Sale ends todayGet 30% off any course (excluding packages)

Ends in --- --- ---


Build Threads

Forum Posts



Tech Articles

Keep everyone up to date with how your project is coming along. 

= Resolved threads



I am facing a problem with the main bearings ( evo 8 7 bolts ) rpm 9500 . this is the 4th engine same problem on high boost 42 psi it kills the main bearing and one time the rod walked out the block . power is 900 whp on a load dyno ( ethanol afr 11.3 ) big ends bearing is 0.0020 inch main is 0.0025 inch . Aluminum rods 156 mm , liqui moly oil. modified gear oil pump , crank balance deleted . some ppl adviced me to use 6 bolt crank and block but i still want to try one last time . sold engine and transmission mounts ( you this this is the problem bcuz vibration ) , dog box , fully build head 296 -300 camshaft hydro .\any idea ?? any suggestion ? where to dig to find the problem ? help me the clearances if im wrong .

thank you so much and sorry for the mess i wrote but i need to fix it .

What engine oil thickness do you use?

Also, with that much power i would go with a little bit bigger bearing clearance - 0.0029-0.0032...

Can you post some images of the failed bearings, and can you tell us the brand and type?

That said, I would suspect the problem lies elsewhere - there are known issues with the oil pump cavitating at such high rpm - have you been logging the oil pressure, preferably as far from the pump as possible?

If possible, I would suggest converting to a dry sump, if it saves just one rebuild, it will be money very well spent.


Liqui moly 10 40 also tried 5 50 . Oil pressure reachs 145 psi at high rpm .

Plz check picture attached

Attached Files

Well, the picture clearly shows the contact taking place all over the entire surface which would be indication of oil starvation...I think Gord is absolutely right and your engine is lacking oil pressure at such high rpm level.

PS I use 10w60 racing oil with 0.003 bearing clearance


Does this oil pressure accumulater helps ?

Check attached pic plz

Attached Files

As Gord previously wrote the problem is with stock oil pump - it is cavitating at very high rpm which means it is not performance issue in the first place but design. This pump is just not designed to work at such high rpm range. That is why going to dry sump system would be sound way to go...

What if I go low with RPM , 8600 instead of 9600 ?

no dry sump now .

Thank you

what is the application for the car ?

alloy rods suggest drag racing

do you have logs we can look at

as mentioned above the oil pumps are a issue at hi rpm,

But with out seeing more evidence (data) i would not like to assume it is the issue

logs are the key thing to share with us to help

Regards Ross

Lowering the rpm that amount 'should' take cavitation out of the equation, but if the engine is otherwise built to produce power at higher rpm, it is being wasted - a dry sump can also increase power as there may be less parasitic draw on the engine from the pump and reduced windage. I understand these engines can also have a problem with excess blowby holding oil in the head*, and so potentially lowering the oil level in the sump, which would further increase cavitation potential.

An Accusump may, indeed, help or even 'cure' the oil supply problem but is more a band-aid than actual cure.

As Ross mentions, and I forgot to earlier, there seems to be several problems evident in the picture -

Alloy rods aren't able to provide the same amount of 'crush' as a steel rod and, to prevent bearings spinning, they commonly use a locator in the cap that locks the shell in place via a hole in it - this is apparently missing and from the condition of the surrounding area, it looks like it was removed deliberately at some point - this increases the chance of spinning a bearing hugely - at best, in a steel rod, the tangs are said to provide ~10% of the resistance to spinning and the rest is provided by the crush. Has that locating dowel been removed?

There has been some thread pick-up, or stripping, as evident on the bolt - there should be NONE(!), that there is suggests the bolt was overtightened and started stripping the thread which would have weakened the clamping force; the bolt was thread damaged and tore the thread in the rod as it was removed; that some form of thread locking compound was used rather than the correct lubricant and this would have compromised the actual tension on the bolt, possibly allowing the cap and rod to separate slightly and remove what crush there was.

It is hard to be sure, but there seems to be a slight green tinge is some areas where the shell sits in the cap - please tell me the shells and connecting rods were CLEAN and oil free, and no locktite, or whatever, was used?

*Running a partial vacuum in the crankcase, with the dry sump scavenge pumps, will reduce the crankcase pressure and aid oil return - and if required, one wafer can be added for head scavenging.

Going through some other stuff and came across a couple of links that may be of interest - the latter because many of the conversions require the customer to do a lot of parts' chasing for things not included, but this one seems a complete package - if nothing else, read their accompanying article!



This is a rather nice looking integrated pump-sump package, but is quite expensive and looks to need a lot more part sourcing for things like tanks, hoses, etc.


This is more complete, and moderately expensive, but will still need some additional hoses, etc.



Attached Files

It's hard to say, but that looks like it may be partly due to debris in the oil supply - main bearings are usually less susceptible to oil pressure fluctuations and there doesn't seem to be the heat discolouration that one might expect.

I cannot stress how important it is to check, double and triple check and clean an engine and it's oilways after a failure! Where possible, remove plugs and run brushed through them before high pressure flushing. A common error is also re-using oil coolers that are contaminated - some companies will take them apart and thoroughly clean them, but better to consider them a disposable item if there's ANY doubt. Don't forget the hoses and other fittings, like thermostats, if used.

It really would help if you showed ALL the shells, main and big end.

I really appreciate your help and suggestions

I'm moving to a new engine 6 bolts engine .

And will post everything here before I start .

Rpm 8700 , delete crank balance .

Thank you

We usually reply within 12hrs (often sooner)

Need Help?

Need help choosing a course?

Experiencing website difficulties?

Or need to contact us for any other reason?