Thinking about doing a rebuild on my 235 or a 261 inline 6 Chevy. I had talked to one of the guys that is good on these old engines and he said I should have a line bore job done. Is this enough better than just a standard bore job to justify the added expence? This car will be driven a lot so I want it to be done right. Thanks for your input. Later, Dick
Line bore would be for the mains unless their is some thing wrong you should not need to do a line bore take that block to a good machine shop and they will make sure every thing is good.
I understood what a line bore was, but questioned if doing a line bore would benefit me on the engine rebuild. Thanks for the responce. Later, Dick
Unless the engine has experienced an overheated or spun main bearing in its past. You should not require a line bore for a stock rebuild. These engines are not known for that type of problem. It will require hardened exhaust seats for a "working" engine. A "parade" engine can get by with a standard valve job and some lead additive.
He is talking aboput getting your main bearing saddles in a perfect line. It will free up a little torque if it is done right and they were not already in alignment.
I say do it. When assembling my 54 235 after machining the crank wouldn't spin. I had to return it for a line bore. All was fine after that. Dom
Thanks again for your advice. The hardened valve seats are a must as this car is going to be driven. Later, Dick
Best advice so far. An align hone is sometimes called for- let the machine shop check it first. If the main bores are not square with each other (in alignment) or are improperly sized for proper bearing crush, a properly-done align hone will correct it. Downside, and why I don't have it done unless necessary, is it moves the crank slightly closer to the cam, with timing chain slack or tighter clearance if it has timing gears. Not something you want to just say yes or no, check it first, don't let them just check it off on the work order to jack the price up
Good advise, with a six I think you have a gear driven cam, and if your shops a little off, align bore will mess up centers. As said, check it, maybe hone, but try not to bore it. Also, try not to take too much off the deck of block, and head surface. Just enough to clean them up. Do pay for a balance, big difference,
This is an if you need it thing like surfaceing a head. I like boring better honing. Boring done right will not move the center line of the crank much while a hone will move the center line closer to the cam.
There are 2 ways to save money when building an engine, "half fast" and "half assed". Building an engine "half fast" will save you money because it won't cost you an arm and a leg for all those fancy speed parts but won't cost you money in the long run because it was built right. Building an engine "half assed" is a recipe for disaster that will cost you in the long run. Don't be pennies wise and dollars foolish. Align boring doesn't cost that much. Just get it done!
These engines cannot be align honed, only line bored, since all 4 of the mains housing bores are about .100 larger than the next one in line. GMC's are the same, 4 different size main housing bores.
If you have a 261 for example, here are the specs and why it can't be align honed. #1 2.6835-2.6845 #2 2.7145-2.7155 #3 2.7455-2.7465 #4 2.7765-2.7775
Did NOT know that- they also did that on the early Chevrolet 4 (1928 and prior) and it's ANNOYING at best!!!
ANY method other than sleeving the saddles will move the centerline up. The ammount depends on how much you have to take off the caps to get it to clean. Like others here have said, you can't hone these engines because of the different diameters of each bore. They could be checked with a stepped test bar but my guess is there aren't many of those left around any more.
How many miles you got on that old motor? More than a 100K? Maybe it has already been rebuilt before? Don't you think that the mains are already in line? Like maybe there is a real good reason why that engine is 60 years old and still running? Let the machine shop true up the mains on some toyotas but leave yours alone.
Heres what I have on the discussion of the " Shim Pack ". Now what I have is that this applies to the 54-55 w/ Dowel Pin type main bearings - UNDER NORMAL CONDITIONS. This would not apply to the 56-62 engines. " Under normal conditions Main Bearings should be assembled with a .004" shim pack on each side between the caps and the block. This should not extend between the bearing parting line surface. Remove shims to give a slight drage, then add 1 of a - .002" shim per side ".
On most engines you can set the bar that It just touches the top of the crank bore and most of the metal will be removed from the cap. With a hone an equal amount will be removed top and bottom.
More than one source has said if a straight (measured) crank turns freely in bearings with correct clearance the main line is straight enough. Makes sense to me. The bores (without inserts) do need to be qualified regarding size, roundess and taper.
I run a GMC Jimmy 302 in my Belly Tanker and the mains are all different sizes. My opinion, DO NOT align bore ! What are you going to do for main bearings ? Some people have advised to align bore, sure, if you can purchase bearings ! You better talk with your machinist and discuss this issue regarding different size main bearings first !
A CMM will make quick work of determining EXACTLY how concentric the main bores are and shouldn't the amount of misalignment be determined before getting out the boring bar? Amazing what is done to make up for a lack of measurement capability.
When you line bore or align hone a block the main bearings are not affected at all, you can use any main bearing just the same as if you didn't line bore or align hone the block. During this process, the housing bores are restored to their factory specs by cutting a few thousandths off of the caps mating surfaces to close the housing bores up so they can be resized just like reconditioning a set of rods. You must be thinking of a VW where the housing bores are actually made larger than they were originally and special OD bearings are required.
If it was line bored what would you do for cam gear play if the crank moves any up down or sideways . JMO if it was in need of line boring Iwould look for another block.
Quote: Originally Posted by Candy-Man I run a GMC Jimmy 302 in my Belly Tanker and the mains are all different sizes. My opinion, DO NOT align bore ! What are you going to do for main bearings ? Some people have advised to align bore, sure, if you can purchase bearings ! You better talk with your machinist and discuss this issue regarding different size main bearings first ! Quote CNC - Dude : When you line bore or align hone a block the main bearings are not affected at all, you can use any main bearing just the same as if you didn't line bore or align hone the block. During this process, the housing bores are restored to their factory specs by cutting a few thousandths off of the caps mating surfaces to close the housing bores up so they can be resized just like reconditioning a set of rods. You must be thinking of a VW where the housing bores are actually made larger than they were originally and special OD bearings are required. Sorry my response should have said "line hone" and not "line bore". However; how would you ever line hone a Jimmy block as the main are different sizes, what would you use to center ? I still maintain, I would not venture into either territory if you did not believe there was an issue, ie: spun bearing..... I must have really messed up my Jimmy block in my Bonneville car !