Slop in thrust bearing

[Steve C.]

I just recently found out that the '72-400 block for a new engine build-up has problems with thrust bearing fit. On both sides of the webbing it is scored so that when you fit the bearing down in place there is excess slop. It will move for & aft a total of about .006". It seems the bearing fit on the cap side is ok. For the most part the block work is done and ready for assembly. The work includes sonic testing, welded-in lifter bore braces, filled block, installation of 4-bolt steel caps w/ studs, align bored & honed cylinders bored & honed w/torque plateand the deck surfaced. This will be a 7000 plus rpm application with LOTS of torque and a 4200 stall converter. We discovered this situation when we went to test fit the crankshaft. Unfortunatly the crank was made incorrectly by Crower and it has to be returned for a dimension change
(the rope seal area was made to big), so the crank won't drop in and therefore we don't know what the final fit will be like with the other bearing half in place and the cap installed. Needless to say I'm worried about the integrity of this engine. Your input and suggestions will be greatly appreciated. If futher input is needed please ask and I will do my best to furnish the information. Thanks.

[Steve C.]

I just recently found out that the '72-400 block for a new engine build-up has problems with thrust bearing fit. On both sides of the webbing it is scored so that when you fit the bearing down in place there is excess slop. It will move for & aft a total of about .006". It seems the bearing fit on the cap side is ok. For the most part the block work is done and ready for assembly. The work includes sonic testing, welded-in lifter bore braces, filled block, installation of 4-bolt steel caps w/ studs, align bored & honed cylinders bored & honed w/torque plateand the deck surfaced. This will be a 7000 plus rpm application with LOTS of torque and a 4200 stall converter. We discovered this situation when we went to test fit the crankshaft. Unfortunatly the crank was made incorrectly by Crower and it has to be returned for a dimension change
(the rope seal area was made to big), so the crank won't drop in and therefore we don't know what the final fit will be like with the other bearing half in place and the cap installed. Needless to say I'm worried about the integrity of this engine. Your input and suggestions will be greatly appreciated. If futher input is needed please ask and I will do my best to furnish the information. Thanks.

[Dick Duclow]

Is the .006 "slop" all to the front, the rear or evenly split?

[Steve C.]

Dick, When we set the bearing down into place and then put a dial indicator against the side (lip ?) of it. It will move about .006" on that one side.

[Gach]

Steve it's possible to shim the thrust bearing to get rid of the slop, and I don't think it would be a problem down the road, but the other problem you mention I don't think is fixable. There has to be a slot for the bearing tang in oder to hold the bearing, and keep it from moving. If you can't put a slot in that area, then I think you have a problem, and from the sounds of what your saying I don't think that's possible

[Steve C.]

I was asked if I varified that it is not the thrust bearing itself that is out of spec. Good point and I will address that with my machinist on Monday. The other bearings seem to be ok (un-related to this and nothing to do with fit, but there is poroisty in the rear main bearing surface in the block- another thing to deal with). FYI the bearings are Federal Mogul Competition Series (3/4 groove)/ main bearing set #113M. I have not heard of any fit problems with these, maybe someone else has.

[Vascar]

I'm not sure but I think the competition series main bearings are not only harder but also on the lower side of the specs. I don't know if I said it right, But if the standard bearing is 2.988 (these are not actual sizes)the competition series might be 2.986.. They are thinner by a tiny bit. Now I'm not sure if they do that to the thrust surface too.
I was looking for a bearing that would of given me tighter clearances on my 455 and the comp series wasn't even an option because of their out of box sizes.

[This message has been edited by Vascar (edited 01-09-2000).]

[Steve C.]

I spoke with my machinist this morning. He tried two other thrust bearings... they too are loose. For the record they are ok on the cap. Ok fellas, where do I go from here.... any input and/or suggestions regarding this situation. Any engine builders out there ?

[Vascar]

Maybe you might have to get the thrust surface welded up.
What a knuckle head I am!!! It's your block and not the crank... Sorry bout that. This flu really got to me. You might want to check the block for cracks in the web area too.

[This message has been edited by Vascar (edited 01-10-2000).]

[Triggerman]

Steve, you could have the thrust surface on the block welded up and then re-machined to the proper spec. However, the heat might effect some of the other block dimensions. Most every block dimension would have to be verified afterwards. Also could machine down both sides to arrive at a thickness which could be shimmed with shim stock. I would want the shim stock to be completely captured by the surfaces of the thrust bearing in order to make sure it could not vibrate out. I don't think I would run it as is currently is. You are correct about reducing the bearing surface area by half will result in the thrust force being effectively doubled (if the cap side of the bearing has to take all the load).

[Paul Spotts]

The problem may not be a 72 400 but that particular block. It may have been the usage of this block. It sounds like the thrust bearing may have spun causing the scoring - but I didn't think that was possible. The bearing fits the new main cap - but do you have the old cap to see that fit? I had a thrust bearing go out from my block and it was found out later that it was trans related. The manual valve body i was running apparently caused excessive fluid pressure pushing the converter into the the flex plate. Manual trans cars with stiff or high pressure clutch pressure plates also can wipe a thrust bearing. For a 7000 RPM motor I would not suggest shimming - a good idea but has anyone done this? I would find a better block - sounds like it will come back and haunt you. I'm not thrilled with welded in lifter braces as I have heard of problems from other racers - yet there are talanted guys out there welding cast iron. There are two bolt in type braces made as well. I know you have some bucks in that block - I feel for you I would just be nervous in any kind of "fix".

[This message has been edited by Paul Spotts (edited 01-10-2000).]

[GTO]

I have the same problem with my 455 block but I only realized it was a problem by reading your post! I tore my motor down after 1 season and checked the bearings. Mine was also loose on the block and not in the steel caps. I figured that it was OK because an engine shop put the short block together for me as a package deal. My block is a 1970. After aprox. 500 street miles and about 50 runs at the track (with 200HP NOS) going 10.21@132 I saw no wear on the thrust surface , crank or block. I will take a closer look now and take some measurments. I'll let you know!...ERIC V.

[Steve C.]

Unfortunatly I do not know the history of this piticular block and the origional caps are unavialble. It came from the inventory of blocks on hand at the shop that did the pliminary work. They selected the block, sonic checked it, filled it, welded-in the lifter bore braces, installed the steel caps and then had it align bored & align honed. After this work the block was then shipped by truck to my machinest here in Austin for the balance of the work and assembly. It is our opinion that it was a previous spun thrust bearing that caused the damage. Also as I mentioned, and un-related to this thrust bearing situation, the block also has poroisty on the rear main bearing surface area.

[Steve C.]

Thanks for the comments and suggestions. In a un-related discussion I read the following, it was said "In the world of high Performance, we must relize that anything can go wrong, and not have to make sense-or have a person to blame". Everyone involved has been very cooperative and willing to work together to solve the problem... which appears may not be as bad as I "feel" it is ( after 2 years on this project I'm frustrated! ). Our next step is to wait for the crank to get back and then we will set everything up and review the stiuation and go from there.

[Michael Farich]

Just a thought - a stripe of bearing mount (loctite or some similar type stuff) could be applied to the side of the main bearing saddle to support the thrust faces. I know normally this is bad as it would be a thermal barrier but it might be OK if only used under the thrust face. I think bearing mount is good for 0.015" or so. Read up on it first to make sure in case I'm mistaken.