SVX Network Forums Live Chat! SVX or Subaru Links Old Lockers Photo Post How-To Documents Message Archive SVX Shop Search |
IRC users: |
#46
|
|||
|
|||
Re: Engine Bearing Failure
Finally pulled the engine that developed a knock from 3 years ago.
Quick background: Stock bottom end, with original cooling problem (ie, overheated in a blink), then ran a stage of a rally, temps off the scale the whole stage. Bottom end knock. This is the bottom end of cylinder number 5...I think this confirms Tom's comments that number 5 fails. |
#47
|
||||
|
||||
Re: Engine Bearing Failure
Has anybody got any ideas as to why this is happening?
Tony
__________________
1995 - SVX 700,000 K Mine, DMS Struts to lift car 2in. Tyres Wrangler Silent Armor 235/70R16, PBR Radiator. 6 speed with DCCD and R180 rer diff, Heavy duty top strut mounts front and rear. Speedo correction box fitted. New stero (gave up on the old one). Back seat removed and 2 spare tyres fitted for desert driving. ECUTune SC sitting in the box for the next SVX. 1992 - SVX 255 K Wife (Want to stay Married so not allowed to fit SC) 1992 - SVX Pearl with black roof race car roll cauge etc ready to race. Ex Tasman Targa car. 1995 - SVX Green low k mint condiation. 1995 - SVX Rally car, ex Matts car. Now to be used on track. 1992 - SVX red & Black being converted to Mid Engine. 1995 - SVX Red 143,000 bit rough. Owned 5 others Subaru back to a 1974 1400 GSR. |
#48
|
|||
|
|||
Re: Engine Bearing Failure
I can't remember to main bearing oil clearance tolerances but I believe the rod bearings are .0002" on the low side. These clearances could have something to do with it maybe.
EDIT: Oil Clearance Standard Journals No. 1, 3 & 7 ....... .0002-.0014 (.005-.035) Journals No. 2, 4 & 6 ....... .0005-.0015 (.013-.038) Journal No. 5 ............... .0005-.0013 (.013-.034) These oil clearances seem extremely restrictive (.0005 on the thrust bearing). When they get hot there is more thermal expansion and I believe those clearances just won't cut it.
__________________
Cam '92 Ls-L Dark Teal 11:1 CR ECUTUNE pistons ECUTUNE .256 duration intake/exhaust cams ECUTUNE STAGE 2AV1 ECU Z32 MAF/SR20DET injectors Balanced & Blueprinted Last edited by Cam; 08-06-2010 at 06:24 PM. |
#49
|
||||
|
||||
Re: Engine Bearing Failure
Failures are sudden and usually not accompanied by low oil pressure prior to failure. This indicates there is something that happens that allows the bearing to spin right out...
The bearing is getting too hot from an oil film that was too thin. Too hot from an oil that was too heavy with clearances too small. Or my best guess, the rod bolts are stretching at High RPMS which is enough to misshape the bearing. Tom |
#50
|
||||
|
||||
Re: Engine Bearing Failure
Quote:
And why the problem is happening always with #5?
__________________
Danny 1994 Silver SVX in hybernation, awaiting for the monsterous awakening (Lebanon) 1967 Mercedes-Benz 250SL Euro Specs, Hard/Softtop, White/Red. Under Complete Restoration 2013 Mercedes-Benz SL350 Euro Specs, White/Red. Mint... Another step into SL Collection. |
#51
|
||||
|
||||
Re: Engine Bearing Failure
Quote:
Not always #5... but it is late in line for oil and it is on the thrust bearing feed... Not entirely sure Tom |
#52
|
|||
|
|||
Re: Engine Bearing Failure
Thrust bearing feed? Without the book in front of me, what could that mean?
And other than #5, what others have you seen go Tom? M |
#53
|
||||
|
||||
Re: Engine Bearing Failure
#2, #4, & #1
No real logic to it but the stretching theory holds a little Merritt. Reason being, the rest of the bearings don't look overheated or worn out totally like you would see if there was an oil system error or fault. Its simply is the first bolts to stretch and cause an issue while slinging the bob weight around at high RPMS Tom |
#54
|
|||
|
|||
Re: Engine Bearing Failure
Is there a way to identify if stretch was the culprit? Are there obvious signs? Or is it just measuring bolts?
|
#55
|
|||
|
|||
Re: Engine Bearing Failure
Quote:
__________________
Cam '92 Ls-L Dark Teal 11:1 CR ECUTUNE pistons ECUTUNE .256 duration intake/exhaust cams ECUTUNE STAGE 2AV1 ECU Z32 MAF/SR20DET injectors Balanced & Blueprinted |
#56
|
||||
|
||||
Re: Engine Bearing Failure
Quote:
The factory bearings are AL. meant to withstand high mileage not high heat Tom |
#57
|
||||
|
||||
Re: Engine Bearing Failure
Other than a super expensive drysump system, any ideas how we can permanently fix this problem?
__________________
Danny 1994 Silver SVX in hybernation, awaiting for the monsterous awakening (Lebanon) 1967 Mercedes-Benz 250SL Euro Specs, Hard/Softtop, White/Red. Under Complete Restoration 2013 Mercedes-Benz SL350 Euro Specs, White/Red. Mint... Another step into SL Collection. |
#58
|
||||
|
||||
Re: Engine Bearing Failure
Stock components are not gonna hold up to 7500RPM abuse for long. You have the lighten the rotating assembly using high quality parts and make sure the oiling system is perfect with the proper clearances
Tom |
#59
|
||||
|
||||
Re: Engine Bearing Failure
Quote:
As a means of guarding against stretch and fatigue, it is accepted practice in these circumstances to tighten the big end bolts in excess of normally specified torque figures. The proper way to do this, is to first tighten a sample and measure the stretch while noting the torque applied, until the elastic limit is found and then be guided accordingly.
__________________
Trevor, New Zealand. As a child, on cold mornings I gladly stood in cowpats to warm my bare feet, but I detest bull$hit! |
#60
|
||||
|
||||
Re: Engine Bearing Failure
Quote:
I agree it could be overheating as well but since the stock engines I have taken apart without failures (not raced either) show relatively equal measurements for film clearance I would not put money on just one bearing overheating while the others show no signs of it. I am not saying its not possible, just saying I believe the answer is not so cut and dry Tom |
|
|