A fix for .015 O.D. main bearings
Posted: Sun Jan 17, 2010 7:12 pm
If any of you have ever had to rebuild a block that has been lined bored to .015 oversize O.D. main bearings you will have little choices for repair, and the norm is to get a replacement block because oversize O.D. bearings are harder to find than hens teeth. (Do not confuse these with the normal undersize bearings used when regrinding crankshafts down .010, .020, etc.)
I doubt I’m the first person to do this and this fix is probably not for everyone, especially if you plan on taking it out in the field and really working it. For me the block would have been useless as is and hopefully the only other thing to get wrecked if the fix were to fail is the crank, not a good thing to wreck but not the end of the world ether. My concern is having the shims work their way out from underneath the bearings, especially with the forces seen inside of a diesel, hopefully using loctite to hold them in place is the answer, at this point I only have about 20 hrs on the engine but I did plow under a acre or better with it this fall and have had no issues with it yet.
I cut shims from .007 shim stock and punched holes for the oil passages and for the locking tabs on the bearings, nipping the end open on this hole to make a slot.
Rolling the shims to the correct circumference helps drastically.
I used Loctite RC 680, it has an extremely high shear strength and is good to over 300 deg F. everything has to be CLEAN, even the natural oils in your hands can be a contaminate. I applied the Loctite to the shim and installed in the cap and the block, then applied the loctite to the bearing and installed them making sure all shims and inserts are squarely in place, with the end of the insert having the locking tab slightly proud of the surface insuring that it will be set properly when assembled.
I then used a combination of poly and hose to make a fixture to hold everything in place until the Loctite set, the idea here was to bolt the cap down in place while having the bearing clamp down on the fixture hard enough to seat the bearing/shim assembly but not so tight as to force all the loctite out. I did one set a day giving each one ample time to set before going on to the next one.
UPDATE
It’s been well over two years now and the bearings have worked great! Unfortunately I had to tear the engine down because of an oil issue with the cam/valve system, while doing this I found a problem that I had overlooked during the original assembly, too much loctite! I used so much that it had settled into the bottom of the oil passages under the crank, set, and blocked off the passages, luckily the oil could still get through by taking the “long way around”. During this last reassembly I applied the loctite with a Qtip, and worked quite well.
Pat
I doubt I’m the first person to do this and this fix is probably not for everyone, especially if you plan on taking it out in the field and really working it. For me the block would have been useless as is and hopefully the only other thing to get wrecked if the fix were to fail is the crank, not a good thing to wreck but not the end of the world ether. My concern is having the shims work their way out from underneath the bearings, especially with the forces seen inside of a diesel, hopefully using loctite to hold them in place is the answer, at this point I only have about 20 hrs on the engine but I did plow under a acre or better with it this fall and have had no issues with it yet.
I cut shims from .007 shim stock and punched holes for the oil passages and for the locking tabs on the bearings, nipping the end open on this hole to make a slot.
Rolling the shims to the correct circumference helps drastically.
I used Loctite RC 680, it has an extremely high shear strength and is good to over 300 deg F. everything has to be CLEAN, even the natural oils in your hands can be a contaminate. I applied the Loctite to the shim and installed in the cap and the block, then applied the loctite to the bearing and installed them making sure all shims and inserts are squarely in place, with the end of the insert having the locking tab slightly proud of the surface insuring that it will be set properly when assembled.
I then used a combination of poly and hose to make a fixture to hold everything in place until the Loctite set, the idea here was to bolt the cap down in place while having the bearing clamp down on the fixture hard enough to seat the bearing/shim assembly but not so tight as to force all the loctite out. I did one set a day giving each one ample time to set before going on to the next one.
UPDATE
It’s been well over two years now and the bearings have worked great! Unfortunately I had to tear the engine down because of an oil issue with the cam/valve system, while doing this I found a problem that I had overlooked during the original assembly, too much loctite! I used so much that it had settled into the bottom of the oil passages under the crank, set, and blocked off the passages, luckily the oil could still get through by taking the “long way around”. During this last reassembly I applied the loctite with a Qtip, and worked quite well.
Pat
One thing I may have attemted myself would have been to mill a little off of the main caps and then shimed it the same amount milled off with a spacer to capture the bearings and keep them from spinning like a lot of early engines that were made with poured babbit. You also would have had to take a little off of the cap bearing ends so that the shim would have locked it. Then it would have been positivly locked in.