crank because the fumes will instantly start to rust any surface near it. Take your time. If you see black , its still aluminum. Keep going till you dont see any fizzing anymore.

 

 You must nuetralize all the acid after you feel you got all the aluminum off. I dunk the crank in water in a bucket with a cup or so of baking soda to make the water alkaline. Then rinse with the hose some more.Then lightly polish with green scotchbright pad cut in strips with some oil as a lubricant. Finally oil the whole thing well and stick it in a bag till your ready to use it. 

 

  PS For future reference ... never order parts till you have everything all measured either by you or your local machine shop. They usually do it for free...... Your doing good and glad you took the time to tear into it and not throw away.

Edited by Theroundhousernr
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Theroundhousernr

Here is one I just cleaned up for my rebuild coming up.

 

Before

5y6epepu.jpg
 

 

After
agezudu2.jpg

 

 

 You sound a little green to small engine rebuilding.... Please remember to hone the cylinder before installing your new piston and rings. Boy, have I heard that story plenty of times. Wonder why it is low on compression and burns oil worse then before.... You might say duh... I already know that but I am just being sure.

Edited by Theroundhousernr

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James H

Thanks for the tips everyone, I will try to find some acid later toady, I'm not sure what it's called in French, is it a diluted Hydrochloric acid?

 

Hone the cylinder, what does that mean?!

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rmaynard

Muriatic acid is hydrochloric acid. It is diluted. Honing a cylinder is a process of removing the glaze from the cylinder by using rotating stones or balls on the end of a drill. See my thread on the 857 refresh/rebuild.   I used a "ball hone" as pictured in the thread.

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James H

Thanks, I will have a look. I used the acid/scotchbrite technique, just finished in fact, I was amazed with the results. 

 

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James H

Here it is 

 

Can you recommend a micrometer for me please?

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Pullstart

that looks great!  any 1-2" (or 25-50 mm?) micrometer will give you the information you need.  Most have a calibration rod that comes with the set, so get used to feeling of your "zero" point to not stretch your mic.

 

just think - if you need to buy tools to save money on your tractor, what better way to get more tools?

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James H

That's a good point pullstart! Thanks

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James H

I have just fitted the con rod to see how snug it is, as you can see from the video, not very snug at all. I'm assuming it's meant to fit better than that?

 

http://youtu.be/z_ocWob5Guo

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Molon_Labe

I have just fitted the con rod to see how snug it is, as you can see from the video, not very snug at all. I'm assuming it's meant to fit better than that?

 

http://youtu.be/z_ocWob5Guo

 Ouch! You are right, that is way too loose. As stated above, get a micrometer and check the crank journal size. From the looks of what you have there it looks like the crankshaft may have been turned down in the past and if that is the case it would measure around 1.175 inches or 29.845 mm for .010 undersize.

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James H

Thanks, I have ordered a micrometer to check, that was the assumption I came too as well, hopefully it's that simple!

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Fordiesel69

STOP!!!!

 

Do not go any further with that crankshaft.  It is considered scrap at this point.  You **MIGHT** be able to get a machine shop to go as far as 0.20" undersize, but the quilaity of these rods are not verified, and the durability of the crankpin will be in question.

 

You might want to have a mahine shop check it, and maybe just replace the crank with a used on off ebay.

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slammer302

I may have one if you decide to scrap that one

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James H

Why is it scrap, could it not be that it has been turned already and I need an oversized con rod? Slammer, do you have one?

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