Thrust cap alignment varies

ThikStik

My sleep apnea is winning
Joined
Mar 27, 2002
Hey guys, Im doing a rebuild of the 1987 3.8 below using HRParts' 2 and 3 billet caps and main studs. After getting block back from mach shop i notice that when torking the thrust bearing down its alignment is off. The 2 halves dont overlap exactly. I remove and try again-now its off in a different way!
There is a positive tightness when the cap meets the last few millimeters of the block sides, so this seems weird. I am aware of a rebuilder's trick of banging the crank from behind to center up the thrust bearing halves , but is this the way of a "true TR craftsman"?! Thanks
 
We do lots of steel caps including Chevies and the procedures are basically the same. If the cap is not properly fitted in the block, it will walk and destroy bearings, crank and possibly the block too.

In process now is a 3.8 with caps that was done by another shop and only run at the Buick event in Las Vegas for a few runs. Caps walked and already ruined the thrust bearing. There are many shops that can do this properly but it consumes lots of machine time and labor, therefore, it is not cheap to have it done right. It is VERY expensive when NOT done right.

Gene, do not mean to "bash" you, just add some info. Procedures are not the problem between different motors, it is the care and attention to details in general. Yes, Chevy or other brands have different tolerances and specs so this must be considered when machining and assembling an engine.:)
 
Originally posted by Nick Micale
We do lots of steel caps including Chevies and the procedures are basically the same. If the cap is not properly fitted in the block, it will walk and destroy bearings, crank and possibly the block too.

In process now is a 3.8 with caps that was done by another shop and only run at the Buick event in Las Vegas for a few runs. Caps walked and already ruined the thrust bearing. There are many shops that can do this properly but it consumes lots of machine time and labor, therefore, it is not cheap to have it done right. It is VERY expensive when NOT done right.

Gene, do not mean to "bash" you, just add some info. Procedures are not the problem between different motors, it is the care and attention to details in general. Yes, Chevy or other brands have different tolerances and specs so this must be considered when machining and assembling an engine.:)


I've lived this nightmare . Purchased a block off of a local list member with 3 billet caps . he had to take it to another shop after the first shop screwed up the align bore and caps. then I purchased it from him. the thrust does not last more than 5 mins on intial start up . has happened twice ,billet thrust cap has been replaced and block realigned bored again ( 3rd time ). I still do not know it is 100% good . crank endply sets in at .008" , after 5 mins of run time in park endplay ends up a .011-.012"" and a pan full of bearing material .had TC opened up and inspected it checked out 100% . take it from me you do not want to go thru this .
 
I'm trying to sort out thrust bearing problems myself. All I did was freshen a stock shortblock and wiped the thrust bearing after 4000 miles. Installed new main bearings with the engine in the car and wiped them in 1000 miles. As with the first time, blew all the bearing material off the bottom shell of the thrust bearing. Put another set in but drilled out and chamfered the oiling holes in the bearings to 1/4" and filed the edge of the bearing shell as illustrated in that article above. I have another 4000 miles on them but I'm not sure it's OK. I'm going to drop my pan pretty soon and take a look. :skeered: ;)
 
Thanks John for article-that backs up the technique of loading the crank in order to align the thrust bearing. And, I DO recall criss crossing marks on crank surface.
Nick, can you give specifics on what machine shop should and should not do? As mentioned, there is not slack between new cap and block side bosses, but it is just that the cap can be "walked" down in any haphazard configuration and stay that way after a final torking. SCARY. It just seems like there should be a self centering component there, especially upon final tork down. This machine shop has been a shop of horrors so far. banging my crank after it had been polished, then charging me for turning it to .o1o. And missing the excessive piston pin clearance. I guess i got to go to 030 now due to no oversize pins being availoable.
It never ends! Next time i will use only vendors on this board for machine stuff. Cheaper to ship engine than deal with errors!:
 
Here's some more thrust bearing info I got off the board.....Maybe there is something more that will help out.

.Automotive Engineers Rebuilders Association - Crankshaft Thrust Bearing Failures

Crankshaft Thrust Bearing Failures
Crankshaft thrust bearing failure on vehicles equipped with automatic transmissions have mystified the engine and transmission rebuilding industries for quite some time. AERA has attempted to address these failures with technical bulletins as early as 1981. AERA bulletin numbers TB 229, TB 284 and TB 336 have all discussed these failures from different viewpoints.
Greg Boehm of Valley Transmission in El Cajon, CA with the assistance of Ed Hale have documented results of their investigation into the causes of crankshaft thrust bearing failures. AERA would like to extend its thanks to them for sharing their findings with us.
Early AERA bulletins attempt to relate the failure of crankshaft thrust bearings with the torque converter, but replacement of the torque converter does not always solve the problem. Similarly, replacement of the complete transmission or the crankshaft and bearings does not always solve the problem either.
Using a device that incorporated a port-a-power with a pressure gauge and a throw-out bearing, tests were performed on a V8 engine with a failed thrustbearing and a THM 350 General Motors transmission. It was determined that excessive forward pressure was being placed on the thrust bearing (150 to 300lbs.). After disconnecting the torque converter, the pressure dropped to zeroand the crankshaft would run wherever positioned by the fixture with no forward pressure registering on the gauge.
Replacement of the torque converter, stator support, and input shaft did not reduce the forward pressure exerted on the crankshaft. Other areas of the transmission were checked, replaced or modified in an attempt to reduce the forward pressure on the crankshaft to no avail.
Pressure gauges were finally hooked up to the transmission cooler lines. The transmission output line (converter fill) had 100 lbs. Of pressure while the return line (lube oil) only had 10 lbs. This indicated a restriction in the cooler or lines to the cooler. Bypassing the cooler substantially reduced the forward pressure on the crankshaft. Further tests indicated a positive relationship between lube oil/converter pressure and forward pressure on the crankshaft. Reducing the lube oil/converter pressure to 30 lbs. At full throttle reduced forward pressure on the crankshaft to nearly zero.
It is believed that excessive lube oil/converter pressure builds up between the front pump and the hub of the converter creating excessive forward pressure on the crankshaft. The bypass valve generally cannot vent this excessive pressure.
The AERA Technical Committee advises the following steps be taken when thrustbearing failure occurs:
1. Attach pressure gauges to the cooler lines to compare inlet and outlet pressures. They should be very close to the same reading and be in the 20 to 30 lb. Range.
2. If the cooler inlet pressure is substantially higher than the outlet pressure, investigate for any restrictions in the lines or the cooler.
3. If the line pressure is within specifications, the transmission should be checked for spline wear on the input shaft which may be causing bind and not allowing the converter to properly move rearward on the input shaft. Other areas of the transmission should be checked that directly contribute to relieving pressures and/or building excessive pressures.

In addition to the mechanical items above that can be corrected, the vehicle owner should be advised to avoid lugging the engine in high gear, and to avoid prolonged climbing of hills in high gear especially with heavy vehicles or whiletowing trailers, other vehicles, etc. Working the engine and transmission hard in high gear dramatically raises the lube oil temperature which can lead totransmission failures that may increase pressures on the converter. It is best to manually shift the transmission into a lower gear to decrease wear and tear on the transmission.

Technical Bulletin Number TB608
December 1989
Automotive Engineers Rebuilders Association - Crankshaft Thrust Bearing Failure W/Manual Transmissions

Crankshaft Thrust Bearing Failure With Manual Transmissions
AERA members have reported several instances of premature crankshaft thrust bearing failures on vehicles equipped with manual transmissions. At times this symptom is followed by low oil pressure complaints or complete main and rodbearing failure.
Inspection of the affected engine should be completed before the engine is removed from the vehicle. Check for proper clutch pedal clearance. An improperly adjusted clutch with insufficient free play will cause excessive pressure against the crankshaft thrust bearing.
Check for misalignment of the pilot bushing or bearing and pilot shaft. Improper alignment may prevent the bell housing from engaging properly with the cylinder block. The transmission bell housing should mate to the cylinder block freely. If it is required to draw the bell housing to the cylinder block using bolts,chances are a misalignment has occurred. Again, misalignment of these components will cause excessive thrust pressure against the crankshaft thrust bearing, resulting in premature failure.
Failure can also be the result of an off-center bell housing. Check the housing run-out with a dial indicator. Correct any run-out error according to manufacturer's recommendations.
Whenever you are investigating premature crankshaft thrust bearing failures, it is important to verify the movement of the crankshaft by using a pry bar or other suitable tool. If an alignment problem exists, there should be some resistance when moving the crankshaft toward the transmission. When pry bar pressure is removed the crankshaft will most likely come to rest as far forward, away from the transmission, as possible. After the excessive pressure is removed and/or the misalignment corrected, the crankshaft should be able to be moved easily in either direction
 
WOW

we have had this problem MORE THAN ONCE....I dont understand why program industries cant machine a damn main cap squarely.....unbelievable!!!!

actually had a buds motor going together last night and the cap was WAAAAY too loose, time for welding and re-linehone....:mad: :mad: :mad: I'm going to start making the damn caps myself:cool: :cool: :cool:
 
So Keith, you are basically saying that cap should self align on tork down? If not, then what is built up/welded-cap or block? I do notice that cap's edges are rounded where they meet at block edges. Maybe this is done so as to not crack the square area (boss) that cap sits against.
. I imagine it is more squalid aftermarket part issues-Ahh, consistancy!
Has anyone tried dowels? Thanks for inputs1
 
Originally posted by ThikStik
So Keith, you are basically saying that cap should self align on tork down? If not, then what is built up/welded-cap or block? I do notice that cap's edges are rounded where they meet at block edges. .........

The steel caps must be fit to each block. We start this by setting the block up in a mill and machine the block for the caps. This process is a 4-5 hour job including the align bore. We have done many of these and never had a problem with the caps. They MUST fit very tight when done and repeat position w/o movement after torquing a few times. Studs are always used with steel caps.
 
Thanks Mick. It does fit tightly upon last millimeter or so of meeting block, its just that it doesnt seat consistantly position wise. Glad to know the parts are made OK though. (its not a fault with the caps so it would seem from info heretofore). I suppose its ok to align bore for 3 times? These guys did it twice already-without tork plates first. What's a project unless it takes 3 times the amount of knuckle blood anyway!
Nice to know a T/A block will be there when needed.
Thanks
 
Originally posted by ThikStik
Thanks Mick. It does fit tightly upon last millimeter or so of meeting block, its just that it doesnt seat consistantly position wise. Glad to know the parts are made OK though. (its not a fault with the caps so it would seem from info heretofore). I suppose its ok to align bore for 3 times? These guys did it twice already-without tork plates first. What's a project unless it takes 3 times the amount of knuckle blood anyway!
Nice to know a T/A block will be there when needed.
Thanks

The cap really doesn't have anything to seat it forward and aft, regardless of the machining used. That's why it has to be aligned by tapping the crank front and back. If you use good studs, they will be large enough in diameter to locate the cap more closely. Dowels would be nice but I'd be scared to try to dowel a stock block..not enough meat.
 
I still see the 009 having no dowels as being a potential problem . Just too much chance that a cap will be put on slightly askew of center/or differnt than machinist did it. Actually the thrust cap may be the best/safest of all as there is the self centering action that takes place when rapping the crank.
 
Main Bearings

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We do lots of steel caps including Chevies and the procedures are basically the same. If the cap is not properly fitted in the block, it will walk and destroy bearings, crank and possibly the block too.

In process now is a 3.8 with caps that was done by another shop and only run at the Buick event in Las Vegas for a few runs. Caps walked and already ruined the thrust bearing. There are many shops that can do this properly but it consumes lots of machine time and labor, therefore, it is not cheap to have it done right. It is VERY expensive when NOT done right.

Gene, do not mean to "bash" you, just add some info. Procedures are not the problem between different motors, it is the care and attention to details in general. Yes, Chevy or other brands have different tolerances and specs so this must be considered when machining and assembling an engine.:)


GUESS IM NOT THE ONLY ONE OUT THERE GOING THROUGH THIS WOULDN'T DENTINATION (KNOCK) MAKE CAPS WALK ALOS AND WIPE OUT MAIN BEARINGS. I HAD BEARING #3 IN REAL BAD SHAPE #2 NOT BAD. ONCE I INSTALL NEW ROD AND MAIN BEARINGS I WELL KEEP A CLOSE EYE ON THE FITMENT OF THE CAPS. HERE SOME PICS



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It just seems that there shoud be a more positive way to ensurethat caps are in block exactly the same way each time they are installed. How much care is a machinist (excluding Nick, of course) going to takewhen he installs them, then align bores. Woudnt just alittle difference naturally take place when you get stuff home and assemble it? I remember looking at parting lines and tapping caps to try to meet exactly with block...Im sure my monkee machinist didnt do that! And for that matter, yu cant really rely on doing that anyway, as the parting lines dont line up per se. So i made sure that parting lines of bearings mated up...very hard to see with crank in there. That excludes thrust , of course. Before rebuildin, I had assumed that the bolts would self align the caps , then noticed they do not, before i started this thread. I bet there are alot of guys just getting lucky here.
 
I still see the 009 having no dowels as being a potential problem . Just too much chance that a cap will be put on slightly askew of center/or differnt than machinist did it. Actually the thrust cap may be the best/safest of all as there is the self centering action that takes place when rapping the crank.

If the cap is installed in the block and the machining was good on the block then the cap will fit really tight. Then the block and caps are line bored. Then they are line honed the the final dimension. At this point the cap can only be re- positioned in one plane which would be the front to rear. The amount of slop in the studs to cap will determine the amount of potential variance. It wont matter too much since the bearing surface is adequate and the stack up of tolerances is taken into consideration when the engine was engineered. Doweling is not necessary imo.
 
Program caps

I noticed the same thing with my thrust cap. I reasoned that the thrust bearing can still be set using the correct procedure. The other thing I noticed was that the number 3 Program cap had the main bearing tab machined in the wrong place. It was about a tab width off. The machine shop just ground it wider and made it work. But, I didn't like the tab not fitting tight in the cap. These things are expensive and they should be better than that. I'll have second thoughts about using then again.
 
I noticed the same thing with my thrust cap. I reasoned that the thrust bearing can still be set using the correct procedure. The other thing I noticed was that the number 3 Program cap had the main bearing tab machined in the wrong place. It was about a tab width off. The machine shop just ground it wider and made it work. But, I didn't like the tab not fitting tight in the cap. These things are expensive and they should be better than that. I'll have second thoughts about using then again.

This is a common problem on aftermarket caps and regrinding the tab is no big deal.
 
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