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Discussion Starter #1
Curious what you guys think. About a month or so ago my oil pressure dropped about 10lbs. Pulled the main and rod bearings and had one spun main bearing. So we just rolled in a new set that was the same brand and size. The crank looked fine in that spot. Never pulled heads or front cover, etc.. Drove the car the last month with good oil pressure and after 5 passes it's doing it again. I am suspecting a bearing failure again. I realize I am pushing this engine to the limit and it may be as simple as that.

This time I will pull the crank and have it checked. If the crank is not bent I am wondering what issue might be causing this. The only thing I can think of is I run the stock flywheel and I dremel out the holes for my convertor to fit. I would think as long as it the snout is fitting in it shouldn't be an issue. However, since I have done this again after only a months driving and 5 passes I am wondering if I should get an aftermarket flywheel.

Its a stock 6.0 out of a 2005 denali. I run twin SW366's on E85. My last pass was friday and it went [email protected] leaving on 4lbs of boost. Yesterday I tried to leave on 9lbs and that was when I noticed my oil pressure was lower. Today I started it up and it was still about 10lbs lower even cold. Car sounds and runs fine. fwiw
 

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Discussion Starter #3
is it the middle main?
It was last time. I am suspecting the same. I drained the oil and there is definitely gold metal flakes in it. Not much but definitely is. My oil pressure is around 40 at idle and goes up to about 55. However, it was 50 and would go up to 70.

What's up with the middle main?
 

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Discussion Starter #7
Rebuild the mother fucker... before you blow the whole thing upFordSux:
It isn't going to do any good to rebuild it if I don't know what keeps causing it. I would like to know what is causing the failure before I rebuild it or replace it.

Its a PTC convertor, how would the convertor cause it?
 

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Discussion Starter #8
this

show us what the thrust looks like when u get it apart
Okay. Can you explain how the convertor would do it. That would make sense though only because both times this has happened is right after having the trans rebuilt. Just put my TH400 back in this time. Same convertor.
 

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Okay. Can you explain how the convertor would do it. That would make sense though only because both times this has happened is right after having the trans rebuilt. Just put my TH400 back in this time. Same convertor.
internal fluid pressure of the converter turns the converter into a hydraulic jack over the area of the opening in the converter


i would put it on a transmission issue and not the converter if it is the thrust taking beating, if you where running a glide, the input shaft selection and converter charge and exhaust circuits need to be matched properly

same goes for the 400

if you can check the cooler pressure on the trans on the transbrake it will give you an idea of what is happening in the converter
 

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Which bearing shell looks the worst?? If it is the top one you are exceeding the load capacity of the crank. This usually occurs in large cuin small blocks with a lot of load and rpm. The answer to a big SB is usually go to a center counterweight crank similar to a BBC crank. This was common practice on high hp builds even if it was a Bryant or Callies billet while I was at KUP. I have also seen it on big SBC's as well. After considering this post, go back and look at both sets of failed bearings and try to find the root cause. Posting pics or link to pics would be great and hopefully we can resolve this before anymore damage can be done. Hope this helps.
 

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Discussion Starter #11
internal fluid pressure of the converter turns the converter into a hydraulic jack over the area of the opening in the converter


i would put it on a transmission issue and not the converter if it is the thrust taking beating, if you where running a glide, the input shaft selection and converter charge and exhaust circuits need to be matched properly

same goes for the 400

if you can check the cooler pressure on the trans on the transbrake it will give you an idea of what is happening in the converter
Well this is over my head. I just threw my Th400 in. I was told the input shaft would work. That is all I know.

Which bearing shell looks the worst?? If it is the top one you are exceeding the load capacity of the crank. This usually occurs in large cuin small blocks with a lot of load and rpm. The answer to a big SB is usually go to a center counterweight crank similar to a BBC crank. This was common practice on high hp builds even if it was a Bryant or Callies billet while I was at KUP. I have also seen it on big SBC's as well. After considering this post, go back and look at both sets of failed bearings and try to find the root cause. Posting pics or link to pics would be great and hopefully we can resolve this before anymore damage can be done. Hope this helps.
The last time I think it was the bottom bearing. This time I will take pics and make a note when I pull it and take it apart. It might be a while. I will post the pics once I do.

Thanks.
 

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After eating a couple thrust bearings (and cranks) I just put a 150 psig sensor on my trans cooler loop. No data until it stops raining long enough to run it once. Mine also started with a transmission rebuild where a number of relevant parts were changed.
 

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Before you take it apart, check the crank thrust. Don't know what it is for that engine but I imagine it's similar to a SBF - .006" to .008".

Also, unbolt the converter push it back and check clearance. Should have 5/16"-3/8" I believe for most combinations. Make sure the converter "snout" is free, centers in the crank and can move freely in/out.
 

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Sounds like the converter has been deemed the culprit without anything to verify.

Maybe too much ignition timing killed the first set of bearings. The crank is no longer round or heat checked or both. If bearings don't last rolling in another set, either the tune up issue has not been corrected or the crank needs machined.
 

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Does the flywheel use a pilot bushing adapter? How are you spacing the converter into the pump?

Could be transmission not converter. Lots of guys have to tweak the pressures on th400's. ATFspeed actually has a nice external regulating kit.
 

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Before you take it apart, check the crank thrust. Don't know what it is for that engine but I imagine it's similar to a SBF - .006" to .008".

Also, unbolt the converter push it back and check clearance. Should have 5/16"-3/8" I believe for most combinations. Make sure the converter "snout" is free, centers in the crank and can move freely in/out.
This is too much and runs the risk of not enough engagement on pump. Every converter company I have dealt with say .125 to.187 with .150 being the ideal amount. I have always had something in this range and never had any thrust issues. I have seen a lot of issues from tuneup being slow to spool and/or being on the 2-step too long. I know there are some legitimate trans and cooler circuit pressure issues but not what I would check first. Verify the converter spacing and if it takes longer than 3-4sec I would work on the tuneup to get this as low as possible. As far as thrust clearance it's usually .005-.010 and I might lean toward one end or the other based on oil, type of power adder, any other thrust mods.
 

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Discussion Starter #17
I do not use an adapter. I did check the clearance before the convertor and flywheel and put in a washer to give me 5/16. I will check the thrust. When we put this Th400 in it would not easily go into reverse. I had to give it some gas each time. I was told that is normal on TH400's. Is this the pressure we are referring to?

As far as too much timing doing it. The car ran fine for almost a year and I run way less timing now then I did then.
 

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I do not use an adapter. I did check the clearance before the convertor and flywheel and put in a washer to give me 5/16. I will check the thrust. When we put this Th400 in it would not easily go into reverse. I had to give it some gas each time. I was told that is normal on TH400's. Is this the pressure we are referring to?

As far as too much timing doing it. The car ran fine for almost a year and I run way less timing now then I did then.
5/16 is 1/4 too much by most converter company specs, but I would check the specs on your converter. As said above, 1/8 to 3/16 is norm.
 

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5/16 is 1/4 too much by most converter company specs, but I would check the specs on your converter. As said above, 1/8 to 3/16 is norm.

Yep, my bad. It's been awhile since I had to set one up and was going by my foggy memory. 1/8"-3/16" is what I remember now was right.
 

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how much main bearing clearance do you have what weight oil how much max boost how much oil pressure @ wot
 
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