Dart BBC main bore repair, oversize bearings available?

[coolchevy]

Just got shocking truth from my machine shop guy who works on my Dart BigM block (632ci) to fit new Callies crank that the previous machine shop butchered up the main bore badly when they fixed main bore 2 years ago when a bearing spun.

the only way to fix it would be a oversize main bore, i would need some race bearings which have a thicker shell by about 0.01" or 0.25mm to get bore straight and clean again.

anybody knows who makes such an animal????

it is rather urgent or 2012 season is already seriously endangered

[avengerengines]

I saved a Dart Little M block by using a Sealed Power .020 over and .010 under. I don't know if they make it for a big block but it would be worth looking into.

[MotionMachine]

I've done a couple of them also. Just remember you'll need to make some +.020" main rings if you use a 2" bar for boring or decking. The brgs I used were also only available in a -.010" crank size.

[coolchevy]

-010 undersize would mean having to grind a brand new Callies Magnum crank, that would give me physical pain. Even more pain to scrap the otherwise perfect block which has a lot of machining and hardbloc filling in it. (twin turbo Methanol)

Oh god, there must be viable solutions !

[avengerengines]

-010 undersize would mean having to grind a brand new Callies Magnum crank, that would give me physical pain. Even more pain to scrap the otherwise perfect block which has a lot of machining and hardbloc filling in it. (twin turbo Methanol)

Oh god, there must be viable solutions !

It's a no win situation. If you grind the crank .010 and damage it later there are no .020 bearings, yet it's hard to just scrap the block. Do you put it together and take your chances, or get another expensive block? What to do, what to do?

[user-z68766209]

Spray weld the 2 saddles and buy 2 new caps and and do it right.

[TMSJoe]

Not sure I would do this for a customer but I would do my own block this way. Get the block honed perfect @ +.010 as an example. Then take .005 shim stock and place the shim under all the bearings during assembly. They make bearing spacers for 350 blocks and 283 cranks. They are basically a second bearing placed under the primary bearing. My 377 in my wagon was like that and I towed my car to the races with it and drove it for 11 years.

[kirkwoodken]

Seems to me your problem should be addressed by AT LEAST one bearing company. I have a block that is presently .0003" over the high side of tolerance. .001" under bearings have too much clearance with the virgin crank I have. Choosing a base material for bearings that is .0025" and .0050" thicker does NOT seem like a huge deal. Someone on this forum MUST have some pull with a bearing supplier. I've not been successful getting the backings plated at local plating companies.

[kirkwoodken]

[quote="TMSJoe"]Not sure I would do this for a customer but I would do my own block this way. Get the block honed perfect @ +.010 as an example. Then take .005 shim stock and place the shim under all the bearings during assembly. They make bearing spacers for 350 blocks and 283 cranks. They are basically a second bearing placed under the primary bearing. My 377 in my wagon was like that and I towed my car to the races with it and drove it for 11 years.[/quote]

I would bet many have done this, including myself. When you are a toolmaker by trade, you shim a lot of stuff with no catastrophic results. That's why they make shim stock. Still, I'd like bearings unshimmed.

[coolchevy]

what happened ist that they main bored from both sides, thus, the inner three bores are not only angled to each other, they also took more material out of the block then off the saddles. Complete inept idiots. No wonder my crank broke later on.

so the front and rear bore lines up with but the inner three are all over the place, the inners are out as much as 0.25mm, up and down as well as left and right

to make matters worse, they ground saddles without any comprehension and fear, so much down that they were no longer indexed at the side of the block and just held by the main bolts. So Hans, the new machine shop guy who usuall does all my blocks, had to electrolytically add material to both ends until the fit snuggly inside block, then he checked main bore and he almost fell off chair in disbelieve. I went to the other shop just because they had closed 3 weeks for summer vacation, been there 25 years and no issue.....just one time i go somewhere else and disaster strikes.

am I pissed, you guess. First my Bryant crank broke at journal #1 because these fools have ground my journal radii away, now that. Luckily it broke after a full pass in the tow lane and not during the pass at 8000 rpm, that could have cause some grief when engine seizes up at 170 mph.........

Chris Straub is trying to fix me up with a King bearing, other then that I am not sure if spray welding is a good choice on an cast iron block? Has anybody done that to a Dart block?

[avengerengines]

Cast iron spray will work. Why did he bore it on the first repair?

[Baprace]

Found a part number for .020 over size bearing shells, the only problem is the rear bearing is standard over size, it's a old Clevite number MS 1748-10 , the 4 shells are marked MS 3123 and the rear is MS 2404. it appears the set can be had in undersize bearing diameter also with a listing for .010 and .020. Hope that helps

[Alan Roehrich]

Spray weld it and fix the main bores the right way, and be done with it, or buy another block. Otherwise, you're just wasting time and money. Of course, it is your time and money.

[coolchevy]

I know on Monday if it could be fixed. If we move the crank centerline up into the block by 0.008" we could get a clean bore. It is at a machine shop right now which can bore up to 1m in length using a laser to find crank bore centerline.

I might have to turn pistons crowns by same amount, compression increase doesn't bother me as I am rather low for a methanol twin turbo engine anyway. I moved from Aluminum rods to Callies Ultra billet steel rods so clearance to cam ain't an issue and if only need a little thicker idler pulley on my belt drive. If it works as planned I know on Monday..........

spray welding was declined by everyone who saw damage so far..........

[pamotorman]

Not sure I would do this for a customer but I would do my own block this way. Get the block honed perfect @ +.010 as an example. Then take .005 shim stock and place the shim under all the bearings during assembly. They make bearing spacers for 350 blocks and 283 cranks. They are basically a second bearing placed under the primary bearing. My 377 in my wagon was like that and I towed my car to the races with it and drove it for 11 years.

I would bet many have done this, including myself. When you are a toolmaker by trade, you shim a lot of stuff with no catastrophic results. That's why they make shim stock. Still, I'd like bearings unshimmed.

don't forget to put a hole in the shim stock for the oil flow. i have used steel shim stock for this purpose.