Author Topic: Crankshaft wear (and pistons)  (Read 230 times)

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Backoftheshed

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Crankshaft wear (and pistons)
« on: October 16, 2018, 02:14:24 PM »
Hi Everyone,

I've been making assessments of my engine to determine which path to follow.
I took measurements today to work out the crankshaft journal sizes and pistons as well.
Then of course it occurred to me that I could have just looked at the bearing shells.. ::)

Anyway, my calculations led me to believe that the crank had already been ground before as I figured it was 30 thou undersized. It was nice to know that milking cows for a new lifestyle hasn't dulled my brain, the bearing shells confirmed my maths.
In the image below you can see 2 journals i checked (they were both the same). The one on the right is number 2, the cylinder that has the burnt piston and number 3 next to it.


My crank question is, what level of 'damage' determines another regrind and what can be 'got away with' by just polishing?



The other question is if anyone can 'decode' piston markings. The code on all of them is M2039 C9. There is no STD or obvious oversize stamped in. Im assuming that they've been done before if the crank has been ground before.
I don't yet have gauges in my toolbox to make proper bore measurements..

Grateful for your input as always..

Cheers
Chris

winabbey

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Re: Crankshaft wear (and pistons)
« Reply #1 on: October 20, 2018, 05:36:02 PM »
Can't help with a specific answer, but a search on M2039 piston brings a few hits on Google and one on here (see below). I'm guessing the Google hits will help identify the make and size of piston you have.

https://www.mokeforum.com.au/index.php?topic=6605.msg74470#msg74470

Backoftheshed

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Re: Crankshaft wear (and pistons)
« Reply #2 on: October 27, 2018, 01:47:19 PM »
Thanks,

I read that entire post and although the question about the pistons was never answered, later on, reference was made to the engine being bored from standard to 20 thou, so that would infer that the piston markings were just standard size.
That would match the measurements I managed to take suggesting they were standard too.
Since my original post, a decision was made to get it machined anyway.
With one bore very slightly marked from light surface rust in one spot, the wear as well, and uncertainty about crank wear (pins are 30 thou o/s and main bearings 10 thou o/s, it seemed a bit of a waste of time to just whack it back together with a few new bits. That and my end float was out because one thrust bearing had NO copper on it at all and has put a slight lip on the crank web.
Just got to find some $$ now..  :-\

Cheers
Chris

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Re: Crankshaft wear (and pistons)
« Reply #3 on: October 27, 2018, 09:03:18 PM »
Hi Chris,
I think youve done the right thing by setting the base line for your engine. Its the "not sure" things that will trip us up in the end.
Its not uncommon to find the thrust bearings rat shit  ;). Heavy traffic situations where your stuck at traffic lights a lot and leave it in first gear with the clutch keeping pressure on them will surely wear them out quick smart. For me, clutch is for gear change only, not sitting there idling with it in.
HP
Experiencing the Baader-Meinhof phenomenon.
"As a Moke owner, you have a heightened awareness of Mokes in your environment, they were always there." 

https://www.mokeforum.com.au/index.php?topic=4727.msg161920#msg161920