rebuilt 6bolt crankwalking twice

[311GSX]

Ok heres the problem,the first rebuilt motor crankwalked after 500 miles. the second rebuild is stalling when the clutch is pressed, the crank is grinding the thrust bearing. I have a new oil pump and the pressure is good for some reason there isn't enough oil pressure at the thrust bearing and I don't know why.I know its not a clutch problem b/c it was fine before and everything is new, even a differnt clutch than the first crankwalked motor.oil squirters maybe?but im not sure that would releve enough pressure in the main gally to starve the bearing.I've searched and read just about every crankwalk post so don't post a link i've already read it.please some one help.

Bob

 

[defrag010]

Builder error, or the thrust surface on the block/maincap is not straight.

 

[playitlouddsm]

When you put it together did you check to make sure you had enough oil clerance between the bearings and crank?

 

[311GSX]

I took it apart yesterday and found the thrust bearing was misaligned, I checked the clearence when I assembled it but for some reason it wasn't straight when I took it apart

 

[defrag010]

Yea, that's important to make sure the clearances are the same before and after being torqued down. I spent about an hour trying to get my thrust aligned on the last motor I built, and I ended up having a friend pry on the crank towards the oil pump while I torqued down the maincaps.

 

[1fast97gsx]

yea ... I knew there was a reason I spent 35 minutes just aligning that thing and checking / rechecking it again and again when I did mine.

 

[Big Woo]

First off don't bother checking the oil clearances before torquing, as they will be meaningless. As bearing crush comes into play, and this does not occur until torquing.

Crankshaft endplay can be measured before installing the center #3 main cap. However DO NOT USE THIS MEASUREMENT AS A FINAL DIMENSION. The main reason for doing this would be to verify, that there is no interference fit problem with the crankshaft thrust surfaces, and/or to verify where the problem may be. Additionally this information could be used to verify that the #3 main cap is installed correctly. For example if you are using a magnetic stand and a dial indicator, position it so that indicator makes contact with a surface of the crankshaft that is perpendicular to the long axis of the crank. Lightly hold the in either its full forward or rearward position and zero the indicator, then move the crank in the opposite direction and again lightly hold it in position, and read the indicator. If you get .008 of endplay, without the center main cap, you should get .008 after the center main cap is installed and torqued. If not then there is a missalignment somewhere.

I use a Delrin wedge to position and hold the crankshaft, but a large screwdriver can be used by the do it your selfer, just be careful and do not use excessive force. And if using a screwdriver or other hard tool make certain it does not come into contact with any of the bearing surfaces. The wedge or screwdriver can be placed between one of the crankshaft counter weights, and one of the main webs, to position and hold the crank in either its full forward or rearward position. AGAIN DO NOT USE ALLOT OF FORCE HERE, WE ARE JUST TRYING TO MEASURE THE AVAILABLE ENDPLAY: NOT TO SEE HOW MUCH WE CAN CREATE
When installing the center main cap have the wedge in place prior to installing the cap. This way when the cap is installed and torqued it should be butted up against the crankshaft thrust surface, helping to maintain alignment. Also when torquing, pull the torque wrench toward the butted surfaces. After torquing is complete (REMOVE THE WEDGE) and remeasure crankshaft endplay, and verify it to the specification.

Also of note here; many crankshaft endplay problems occur because of a perpendicularity problem between the thrust bearing caps block mating surface, and the cap machining for the thrust bearing itself. This can also occur from "cap walking" where under stress the cap and block mating surfaces rub against each other, causing both to wear. Additionally if the block, has been alignbored or alignhoned this problem can be created. Since during this process the main caps must be cut to reduce the main housing diameter, so that it may be bored or honed back to their original size. Sometimes in the cutting or grinding process on the main caps, the caps surface may not be cut absolutely perpendicular to the thrust surface, and this can cause the lower thrust bearing half to sit at a slight angle as compared to the upper half. Therefore by checking endplay before and after the installation of the thrust bearing cap, one can ensure that the cap and thrust surfaces are properly aligned.

 

[311GSX]

I got the motor back together and its doing the same thing and the thrust is lined up, I think its an oil pressure problem tho. at idle the gauge reads 2.0kg/cm2 which if my conversion is right is ony 4.4 psi of oil pressure at idle. anyone know why that would be?

 

[Big Woo]

Quote:
I got the motor back together and its doing the same thing and the thrust is lined up, I think its an oil pressure problem tho. at idle the Gage reads 2.0kg/cm2 which if my conversion is right is only 4.4 psi of oil pressure at idle. anyone know why that would be?




When you put the motor together how much crank endplay did you have? What were the oil clearances for the rod bearings, main bearing, cams, oil pump etc?

Off the top of my head here are some of the things that determine oil pressure. You will want to verify that all of the clearances are within specification. Also verify that there are no external leaks.

Rod and main bearing oil clearance, connecting rod side play, oil pressure relief valve and spring, oil squirter's and check valves, oil distribution block for cylinder head, oil pump drive & driven gear Clarence, balance shaft bearings Clarence. lifter fit to cylinder head, cam journal oil Clarence, oil feed lines within block and head, front case/oil pump gasket, etc.

Essentially oil pressure is determined by the output pressure & volume of the oil pump, minus the flow rate of the leaks in the system, or pressure drop if you will. Basically every oil Clarence is a leak, the oil is forced into a space through some sort of a feed line, moves through that space, and returns back to the sump. When it is feed into a space it has a positive pressure, and as it leaves that space its pressure falls to zero.

If your oil pressure is to low, then you have to big of a leak or leaks within your system.

 

[tmizer]

What BW said, except "clarance" is spelled "clearance".

Some specific things come to my mind:

Did you do a balance shaft eliminator kit? If so, when you tear it apart again, check the rotation of the 2 bearings.

While rare, you might check the oil pump pickup tube/strainer. Make sure it's not cracked, split, etc.

 

[hostile]

I got the motor back together and its doing the same thing and the thrust is lined up, I think its an oil pressure problem tho. at idle the gauge reads 2.0kg/cm2 which if my conversion is right is ony 4.4 psi of oil pressure at idle. anyone know why that would be?

Just fyi 2.0 kg/cm2 is around 28psi.

1 kg/cm2 = 14.22

 

[311GSX]

thanks for the info I guess the oil pressure is good