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V8 Crankshafts

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G'Day Blokes,

I am just pulling down a Superliner 500 HP V8 for a friend. It's run 2 big end bearings on the crank, and generaly made a mess of the engine. I have heard that the V8 has a lot of trouble with cranks and was wondering if anyone can tell me if there is anything in the design to make them weak there.

The truck is 1988 manufacture and they are using it to pull a 2 trailer roadtrain (2 tri axle semi trailers with a 2 axle dolly to support the second trailer) with a payload of about 50 ton. It's been going well for several years but has now blown up bigtime. Some of the "experts" they have been talking to are advising to put in a Catterpillar but I know they arn't keen to change unless the Mack is going to give repeated trouble. The block and heads will be apart tomorrow and we are sending them to be crack tested so we have a bit of time to find out more about the service history of this type of engine.

Anyone got any ideas ?

Graham, :)

from Quairading, Western Australia.

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The bloke who drives it is an experianced driver with a lot of years on an "Atkinson" Cummins 350 HP, and before that on "Inters". I think he would keep it spinning nicely but not over reving.

We got the engine out and pulled right down, it was surposed to have been overhauled not long before they bought it, but looking at it it may have only been an in chassis rebuild. It has run the number 4 main bearing and that may (?) be what caused the number 4 & 8 big ends to give out. The rest of the engine is in real good order and no visible cracks in either block or heads but we will get them checked anyway. The mains look like they havn't been disturbed and are a lot more worn than the big ends. The pots and pistons have definatly been replaced, but you could do that without removing the crank.

The main reason I asked about their reliability is out here the V8 doesn't have the same reputation as the Mack six cylinder, and we were wondering if they are well thought of stateside ?

Anyway I will let you all know how it turns out.

Graham :D

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The v8 4-valve cranks are fine but rods and mains need to be done more often then a inline 6.

Pushing a piston on an angle is more work then up and down. the way i did it was at 300 thousand miles on a 4-valve.

150,000 on a 2-valve they were the ones for weak lower ends. my way of being sure

Also doing rods and not mains was a bad idea on the other owner.

The crank dose not need to come out for mains.


Thanks for hearing me out.

You can have the soap box now---------JIM

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Thanks fellers,

I think the owners will keep it original. I was talking to Roger (one of the brothers that own it) and he was telling me the late model Scania they hired to finnish their carting didn't have the power of the "old Mack"even though it is surposed to be bigger. They quite like the truck and have been happy with the performance of the engine, right up until the bang.

When something like this happens you always end up with all the "experts" giving "usefull" :angry: advice and there is a bit of a cloud over V8 performance out here, but no one can tell me what is wrong with them. It sounds like not much as long as you do your maintainance right (and these blokes do) and drive them right.

I will let you all know how it turns out,

Graham :D

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  • 3 weeks later...


Just got back from the easter break to the news that the block has been condemned by the expert.

Cracks radiating out from the cylinder recess to the head studs, the fellow who checked it said its not uncommon and not advisable to use it. Sounds like $$$$$$$

He recons one of the heads has a small crack too !

They have found another engine, but it needs doing up as well, so I don't know which way they will jump.

Have you blokes heard of them doing this in the U.S. or Canada ?

OH well, back to the old drawing board.

I will keep you posted


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