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Thread: Blown Engine

  1. #1

    Default Blown Engine

    Ok, need some opinions here. Have a (had) fresh built 2.5 short block from (not going to say yet).Only made it 4 & 1/2 practice laps, then BOOM!! Oil pressure - 50-55, water temp only made it up to 170. #1 & 2 rods broken, & crank turned blue on those two as well as bottom of rods. When taking the rods off1 & 2 were not tight. # 2 rod left bolt was not much more that finger tight. # 3 & 4 seemed to be as they should be.There was no bearing left on 1 & 2, only fragments everywhere. 3 & 4 bearings were there but were shot.I was told the timing was too much (36) that I've run on the 2.0 & 2.3, & that the rod bolts streatched making them loose.In 30 years of being around race cars & blown engines, I've never noticed this before. I had the Canton pan & pick up& was told to use the turbo oil pump.Thanks for any thoughts you may have, & I'll try to answer any questions as best as I can. F-9

  2. #2
    Join Date
    May 2007
    Location
    Thurston, OH
    Posts
    915

    Default

    I suspect that whoever 'built' your 2.5 'failed the test' on rod bolt installation. Every 2.0/2.3/2.5 I've ever built? I use ONLY ARP rod bolts with their lube. And before final assembly, I go through a procedure with rods & their ARP bolts. I clamp the rod between two bars of aluminum on my bench vise. I assign specific bolts to every rod and hole they'll be used in. And write it all down on paper. I first measure the 'free length' of the rod bolt with my JEG'S bolt-stretch tool. Then install the lubricated bolts in the bench-vice clamped rods and gently tighten them. Then I use the torque-wrench and tighten the bolts to the ARP recommended torque. I bounce back and forth between bolts and tighten them in 10# increments. Then I use the JEGS tool to measure how much the bolts had stretched. If they hadn't stretched enough, I loosen the bolts, go through the tighten process again, and add 5# of torque. Then re-check the stretch. I write it all down on paper, then when I assemble the engine I simply use the final torque values I documented. Works for me every time! I've never lost an engine due to a rod bolt problem. -Dave-

  3. #3
    Join Date
    Apr 2015
    Posts
    27

    Default

    what kind of rpm,not that that would matter just wondering,measure your rod bolts now and see what stretched

  4. #4

    Default

    Thanks for the input as always guys. I was turning 76-78. I was told it would stand in the 8+ range. There was a .017 range from the longest bolt to the shortest. I figure the extra stretch was from not being tight, plus the heat from that & extra movement in the crank.

  5. #5
    Join Date
    Apr 2015
    Posts
    27

    Default

    i would now check the part# and size of the bearings and your rod side clearance and the radius of the crank journal filit,and look for any obvius signs of interference

  6. #6
    Join Date
    May 2007
    Posts
    2,186

    Default

    Number 1 rod bearing is the last to oil and first to tear up when an oiling problem exists.
    BUCKLE UP NOW, YA HEAR?

  7. #7

    Default

    It had 50-55 lbs max. I was told by Race Engineering (who built the engine) that was plenty. I've been told by other engine builders it should be 10 lbs per 1000 RPM"s. The hightest I got was 7800. I didn't really want to run it wide open until I had some laps on it. I'm still waiting on their response. I guess I'll find out what kind what kind of company they are. They've always treated me well in the past, but nothing on this level.

  8. #8
    Join Date
    Sep 2007
    Posts
    181

    Default

    I would pull main caps and see where oiling problem started

  9. #9

    Default

    All the mains looked ok, except where trash got through the oil pump. I've looked at this thing over & over, & I keep coming back to the rod bolts being loose on 1&2. they were noticibly not tight. 3&4 were tight as should have been.

  10. #10
    Join Date
    Sep 2007
    Posts
    181

    Default

    next ,crankshaft was not cleaned inside . burn bearing bolts will stretch

  11. #11

    Default

    Not sure how to check that now that it's probably full of bearing fragments now. #3&4 bearings were still in place but were down to the copper. main bearings were good

  12. #12

    Default

    Well, I was just told that the cause of my engine failure was too mush timing, 36. I just dont see all that damage in just 4 laps total on that engine. Just practice, not full race laps.

  13. #13
    Join Date
    Apr 2015
    Posts
    27

    Default

    whats the comp ratio, and what fuel

  14. #14
    Join Date
    Sep 2007
    Posts
    181

    Default

    too much timing will not get bearings ,it will burn pistons most of the time. did you set timing above 3500 rpm's.or locked dist.1000 rpm's if so, not 36 degree timing at fault

  15. #15

    Default

    I'm not sure about the compression at this time. The head is cut just before the intake bolts showing. Running Cam2 blue fuel. I was thinking the same as you Dave. We had the timing at 36 @ 3000 RPM's. Race Engineering said 36 is too much for the 2.5 & causes too much cylinder pressure sqeezing oil out from between the crang & bearing. They also said it's not due to lack of oil, but by overpowering the hydraulic pressure at the rod bearing.

  16. #16
    Join Date
    Sep 2007
    Posts
    181

    Default

    we have run 15-1 compression and never squeezed the oil from between the bearings and rods. bull crap.

  17. #17
    Join Date
    Sep 2007
    Posts
    181

    Default

    you can't turn 7600 rpm's with 20 degrees timing advance 35-36degrees for 7600 rpm's is about right. you have to advance to keep up with rpm or your timing will start to get behind your rpm's. 8200 you may have to go to 37 degrees

  18. #18

    Default

    Thanks Dave!! They keep telling me the 2.5 is different because of the stroke. I'm real sure I don't have as much compression as you do. They keep telling me the bolts being loose was because of the heat caused by that cylinder pressure that streached them. I don't buy it. I think the bolts were loose causing the rods to beat the bearings out, causing the heat, that destroyed the engine. I'm no engineer by any means, but I don't buy their story. I just dont have any way to prove it.

  19. #19
    Join Date
    Apr 2015
    Posts
    27

    Default

    i second the previus last 2 replies, from dave 41
    Last edited by themotorshop; 08-18-2016 at 02:38 PM.

  20. #20
    Join Date
    May 2007
    Posts
    2,186

    Default

    I've built enough 2.5 engines that ran MORE than 36 degrees timing with compression levels beyond where you are.

    Excessive timing can take out bearings and low octane fuel for the CR can take out engines in about 4 laps. I'm not looking at the parts but I can tell you that 36 degrees isn't hurting a 2.5 engine. Period.

    What took out your engine I do not know without pictures or something to go by. But you can bet your ass that it isn't from 36 degrees of timing.
    BUCKLE UP NOW, YA HEAR?

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