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#1
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Scat crank thrust too small
So I am freshening up my 455 from having a cam lobe go flat. All new bearings. Crank is a Scat forged 4.25" stroke. Well upon fitting the new bearings, I see the thrust opening in the crank is about .060" thinner than the bearings. My machine shop ground down the thrust surfaces on the bearings he installed in my engine. BUT, he ground them to the steel backer!!! I don't see any crank damage, Engine only had maybe 3000 street miles on it. But is there thinner thrust bearings a guy can get? Or am I looking at machining the crank? New bearings won't even fit in the lobes.
The crank PN is Scat 4-455P-4250-6700-2200 Last edited by zippy; 03-16-2022 at 06:55 PM. |
#2
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So you have a 4.250” stroke crank, what size are the mains, 3.00” or 3.250”?
Cranks with a 3.00” main use a thrust bearing that is 1.135” in width, cranks with a 3.250” main use a thrust bearing that is 1.195” wide, so there’s your .060”!
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I do stuff for reasons. |
The Following User Says Thank You to 25stevem For This Useful Post: | ||
#3
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It is 3.25" mains. 455. But the thrust is 1.135" wide on the Scat Crank
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#4
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Do you still have your old main bearings?
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I do stuff for reasons. |
#5
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Yes I do. But the thrust surfaces were ground down to fit the crank by the builder, whom I'm never using again. He had to grind .030 off each side of the bearings. So much that it's to the steel backer of the thrust surface Now I dunno if this a messed up scat crank or what.
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#6
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an average shop SHOULD be able to FIX your crank without too much issue....yeah it sux but that's what it is.
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#7
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Sounds like a 3.00" crank got mixed into the 3.25" main line when they were grinding thrust surfaces. At least your crank is too narrow instead of too wide. Just need to find a highly recommended shop with a crank grinder and someone who actually knows how to use it. They should be able to grind that just right for you and you won't have to use jacked-up bearings in it anymore. I have tweaked the thrust faces on the bearings with a surface plate and wet/dry paper to get the exact thrust clearance I want. But typically no more than .003-.005" off the faces.
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The Following User Says Thank You to mgarblik For This Useful Post: | ||
#8
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Ya. That's what I'm thinking too. And I guess it'll have to get rebalanced too as they have to open up the counterweight spacing there too.
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#9
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Wow that sucks did you guys we the thread about the crank w a hole in it brand new eBay / China part 4.50 stroke. Seems China isn’t doing such a great job these days. At least yours is fixable. Kinda rethinking my purchase of a stroker set up right now though.
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Happiness is just a turbocharger away! 960 HP @ 11 psi, 9.70 at 146. Iron heads, iron stock 2 bolt block , stock crank, 9 years haven't even changed a spark plug! selling turbos and turbo related parts since 2005! |
#10
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Who did you buy the crank from?Did you try going back to them to handle the deal?I would not touch the crank until you talk to them or SCAT!They were just sold and im told things are a little messed up right now.In the past I have had good luck with their products.Tom
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#11
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Quote:
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#12
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The Following User Says Thank You to mgarblik For This Useful Post: | ||
#13
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Good crank shops can do wonder with forged cranks.Just had the thrust welded up,turned and reheat treated at a local shop here.Tom
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#14
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Quote:
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“It takes considerable knowledge just to realize the extent of your own ignorance.” Dr. Thomas Sowell |
#15
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So, I've been in contact with the shop who assembled the bottom end like this and ground the bearings down. He says not a problem. Just needs crank, bearings and main cap. My dilemma tho is, he, or someone at his shop, ground the thrusts to steel, then assembled and shipped off to me. Now do I trust this shop to make it right? Or do I bite the bullet and pay another shop to do it? Also, everything has been balanced before. Looks like probably going to have to take .010" off each inside of counterweights at the thrust bearing at least. It's about .015" narrower than the bearing thrust surfaces right now. 1.1795" between counterweights. Is this going to throw my balance off enough to warrant a rebalance?
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#16
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I'd pick a new shop.....
Spend the extra cash now or you will be wondering about it FOREVER.....
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#17
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For the record, I will be doing my own assembly and measuring everything. This has been the first time I ever had someone assemble a bottom end for me. Prob 8-10 engines in my life with no problems with me checking everything
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The Following User Says Thank You to zippy For This Useful Post: | ||
#18
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I have seen the thrust bearing ground when using Scat cranks before and they last and last. I doubt it was incompetence, the "thrust" surface doesn't get much wear at all if everything is right.
Scat, like Eagle, had a machine shop in the US and fixed the forgings made in Asia on old American made equipment.
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"The Future Belongs to those who are STILL Willing to get their Hands Dirty" .. my Grandfather |
#19
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#20
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Sounds like a hack job to me. Why wouldn’t you (the shop) just fix it right rather than band aid it And even IF they were going to band aid it, why wouldn’t they ask you if that’s what you want them to do. I know I wouldn’t let them do it again Id have a better shop do it, if you know of anyone better. Sometimes it’s hard to find good machine shops especially these days .
When your buzzing that thing high up in the revs you’ll be happy you did .
__________________
Happiness is just a turbocharger away! 960 HP @ 11 psi, 9.70 at 146. Iron heads, iron stock 2 bolt block , stock crank, 9 years haven't even changed a spark plug! selling turbos and turbo related parts since 2005! |
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