Main bearing taper..

[64PI]

Checking main bearing clearance last night and I have a couple bearings with some pretty healthy taper. The block has been align honed and and I'm checking clearances using a bore gauge. Even when I move the bearing halves to a different cap/saddle I'm still seeing about .0005" of taper. This is using a 125M10 bearing. It's not all bearings only 2 sets out of 5. When I was putting together an engine last year I seem to recall the same issue with the 125M. I had to use Cleveland bearings to get clearance then and it solved the taper issue also. I need to gain a little clearance on this one but I cant seem to find .011" Cleveland bearings. The mains without taper are .0018-.002.. The mains with taper are .002-.0025 and .0025-.003. The crank is a fresh grind and checks out within .0002" across all 5. I haven't Mic'd the bearings yet. Is anyone else seeing this with FM bearings? I hope its not just me!


Fred

[blykins]

I have seen it quite a few times recently. 

Try dressing the lettering on the backs of the bearings.  If that doesn’t work you may need to polish some clearance into the crank and switch to a different bearing. 

[My427stang]

Brent has a very good idea, I haven't tried it, but absolutely worth a shot.  Heard a lot about a little dressing of the bottom of bearings on the outside, but never did it.  Likely could work for the slightly tight ones too

I am not an FM hater, but I am drifting away.  I like the main bearing design, but have gone full groove mains on the last 3 on the mains because I couldn't get the numbers I want, and I have pretty much given up on FM rod bearings and gone Clevite.  I have seen the FM mains and rods loose, tapered, and not the same as each other.

I would measure your main bore and make sure there is no taper and if it's in the bearing, I'd probably consider a set from a different brand as an experiment, even if it was a cheapo set you could sacrifice if you decide to polish and fit if things are repeatable. 

I hate to admit it, but on my own temporary F100 engine, a 390 bench build (as in all the parts laying around under the bench) build I used Enginetech...squirmed when I took them out of the box, a real odd bearing, aluminum shell, but all the numbers came in spot on and it didn't miss a beat

FWIW, I have 2 sets of FM rod bearings I keep trying to use, over a few builds now, they always come up loose, one set had a chunk of something embedded in it.  Bought a set of narrowed Clevite, and it's like a production shop assembling the rods.  Once I got a combo for one rod, every other one was the same. 

[64PI]

I'll order up a set of Clevite full grooves to have on hand... just in case. I was looking at King bearings but I wouldn't have them for a few weeks. I will try dressing the bearings tonight to see if that helps any. I have a set of .030 under Muskegon main bearings new in box a guy gave me.. Pretty sure they are older than me. Just need to find a home for them.

[64PI]

FWIW, I have 2 sets of FM rod bearings I keep trying to use, over a few builds now, they always come up loose, one set had a chunk of something embedded in it.  Bought a set of narrowed Clevite, and it's like a production shop assembling the rods.  Once I got a combo for one rod, every other one was the same.

You weren't kidding about the rod bearings. Mic'd my crank up and it came in around 2.4280.. Gave me .0035-.0037" clearance. I even checked the clearance using another set of rods and had the same results. So for grins I threw in the .030" under Muskegon bearings and checked them at 2.4080" and got .0025-.0027"..

I have Clevite Rod and mains on the way. I messed around with the mains tonight and still am not happy. Tried dressing up some of the halves and swapping them around. The upper halves were pretty consistent, maybe .0002" off from the front to back of the shell. The bottoms were another story with .0005-.0008" front to back. Checked the main bores and the are dead true.

 It's too bad we cant find a better source for more consistent bearings. Maybe I will take take the FM bearings to work and strip the coating off and see if I can plate them and hold a tighter tolerance. I used to work with a guy who raced carts back in the 70's. He said they used to take the cages for the crank bearings and silver plate them.. I wonder what they coat race bearings with..

Fred

[RustyCrankshaft]

I hate to admit it, but on my own temporary F100 engine, a 390 bench build (as in all the parts laying around under the bench) build I used Enginetech...squirmed when I took them out of the box, a real odd bearing, aluminum shell, but all the numbers came in spot on and it didn't miss a beat

Not all, but most of the Enginetech bearings are actually King bearings in a different box. A lot of times with a different part number, but they'll have the King logo stamped in the back side of the shell.

Not on real high performance stuff usually, but in stock-ish applications I've used a ton of King bearings because....I get a really good deal from Enginetech and they are a sister company to Competition Products and can order stuff between warehouses and for 98% of the stuff I ever do they've been pretty good to me and consistent from lot to lot. Haven't checked recently, but found out the hard way they don't offer a small diameter thrust bearing even when you spec a early model year.

I've also used King on a few aircraft engines now as well with good results.

[Barry_R]

You weren't kidding about the rod bearings. Mic'd my crank up and it came in around 2.4280.. Gave me .0035-.0037" clearance. I even checked the clearance using another set of rods and had the same results. So for grins I threw in the .030" under Muskegon bearings and checked them at 2.4080" and got .0025-.0027"..

 It's too bad we cant find a better source for more consistent bearings. Maybe I will take take the FM bearings to work and strip the coating off and see if I can plate them and hold a tighter tolerance. I used to work with a guy who raced carts back in the 70's. He said they used to take the cages for the crank bearings and silver plate them.. I wonder what they coat race bearings with..

Fred


You have a defective set of bearings.  They would probably take them back and trade for another set, but the cost and PITA often does not justify it.  I have sent some back in the past - figured they could not fix a problem they did not know about.  They are not silver plated -at least not in the traditional dip process sense.  The tin overplate on a traditional passenger car bearing is not used on a race bearing.  The lining on the bearing is something of a copper/lead/tin witch's brew that is applied to the flat strip as a powder and then cooked.  There were some pre and post lining dips in various evil potions, but they were for adhesion and cleaning purposes.

[My427stang]

Barry, do you have a contact at FM?  I buy through distributors, but I'd take the time to send them the the rod set with a big chunk in it to let them see.  I contacted them through their main corporate web site, but no reply

It's a set of coated, so worth the effort for another pair, but I will also say as said before, not sure what happened, but the measurements are all over the place.  .001 bearing pair gets me .0005 at best, and sometimes even nothing.  Clevite has been spot on.  This is all in the past 18 months or so.

[Barry_R]

After a few rounds of reorganizations and buyouts, the F-M I worked for no longer exists...I don't think I know a single person there anymore

[blykins]

I've been having consistency issues with them as well, to the point where I've started to shy away from using them.  Their 125M series has given me all kinds of taper grief, as well as being way loose on clearance. 

[Falcon67]

>I cant seem to find .011" Cleveland bearings.

They don't exist AFAIK.  I need some both main and rod, no go.  Custom order AFAIK.  There used to be .001 over bearings but those were discontinued long ago.  Did see a set on eBay about a year ago.

[64PI]

The Clevites I ordered are not much better size wise.. No taper at all. The bearings are a lot thicker than the FM and put the rod and mains  way too tight.  I got rod clearance by mixing the FM and Clevite shells and ended up right at .0025". The crank is  going back to get half a thou dusted off the mains. I'm hoping I can swap the tapered FM shells with the Clevites and between the two end up with .0025 ish on the mains. With a crank that's ground to low limit I didn't think I'd have this much of a struggle getting clearance.