semi finish bearings / resizeable bearings / full floater
 

Hello Guys,

since i have a rod bearing damage and figured out my crank was allready grinded 0,030 under i bought a set of semi finish full floater bearings / resizeable bearings. Has anbody of you anytime cut / bored those bearings to size and can give me advice how to get them fit?

thanks all

Ingo

Re: semi finish bearings / resizeable bearings / full floater
 

Look up Walt on here, pretty sure he's had a lot of experience with these semi finished bearings.
Martin.

Re: semi finish bearings / resizeable bearings / full floater
 

ha thats funny, Walt was it who recommend to post my question here in the barn. As i understand him he used those bearings back in the 60s but he gave it to a machineshop to cut them to size. So he personally doesn´t know how to do it...

Re: semi finish bearings / resizeable bearings / full floater
 

Semi finished just means the bearing is maximum undersize with a bearing material thicknes enough to resize it to less undersize.
On a fixed bearing its just to install it in a rod and hone.
On a full floater you need a fixture to hold it tight making sure its round before sizing.

Re: semi finish bearings / resizeable bearings / full floater
 

Thats it! I considered to bore a sleeve on my lathe, put the bearing in the sleeve (as tight as possible) and then bore the bearing to the needed size. I just wonder if anyone has some special advise ...

Re: semi finish bearings / resizeable bearings / full floater
 

You got it pretty right INGO. I cut many many semi bearings back in the 60-70, My brother use to turn cranks and also with portable crank grinder. A lot of trucks would spin a rod bearing and bro would grind journal in the truck, he would call be back in the shop and I would cut a semi bearing to size. Also ground many semi pistons. Those jobs are about all gone now. It would pretty hard now to find a shop that has any of those machines. Simple things like knulling pistons and installing spacers in worn top ring groove. The younger generation are missing all that fun stuff. Walt

Re: semi finish bearings / resizeable bearings / full floater
 

Look up Tobin Arp bearing resizer on Google and you will see the way it is done.

Re: semi finish bearings / resizeable bearings / full floater
 

The Tobin machine is essentially a 'line bore machine' for bearing shells and/or caps. If you can find somebody who has one and knows how to use it, then this would be a good approach. I believe you could make a one-off custom holder that would work in a lathe - specifically for the full-floater 91A/21A bearings you have. If you want me to draw you up a 'fixture' - and then you could have it made, ping me off line. There are guys with the Tobin machines - you should be able to just send them your bearings and the crankshaft dimensions . . . if you can find "that guy". Good luck

Re: semi finish bearings / resizeable bearings / full floater
 

Making a fixture for the floaters, getting machine work done etc. seems to me would cost a whole lot more then just getting a good crank that is ground to the size of the good throws and getting 1 pair of new shells for throw that was damaged. Or even having the 1 throw welded up and ground back to the size of the rest.

Re: semi finish bearings / resizeable bearings / full floater
 

Yes, I have some suggestions after having performed this operation several times---the OD of the bearing shell should be clamped such that it is perfectly round and matches the diameter desired to fit the rod housing. Just boring a sleeve to be a tight fit on 2 bearing shells will not do it correctly as the gap between the 2 shells will likely cause the sleeve bore to differ from the rod housing and getting the bearing shells to perfectly conform to the sleeve bore will be a challenge. But, if the shells are not tight in the sleeve, all around the outer perimeter, the shells will have thick-thin conditions when re-bored.

I did one set in a lathe where I tapped the oil holes and screwed the shells to a bored sleeve. My results were just "ok".

Your results might vary.

Re: semi finish bearings / resizeable bearings / full floater
 

JWL has a good point. Maybe a good approach would be to create the fixture and then use some .001 or so shim stock all around the outside of the bearing - to simulate oil and clearance. I'm just talking out loud. If it was me, I'd find a replacement 59x or 8BA crankshaft and not screw with it (but he already knows that part from me! LOL)

Re: semi finish bearings / resizeable bearings / full floater
 

Tanks guys for your tips, i´ll try and Keep you posted

Ingo

Re: semi finish bearings / resizeable bearings / full floater
 

What year engine are you working on? I have a pair of flanged .040 under bearings I don't need.

Re: semi finish bearings / resizeable bearings / full floater
 

I dug out this Sunnen bearing sizer, it has a proper sized insert holder, I have the instructions, a few pieces of tooling are missing but not hard to make, it was all stuck not moving with congealed oil I got it freed up some but it needs to be taken apart to free up the feed

Re: semi finish bearings / resizeable bearings / full floater
 

The phone only loads one picture

It uses the sunnen machine to adjust the cutter, looks to be somewhat trial--error to get size, the instructions say to take a cut and measure, each graduation on the machine dial is about .001----seems like it would take some practice to be consistant---it does look like the insert can be removed without changing the setup so once the inserts were close the final cut could be repeated by just changing the insert, no change in cutter depth

Re: semi finish bearings / resizeable bearings / full floater
 

Thats a nice little attachement.
Big i want one factor...another one to the list of stuff to find.

Re: semi finish bearings / resizeable bearings / full floater
 

sorry i wasn´t there a couple days. I have a 39-42 engine without flanges bearings.

Thank you

Ingo

Re: semi finish bearings / resizeable bearings / full floater
 

Dale, i would be glad when you draw it for me.

Thank you

Ingo

Re: semi finish bearings / resizeable bearings / full floater
 

Okay Ingo - I'm working in CAD this evening, will send it your way . . . both the 3D CAD model as well as a 2D drawing.

Re: semi finish bearings / resizeable bearings / full floater
 

Here is a screenshot of the bearing holder - designed it in SolidWorks. I'd make it out of 6061 Aluminum. It needs to be dead-nuts correct in the inner bore - so the bearings sort of 'press in' by hand. The depth of the pocket leaves about .005 of the bearing sticking out - so the top plate can be used to hold them down and in position.

I made four 'relief' holes (1/2") that go all the way through the main part - so that one can use a wooden dowel rod or something soft in case they need to "tap" the bearings back out after the machine operations (from behind). I usually forget crap like this - than wish that I didn't!

Can't say that I've ever attempted to 'bore bearings' on a lathe, but there is no reason it can't work if the machine is good and the operator knows how to do precision work.

If anybody wants a copy of the CAD model, just ping me . . . not a big deal by any means. :)

B&S

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