OM617 main bearing crank condition - 2nd, 3rd, 4th... opinion required - Page 2 - PeachParts Mercedes-Benz Forum

DocSarvis · #1 10-12-2010, 09:25 AM

I agree with the finger nail method for a better check than visual. If you feel the grooves it wont polish out for good results. you want about 1-3 thou between the bearing and crank. anymore than that it will start to knock. A typical human hair is 3 thou so if you "polish the grooves out you will be undersized. Not good. A shop can turn it down 10 under and then you can get 10 over bearings and be fine. hand polishing will only take abot 1/2 thou out and that will still leave the grooves if you can feel them. Dont build a compromized motor. Have it turned down should be relatively cheap Less than 100$ I would think. Thanks

Stretch · #2 10-12-2010, 09:47 AM

Quote:

Originally Posted by DocSarvis

I agree with the finger nail method for a better check than visual. If you feel the grooves it wont polish out for good results. you want about 1-3 thou between the bearing and crank. anymore than that it will start to knock. A typical human hair is 3 thou so if you "polish the grooves out you will be undersized. Not good. A shop can turn it down 10 under and then you can get 10 over bearings and be fine. hand polishing will only take abot 1/2 thou out and that will still leave the grooves if you can feel them. Dont build a compromized motor. Have it turned down should be relatively cheap Less than 100$ I would think. Thanks

Hi Doc(Sarvis) I've still not worked out if you like being called Doc or not!

Unfortunately the cost of machining here is pretty daft. I'm guessing they'll expect about 40 euros per journal. I have heard rumours that a new OM617 crank is about 500 euros - but they are no longer obtainable via the dealer... If I can get a new crank for this kind of cash then I'll probably go for that instead of encouraging the silly labour rates here - and when I go back to England I can get my existing crankshaft refurbished for a reasonable rate and then sell my old crankshaft back here for a silly price (It is all a bit tedious but that's what you have to do to get things done for a reasonable amount here)

DocSarvis · #3 10-13-2010, 07:08 AM

Yes I go by Doc, I knew it was you but forgot you weren't stateside. That changes things as you pointed out. As long as you can keep the clearance in the 3 thou range clean away. I would run grooves before I would undersized. with new bearings or even the old you should have life left. Not as much life as a machined crank but still good life. Good luck. If nothing else bum a set of Mics and measure the journals yourself. Thanks

W124 E300D · #4 10-13-2010, 07:33 AM

Two things.

1. Micrometer handled by someone who knows how to use it (after reference-ing) is the ONLY way to go. Everything else is guesswork.

2. Unless mic readings and visual inspection were "like new" spec, once the engine is in bits grind the damn thing and fit new shells**, it just doesn't cost that much and it will last 250k miles if done properly.

** don't forget the rest of the lube system, oil galleries, sludge traps, oil pump itself, relief valve, etc etc.

The words "False economy" spring to mind.

Stretch · #5 10-13-2010, 08:03 AM

Quote:

Originally Posted by W124 E300D

Two things.

1. Micrometer handled by someone who knows how to use it (after reference-ing) is the ONLY way to go. Everything else is guesswork.

2. Unless mic readings and visual inspection were "like new" spec, once the engine is in bits grind the damn thing and fit new shells**, it just doesn't cost that much and it will last 250k miles if done properly.

** don't forget the rest of the lube system, oil galleries, sludge traps, oil pump itself, relief valve, etc etc.

The words "False economy" spring to mind.

False economy indeed - but see my posts above regarding Dutch labour rates - it might work out to be cheaper to buy a new crank! I'm still investigating this option.

I have no intention of chucking it all back together (and I don't think that has been suggested: measure measure and measure seems to be the message) - that would be like being scared to jack up your car because you think it is too rusty - I'm definitely of the opinion that you do some something right the first time - and then hopefully you won't need to do it again. If you, however, do need to do it again at least you won't be kicking yourself because you know you did a pants job in the first place...

W124 E300D · #6 10-13-2010, 08:13 AM

Quote:

Originally Posted by Army

False economy indeed - but see my posts above regarding Dutch labour rates - it might work out to be cheaper to buy a new crank! I'm still investigating this option.

A new crank STILL needs to go to a shop, to be checked, both for tolerances and for "true".....

Ask me how many "new" cranks I have seen that were not "right"...

Stretch · #7 10-13-2010, 09:02 AM

Quote:

Originally Posted by W124 E300D

...

Ask me how many "new" cranks I have seen that were not "right"...

So how many new cranks have you seen that weren't right?

W124 E300D · #8 10-13-2010, 11:21 AM

Back of the envelope...

1 in 20 with some sort of damage or defect, e.g. been dropped at some time while in stock and so bent.

1 in 20 technically within the + or - limits, but so close that it was worth exchanging them for another one rather than trying to either correct or just fit.

1 in 20 "made up" (not one piece forgings) with big ends "timed" out 0.5 degrees or more (e.g. 120 degree triple with the big ends actually at 0, 121, 240 degrees)

1 in 20 with non-uniform filleting / radius's.

1 in 20 with QA failures, e.g. oil galleries and sludge traps with swarf / burrs / defects / dirt somewhere in them.

Seen some with more than one of these faults at a time.

The ONLY 100% defect free, perfect, high tolerance, fully machined cranks I have ever seen that needed ZERO fettling of any kind, just oil them up and fit, are Japanese motorcycle pressed up cranks with needle rollers... they all look like parts from a swiss watch.

If it was me and I was that far into the job that the crank was out, I'd get the turner (grinding machine tool operator) to *FULLY* clean, dress up and grind and required, fettle all non machined surfaces (bead peen) and dynamic balance. Talk to them nicely and ask for a written report with hand taken measurements of each journal AFTER the job is done.

I'd then hand fit and number every shell with prussian blue... final fit drowned in lube, cranked for 60 seconds with injection pump rack closed until you get full oil pressure, then start.

None of these jobs are hard or time consuming once the engine and crank is out, once they are back in, it's too late.

get the turner / grinder to supply the shells, you require the correct amount of difference between the hardness of the journals and the hardness of the shells.

W124 E300D · #9 10-13-2010, 08:12 AM

Labour?

You NEVER take (for example) an MB crank to the MB dealer, they will outsource it anyway.

Find your local commercial vehicle independent shop, ask them who the best local crank grinding shop is, go to them direct, should be around 20/25 euros per journal...

TOP TIP.

NEVER tell a tradesman (eg turner) his job, it will cost you extra, go in with the crank, go in with CLEARLY PRINTED (make sure your numbers are correct for the part number) OEM dimensions and tolerances, show him both, ask his advice, follow it.

If you go in and basically tell them what to do, that is what they will do.... sometimes, just sometimes, this is what the turner would actually advise you to do, every other time you just increased your bill...

Johnt49 · #10 10-13-2010, 03:22 PM

If you have the crank reground it will have to be nitrided again or the journals will be softer than they are now. Take a piece of 400 wet/dry paper cut it to the width of the journal then wrap it around once & tape it together. Then use a flat shoe string wrapped once around the paper with the ends pointing out in opposite directions. Pull back & forth on the ends creating a rotating motion on the 400 paper.This will polish the crank enough to knock down any protruding material & leave a smooth enough surface for your bearing (400 grit is what most machine shops use to polish cranks after grinding). I prefer using the paper dry so the debris is easy to blow off when you're done. Be sure to clean the oil passages in the block & crank when you're done so there's no grit in there to tear up your new bearings.

Stretch · #11 10-14-2010, 04:00 AM

Quote:

Originally Posted by Johnt49

If you have the crank reground it will have to be nitrided again or the journals will be softer than they are now...

...I prefer using the paper dry so the debris is easy to blow off when you're done. Be sure to clean the oil passages in the block & crank when you're done so there's no grit in there to tear up your new bearings.

Great tip - thank you

layback40 · #12 10-14-2010, 06:57 AM

Army,
I am a little concerned that its starting to be a mountain being made out of a mole hill !!

You will see that Roy (whunter) suggested that it didnt look too bad & you should have it checked with a micrometer.

I would respectfully suggest that he is probably the best person to listen to bar no one on this site when it comes to diesel motors. I would put his opinion above mine and any one else on here.

When you have the results of the measurements, post them on here, then they can be compared with specs & appropriate advice given. Until then, any advice on here needs to be taken with a grain of salt !!

The last things I would want to see happen is either you put a bad crank back in your motor or you unnecessarily buy a replacement crank.

I look forward to reading the measurements of each journal (main & rod end).

It is also very important to determine that the crank is straight & true.
I normally do that by placing the crank back in the block without the last 2 or 3 mains & using a dial gauge to check if the unattached journals are true.
It shows a bent crank.
You can then repeat with different journals unattached.

Hope that helps.
Looking forward to seeing the results of the mic on the journals.

Good luck !!

Stretch · #13 10-14-2010, 07:13 AM

Hey layback40 - thanks for the concern. The crank is still at the machine shop at the moment. They said they were going to measure it. I'll see what they come up with first - it is a bit late to jealously snatch it back and do some measurements of my own first!

As a learning exercise I'll measure the crank when I get it back and I'll definitely do the "is it bent" check you suggest. I see no harm in extra non-destructive testing.

I was only considering buying a replacement crank because it might be cheaper than paying for labour here - IT IS MAD MAD MAD HERE! I still don't have a price though and if the new crank needs machining then that's a waste of time anyway...

I'll probably post the measurements next week. Thanks.

layback40 · #14 10-14-2010, 07:44 AM

Army,
If they are a good shop, they will give you ovality, runout & surface imperfection measurements on all journals.
I suspect a new crank would be well over 1k euros.
diesel cranks generally fail for a reason (I dont believe yours has failed). As they are so hard, they dont ware so much like gasser crank bearings.
Have you checked the oil pump for end float & clearance? A good oil pump is far more important than a few marks on a crank journal. If its chain drive, a new chain is good insurance.

Stretch · #15 10-14-2010, 09:12 AM

Quote:

Originally Posted by layback40

Army,
...
...Have you checked the oil pump for end float & clearance? A good oil pump is far more important than a few marks on a crank journal. If its chain drive, a new chain is good insurance.

The machine shop bloke said I needed to replace the brass coloured bushings on the shafts that drive the oil pump so that is hopefully being done as I type - I'll look in the FSM for oil pump end float information - thanks.

I've already got a new chain but I'm sticking with the old cogs - they seem fine to this bicycle repair man!