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  #1  
Old 06-07-2007, 10:55 PM
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Location: Oklahoma
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'72 250 engine rebuild underway

I have the entire bottom end of my M130 engine torn apart - just got done reaming the cylinder bore ridges - time consuming but definitely got the hang of it as I went along. I have honed 2 of the cylinders and they look pretty good, although keep in mind I don't have much to compare it to. I have micrometered them several times from a variety of spots and all measurements are within specs (86.5 mm), so I think my bores are in good shape. I have purchased new rod bearings and main bearings, new Deves piston rings and I'm getting close to reassembling.

One question - should I change all of the timing related stuff- camshaft gear, idler gear, crankshaft gear, timing chain, guide rails? My mechanic friend is recommending that, especially after looking at my camshaft gear, which he said had pretty sharp teeth on it. Is this one of those 'while you're there' things, and if you change one part you should just change them all?

And can anyone verify which main bearing is the thrust bearing? There are seven total main bearings in this engine.

Ryan

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1984 300D
1972 250
1986 560SL
1991 300CE
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  #2  
Old 06-07-2007, 11:13 PM
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Join Date: Dec 2006
Location: beautiful Bucks Co, PA
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The thrust is taken by a saddle type main bearing. The bearing web/cap it sits on will be machined on both sides. I doubt you can fit it easily into the wrong position.
Any sprockets that have very sharp or under cut teeth should be replaced. Guide rails on this engine seem to last forever, replace if pitted. if you replace any sprockets, replace the chain also.
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  #3  
Old 06-07-2007, 11:14 PM
t walgamuth's Avatar
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Join Date: Apr 2005
Location: Lafayette Indiana
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the thrust bearing will have a big flange perpendicular to the crank line.

your friend is correct. if the teeth are looking sharp that is a sign of wear. you can also look at the teeth and see clearly if they are symmetrical or not. if they look like waves on the ocean that is a sign of wear.

you can also look at the chain and see how much wear there is visually. i am not expert at this but i think you just look at the end play on the rollers and the amount it will bend from side to side. it should want to stay very straight. being able to bend the wrong way is a sign of wear on the bearing point of the little axles.

probably should replace the cam chain guides too.

good luck

tom w
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Old 06-08-2007, 10:02 AM
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Gentlemen, Thank you for your replies - any advice or cautions is desired here - appreciate the input.

I should have made my thrust bearing question clearer - I know which bearing is the thrust bearing and I know that it was at the number three bearing (from the front of the engine working back - I left all of the bearings in the caps, just in case). My mechanic friend was just wondering about it's placement for sure - to him it looked like it belonged at number 4 instead??

Ryan

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1984 300D
1972 250
1986 560SL
1991 300CE
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