The Stovebolt Site Forums The Shop Area Engine Shop Should I line bore the mains during a rebuild?

I'm going to have a '57 261 rebuilt and I'm trying to get 3 quotes for doing the machine work on the block. The engine was non-running when I got it from fellow forum member HevyHauler so I don't know what the previous running condition was like. It looks to be in decent shape but it's going to need a full rebuild.

One machinist recommends having the block line bored to ensure the crank won't need shimming when it comes back from the crank grinder. He says there is no easy way to check the line bore until final assembly so he wants to go ahead and line bore it during the initial machining process. When I disassembled the engine, there were no shims found on the main caps so it must have been OK at some point. I don't think I can reliably check existing clearances since the bearings and crank journels show some wear. Does anyone know what the likelyhood of requiring line boring really is on these old engines? I want to do this project right but I also want to be sure I'm not needlessly paying for the machinist's new shop equipment.

Thanks,

you would most likely be all right but I think your last sentence answered it best. "I want to do this project right....."

Spend the money now and do it right so that when its together you never wish you had done it every time the engine has a hic-up

You should not have to line bore the block unless the maincaps have been changes or they have been machined on themating face.
I got a quation for the machinist, if you can't check it until final assembly, how does he know it needs it? And how does he know how much it will need? I think I would pass on that machinist, it doesn't sound like he really knows about these old engines.

ijust rebuilt a 60 235 it had no shims at tear down. when putting it back together i had one tight main that only required a .001 shim while not bad it only cost about 100 bucks to line hone.
but at the same time these old engines dont have a real good way of lining up the main caps some tapping side to side while torquing
the bolt helps. philip

Align boring is usually reserved for something someone is going to be putting a large sum of money into. I have a machinist friend that does a lot of rebuilds. and even builds race engines for the local IMCA drivers in this area, and align boring is done very rarely, even on the big horse engines for the track. He rebuilt my 230 in the 64' and we didn't have it align bored, and I'm VERY happy with the way it's turned out. Made it's first real road trip last week down to OKC, and it ran perfectly.
Longbox said it best, you might want to do some more homework about who you want to do your build. Just my .02.

I read one time line boring is a bad thing and should be avoided.
They claimed it puts the motor out of square.
Here is a reference http://www.aa1car.com/library/2003/eb100338.htm

I didn't know you could align-bore a 'bolt. The 235 main bearing housings each have a different inside diameter. Is the 261 different in this regard??

They are the same. So the way it was explained to me by the machinist was that because of the stepped main journel sizes, you can't easily run a straight edge down the journels and determine if they are out from centerline. The mains can be line bored but it requires setup changes for each journel. It takes more time to bore one of these compared to say a SBC and that means extra $$. He said the only way to ensure the centerline is true is to just line bore it regardless. He builds mostly race engines and this technique is pretty standard for race applications. He also builds standard engines but seems to trickle down knowledge he learns on the race stuff to the regular builds too. He also said if I don't want to do it, we can take the chance and assemble it with the newly reground crank and see how it goes together. The risk is that the crank might need to be shimmed to keep clearances in spec. I've never had an engine line bored before but from checking around, it seems to be somewhat more popular to do now days.

Well hellow Ed nice to see you have made it here

Give Bud a call at Bud's Machine Shop in Lakewood, WA. (253)588-2837 very good shop.

Thanks for the tip Grant. I'll add them to the list.

I think I had it done to the 57 235 in my 37,I hope i did not waste any money doing it. Jeff

See if your machinist can follow these directions. 1--put the new main bearings in the block and caps and WITHOUT the rear oil seal. 2--lightly oil with 30wt, NOT Lubriplate. 3--lay crank in and torque caps to spec. 4--if the crank now turns freely with no hard spots then it does not need align boring (most shops align HONE if not way off). This should take no more than a half hour compared to several hours to face off the caps, install and torque, set up the boring jig, etc.

Align honing is an excellent process to do in place of align boring especially if the engine is only slightly modified. Many high end performance shops that align bore also perform the align honing step to match up the bearing clearances for proper oil flow.

I've decided to keep cost down, quality up, and have some fun so I'm going to do all the check and assembly work myself and just use the machinist for machine work. I'll pre assemble the crank and bearings and check with plasti-gauge to see how it looks for consistency between main bores. If any mains are out of round or out of tolerance then I'll have them align bored. I don't believe honing is an option because of the varied main diameters. At least not with my machinist's equipment.

I could be wrong but I don't believe the main bore diameters are different. The cam bearings are but I think the mains are the same.