Engine autopsy help
Discussion
After a self inflicted bottom end failure at oulton park last October I had to rebuild my Saab b234 and used a good used crank that was checked and polished by my regular machine shop before building , engine cleaned thoroughly and used a brand new set of pec rods and new wrist pins . I've built a few engines with this recipe but opted for the new arp super duper rod bolts which is the only difference . Cold oil pressure was 75 psi dropping to 35 at warm idle . These motors do clatter a bit while the lifters fill up and once it warmed up I thought I could hear something odd but very light but a quick drive up the road was not good .
Pulled the sump off and found this lot
1and 4 mullered and no 3 loose in the rod .
The rod bolt torque setting is twice the value of the std arp bolts ,
I'm thinking the rod bolts have pulled them out of shape as I've done a few with the std arp bolts and no problems . Last time I came across a out of round rod it grabbed the crank but this went together fine and used a fishing scale to measure drag as it went together .
Pulled the sump off and found this lot
1and 4 mullered and no 3 loose in the rod .
The rod bolt torque setting is twice the value of the std arp bolts ,
I'm thinking the rod bolts have pulled them out of shape as I've done a few with the std arp bolts and no problems . Last time I came across a out of round rod it grabbed the crank but this went together fine and used a fishing scale to measure drag as it went together .
rod bolts already look a decent size ?
If you're needing more than an ARP2000 there, you must be pulling some insane rpm's !
Mains certainly look ok. But when you say hot oil pressure is 35psi, is that all the time ? No higher when rpm rises ?
Can you torque a rod up and check the hole for roundness ? Both with normal torque and whatever the high torque was you used ?
If you're needing more than an ARP2000 there, you must be pulling some insane rpm's !
Mains certainly look ok. But when you say hot oil pressure is 35psi, is that all the time ? No higher when rpm rises ?
Can you torque a rod up and check the hole for roundness ? Both with normal torque and whatever the high torque was you used ?
35 psi hot idle but it idles at 1050rpm rather than 850 as the water pump struggles at idle having the motor at the back . It just doesn't add up that one big end is perfect and the Mains good if it was oil related . I've dug out an old set of rods and the caps off the new f
ked ones are miles off fitting so I'm assuming they're egged . 60psi at 3500 hot .
ked ones are miles off fitting so I'm assuming they're egged . 60psi at 3500 hot . One would have thought, had the rod started to distort from round due to overtightening ( I would have thought a bolt would shear or neck before the rod distorted?) The bearing would have nipped on the crank journal as clearance would be in the 1 ish thou region and would have gone with distorted big end housing in the rod. Were the rod bolts loose when you stripped it?
Another possibility is ovality and or taper of the crank journals or even poor bearings. I mention this as the mains look like they have had loading favouring one side and that favouring tell tales show the bearings are not round in fitment and under running conditions.
If you haven't already done so it would be worth buying bore gauges to check main bearing caps, big end caps and little ends. The same applies to micrometers to measure the crank for taper, ovality and size.
Peter
Another possibility is ovality and or taper of the crank journals or even poor bearings. I mention this as the mains look like they have had loading favouring one side and that favouring tell tales show the bearings are not round in fitment and under running conditions.
If you haven't already done so it would be worth buying bore gauges to check main bearing caps, big end caps and little ends. The same applies to micrometers to measure the crank for taper, ovality and size.
Peter
Edited by PeterBurgess on Friday 8th January 06:45
Edited by PeterBurgess on Friday 8th January 06:51
I seem to remember raising an eyebrow when I read your discussion on FB about this and you said the torque settings were twice as much. You've either been misinformed or got NM and Lbs/ft mixed up perhaps.
That aside a few points spring to mind.
Use of:
An ARP bolt stretch gauge.
Plastigauge - This is so cheap and simple and may have saved you.
Feeler gauges placed in the gap between the face of the rod and the web of the crank whilst torquing up.
I'm not against the use of cheap rods because they do the job, but you do have to be extra vigilant and check everything on them carefully, they do throw a rogue one in now and again which you wouldn't expect with Arrows etc.
Extra strength rod bolts are for excessive RPMs with expensive rods.
A turbo engine is all about mid range torque and power so you shouldn't need to rev the tits of it, if you are having to do that then maybe your spec is wrong, either the gearing or engine spec. You can make 5 - 600 bhp before 6 - 7000rpm on 2ltrs so you should be making 450 on a 2.3 in less than 6000 easily.
Obviously making the power required at less rpm has a marked effect on engine longevity....
That aside a few points spring to mind.
Use of:
An ARP bolt stretch gauge.
Plastigauge - This is so cheap and simple and may have saved you.
Feeler gauges placed in the gap between the face of the rod and the web of the crank whilst torquing up.
I'm not against the use of cheap rods because they do the job, but you do have to be extra vigilant and check everything on them carefully, they do throw a rogue one in now and again which you wouldn't expect with Arrows etc.
Extra strength rod bolts are for excessive RPMs with expensive rods.
A turbo engine is all about mid range torque and power so you shouldn't need to rev the tits of it, if you are having to do that then maybe your spec is wrong, either the gearing or engine spec. You can make 5 - 600 bhp before 6 - 7000rpm on 2ltrs so you should be making 450 on a 2.3 in less than 6000 easily.
Obviously making the power required at less rpm has a marked effect on engine longevity....
They are the 3/8 so 60 ft lb and if need to double check but the 2000,s were 43 lb/ft and I've done three engines with the 2000,s .
I don't have stretch gauge etc and the only rod that's survived must be ok size wise looking at the bearing . The Saab tuning scene isn't huge and I don't know anyone else who has used these bolts yet . I don't need to run past 6500 rpm and it did 90% of its time on track days
PeterBurgess said:
One would have thought, had the rod started to distort from round due to overtightening ( I would have thought a bolt would shear or neck before the rod distorted?) The bearing would have nipped on the crank journal as clearance would be in the 1 ish thou region and would have gone with distorted big end housing in the rod. Were the rod bolts loose when you stripped it?
Another possibility is ovality and or taper of the crank journals or even poor bearings. I mention this as the mains look like they have had loading favouring one side and that favouring tell tales show the bearings are not round in fitment and under running conditions.
If you haven't already done so it would be worth buying bore gauges to check main bearing caps, big end caps and little ends. The same applies to micrometers to measure the crank for taper, ovality and size.
Peter
I'm not an engine builder by any stretch but have done three engines with the 2000 bolts that come as std with the pec rods and no issues , I follow the guide and run the bolts up twice before final torque and use a pull scale to check drag as the rods went in and it felt right as I would have expected the bearing to grab the crank as it measured up fine . They are cheap rods but have worked fine and I've had my own motor apart to check and the old bearings showed no signs of uneven wear with the 2000 bolts Another possibility is ovality and or taper of the crank journals or even poor bearings. I mention this as the mains look like they have had loading favouring one side and that favouring tell tales show the bearings are not round in fitment and under running conditions.
If you haven't already done so it would be worth buying bore gauges to check main bearing caps, big end caps and little ends. The same applies to micrometers to measure the crank for taper, ovality and size.
Peter
Edited by PeterBurgess on Friday 8th January 06:45
Edited by PeterBurgess on Friday 8th January 06:51
Were any of the rod bolts loose to the feel when you undid them? I would have thought, had the bolts stretched or had the caps collapsed you would have had an effect such as the bolts losing tension. I know you have cheap rods but I would be surprised if you managed to squash them with the rod bolts. Why not see if you can squash the one that hasn't failed? The difficulty is working out where the failure started. With future builds unless you measure all the cranks and bores and rods and main bearing caps yourself you will never know if they were right to start with. As Evoluzione says, why not use plastigauge so you can measure the bearing clearance?
We send our blocks and cranks to Cylinder Rebores, Tenlons Road Industrial Estate, Tenlons Rd, Nuneaton which is a long way from us, but, we feel, well worth it for the quality and consistency of work they do for us.
Peter
We send our blocks and cranks to Cylinder Rebores, Tenlons Road Industrial Estate, Tenlons Rd, Nuneaton which is a long way from us, but, we feel, well worth it for the quality and consistency of work they do for us.
Peter
Something seems wrong here, the torque setting for 2k bolts 3/8 x 1.5 is between 45 and 55 ft/lbs (dependent on rod manufacturer), that isn't 50% less ?
I would say 61 for those is correct though.
Mind you, if you aren't going to answer any questions directly i'm not sure how anyone can be of help....
I would say 61 for those is correct though.
Mind you, if you aren't going to answer any questions directly i'm not sure how anyone can be of help....
I built them the same way I've done before and being brand new rods I didn't check them for twist just deburred them and cleaned them .
Didn't use feeler gauges whilst torquing them up but as I said I'm not an engine builder . Now the rods are properly fked measuring is a bit pointless but from my point of view the crank was checked for size , brand new rods and obviously bearings built up in the same way I've done a few times the only difference being the rod bolt
Didn't use feeler gauges whilst torquing them up but as I said I'm not an engine builder . Now the rods are properly f
ked measuring is a bit pointless but from my point of view the crank was checked for size , brand new rods and obviously bearings built up in the same way I've done a few times the only difference being the rod bolt mighty kitten said:
They are the 3/8 so 60 ft lb and if need to double check but the 2000,s were 43 lb/ft and I've done three engines with the 2000,s .
I don't have stretch gauge etc and the only rod that's survived must be ok size wise looking at the bearing . The Saab tuning scene isn't huge and I don't know anyone else who has used these bolts yet . I don't need to run past 6500 rpm and it did 90% of its time on track days
And you're comparing torque specs for two different sizes of fastener there....and given the strength of the bolts vs some rods, I'd fully expect the rod to go pear shaped before a bolt breaks, especially when you've just bought some of the strongest bolts out there paired with budget rods.
Some people even say not to ft ARP bolts to factory rods because the rod can deform when torqued.
Torque the rods up and measure the hole at either torque level, although they're maybe just totally screwed.
Although if they were pear shaped because of torquing, I'd have thought you would feel this when building the engine and trying to turn it over by hand.
As Stevie says he would expect deformation to nip the bearing on the crank. As this did not happen you could assume the rod did not deform or, if it did deform, the clearance was already large enough to accommodate the deformation, implying the clearance was too great to start with, hence Evoluzione suggesting you measure clearances in the first place.
Peter
Peter
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