Crankshaft thrust bearing wear

[Charles 230SL]

Yesterday I discovered that I have excessive lateral (fore/aft) movement of the crankshaft on my 230.  I didn't measure the lateral movement but it well exceeds .004".  This is an early 230 with the original engine (127981-01-003227). As best I can tell, the lower-end has never been overhauled and these are the original main bearings. The engine runs great and has strong oil pressure. Needless to say, this ruined my day.
I read from an earlier post that the early engines had thrust bearings attached to the #3 bearing cap.  Is it possible to remove the bearing cap and replace the thrust bearing without pulling the engine and dropping the crankshaft? thanks, Charles

[ja17]

Hello Charles,

The center thrust bearing is just accessible after removing the lower steel oil pan. If your is the early style, it may have the individual thrust bearing inserts pinned to the third main bearing cap. In this case you may want to find an oversize set and just fit the new thrust bearings.

In case you use the newer bearing with the thrust built in, yo would need to fit the bearings to the crankshaft thrust surface and the main cap.

This can be done with engine in the car. The oil pump would have to be removed also.  Hopefully the crankshaft surface is still in good shape. If you attempt this project keep us up to date.

[Charles 230SL]

thats good news, thanks Joe.
I'll need to confirm whether the engine has the thrust bearing inserts - hopefully it does.  I presume there's no thrust surfaces on the top half of the third main bearing.  I've overhauled my share of engines over the years but this is the first time I've seen thrust bearing surfaces (only) in the bearing cap. I'll keep everyone posted.
thanks again Joe.

Merry Christmas all, Charles

[Benz Dr.]

Main bearing caps usually won't go out of round like rod bearings will but I wouldn't try what you plan to do.  The replacement bearings are all one piece and are generally .010'' wider to allow for crank grinding. I've never had to replace standard bearings so I'm not sure if they also make them wider but you will find that the old three piece bearings may have pins on the cap and block to hold the thrust washers in place. You will need to remove the pins by grinding them off so that the bearing will fit into place and you will need to remove the crank to do this. Even if there are no pins ( I believe are none ) you will have to buy a full set of bearings anyway so why not do it right.

Another thing to consider is the old bearings tend to wear a certain way and the new bearings may run tight because of this. The thrust bearing may be wider and it will need to be sanded down to fit the .004'' end play you mentioned. Remove material only on the back side of the main locating bearing so that a true running surface is facing forward on the crank. The crank will tend to pull forward while the engine is running so this will provide the best solution.

If you have good oil pressure, this end play may not be as big of a problem as it seems. I have engine number 000161 which also has standard bearings but we plan to install .25mm bearings in it. Anything this old is going to have worn and uneven running surfaces.

[Charles 230SL]

thanks Benz Dr., your comment: "If you have good oil pressure this end play may not be as big of a problem as it seems".

Since it has good oil pressure, whats the worst that could happen if I just let it go? When the crank pulls forward, does it settle in one (forward) position and remain there while running? Note that its a standard shift.
thanks, Charles

[ja17]

Yes I would hesitate to jump into this job also.  Dan has some good points. A drop in oil pressure should give you notice of when things start getting critical.

[Benz Dr.]

The crank will tend to pulll forward and stay there while running. Oil pressure should be full when cold and may drop down to 15 PSI at idle. This is OK as long as you have full oil pressure by 1,500 RPMs.  Any drop from full pressure on the gage at road speeds is a sign of excessive bearing wear.
I always use a new oil pump on a full rebuild.  An oil pump will last up to 150,000 miles but not 200,000 miles with the kind of oils that were used during the 60's.  Oils are better today but the curent drop in zinc levels is troubling for flat tappet engines, which is what we have.  Heavy cam shaft and ball stud wear can result by using the wrong type of oil.

Keep an eye on it and sart saving for a flull rebuild a few years from now.

[Charles 230SL]

got it,, thanks Dan

[tel76]

What are the tolerance's for the crankshaft end float in the BBB, 004 thou does not seem excessive to me ?
Please confirm that you mean end float in the crankshaft.
It would be a good idea to place a dial gauge on the front of the crankshaft and determine the actual figure,

[ja17]

Yes, .004 " is correct. If it is quite noticeable,  I suspect Charles is looking at about 3/32" or (.091"). This would be twenty times the specified dimension.

[Charles 230SL]

yes, I'd estimate lateral movement is at least .091".
There's currently 51,300 miles on the odometer (which I presume is actually 151,300). But even with 151K miles, the main/thrust bearing wear still seems excessive to me. I wish I had some history on this car - I bought it at auction about 2 yrs ago.

take care all, Charles

[Benz Dr.]

I thought maybe you were looking at a small amount of play.
.090'' is a lot. I would be thinking about fixing it before it fixes you. 

[paul_GB]

.. to pick up on this older thread. I am just installing replacement main and rod bearings in my 230. The crankshaft journals are in good shape and required no machining. All the replacement bearings have gone in fine with the exception of the thrust bearing on the second journal (from the engine front). The new thrust bearing shells (outer width) are too wide and foul on the crank journal shoulders.  Dr Benz mentioned 'sanding down' the rearward thrust bearing surface to get a fit and achieve correct end float. All seems very logical!! What is a good method to do this without screwing up and ruining the bearing?? Recognising this is a precision process. Any pointers from folks who've done this before gratefully received.. I've come this far and don't want to mess up now. I have basic garage tools available.. incl a sander (if required). Thanks... 

Paul

[paul_GB]

.. sorry I think I read Dr Benz earlier thread incorrectly. With a re-read I gather it's actually the thrust bearing end surface that is foremost (facing the front of the engine) that is best sanded or ground back. Hence the rearward thrust bearing face remains true and snug against the journal shoulder face as the crank pulls forward. I should pay more attention  . I don't have a bench grinder.. wondering if now is a good time to buy a decent one for this job???

[Benz Dr.]

I had my machinist do this on his crank shaft grinder that had a very large stone on it. He held the bearing lightly against the side surface of the stone and checked it after each hit until it fit. He warned me against using a belt sander claiming it would easily sand right past and through the amount desired.

I've used a mill file to remove most of what I want and then I use a heavy piece of glass with a sticky sanding disc laid on top of it. The glass will keep the bearing surface flat and what I do is swirl the bearing around in a somewhat circular motion which will remove all of the high spots. This will give you a surprisingly flat and true surface. Careful measuring is essential for a good outcome. Measure the thickness at each end of the bearing to make sure they stay even as well as the top and bottom sides of the bearing so that everything stays in line.

This won't be 100% perfect but if done carefully it will still give good results and it should be fine. Yes, file the front facing side of the bearing so that the true original surface runs against the crank on the side you didn't touch.     

[tel76]

Paul,
Have you compared the thickness of your old ones with the new, are the new ones correct or did you purchase o/s thrust bearings for some reason?
If the crankshaft has not been reground on the thrust faces then standard ones should not require any work.
Have another look before you start modifying.

[paul_GB]

Thanks gents. Using a hand grindstone I've honed the one side of the thrust bearings and the are now a snug fit around the crankshaft journal. The original ones measure about 30.2mm wide.. The replacements (out of the box) were 30.5mm. I didn't need to remove much metal. With my new bearings installed there is very little discernible end float. Is there a minimum measurement for crank end float?

There are two straight grooves cut in the outer thrust surfaces of the bearings.. about 6mm wide and 1mm deep. Assume these encourage oil flow onto the journal shoulder/ thrust surface. Should I recut these to the 1mm depth on the thrust face that I've ground back?

I was only aware of different thrust bearing diameter sizes, not widths.. have I missed something here?  . A plug and play set would have been ideal. Note I have replaced with the same diameter bearings as those I've removed (first repair, 0.25).

Sorry measurements in metric!

Paul

[Charles 230SL]

Paul,
engine specs (attached) show crankshaft endplay as .004 - .007 (.10 - .17 mm) but they don't identify a minimum endplay.  Since too little clearance could result in excessive bearing temperature rise and reduce rate of oil flow on the journal shoulder, I'm not so sure I would want to go any tighter than .004 (or even .003) on the thrust clearance. 

[paul_GB]

Much appreciated Charles. Thanks for pointing the heat/oil issue out, I best hone a tad more of the thrust surface to ensure I get the 0.1mm.
I am just awaiting delivery of the crank rear oil seal then I can begin the process of closing up the sump etc.
I'll say it again.. the help from the community on this site is invaluable... 

Paul

[stickandrudderman]

It's because of this that I only grind a crank once I have the new bearings to hand.

[paul_GB]

Stick.. I haven't reground the crank, my local mech workshop checked it over and said it didn't need it. I didn't want to regrind unless absolutely necessary, especially the crank thrust surfaces. Cheers.