"overbore"

[Jorn J.]

Hi Friends
How much is possible to "overbore" a 283 Block with no. 3756519 ?
My "engineshop" here in Denmark says 0.60 and some other says 1.25

Regards Jorn

[Stuart F.]

Re: "overbore"

I think you mean .125" or 1/8". That was common back in the day (50's and 60's) which would give you 301 cu in. (5 litre).

Stu Fox

[Tom P.]

Re: "overbore"

Hi Friends
How much is possible to "overbore" a 283 Block with no. 3756519 ?
My "engineshop" here in Denmark says 0.60 and some other says 1.25

Regards Jorn

Not all engines can be bored the same amount, not even blocks with the same casting number. Cast parts, such as engine blocks, are made up from several sand molds that are put together and then the molten metal is poured into the assembled mold. During the casting process, some of the mold parts may move around or shift (commonly called core shift) during the process. As a result, some parts of the cast part, such as the cylinders may be thicker on one side than they are on the other side. Consequently, it may not be possible to bore one block as much as another block, even though the blocks have the same casting number and were cast at the same foundry.
One of the best methods of testing the thickness of cylinder walls of a block is to do a sonic check and not all machine shops have the equipment to do this.

[Joe C.]

Re: "overbore"

Not all engines can be bored the same amount, not even blocks with the same casting number. Cast parts, such as engine blocks, are made up from several sand molds that are put together and then the molten metal is poured into the assembled mold. During the casting process, some of the mold parts may move around or shift (commonly called core shift) during the process. As a result, some parts of the cast part, such as the cylinders may be thicker on one side than they are on the other side. Consequently, it may not be possible to bore one block as much as another block, even though the blocks have the same casting number and were cast at the same foundry.
One of the best methods of testing the thickness of cylinder walls of a block is to do a sonic check and not all machine shops have the equipment to do this.

I agree with Tom. Additionally, as a rule, 283 blocks have been known to have thicker cylinder walls than later blocks such as those used for 327/350/400 engines, whose maximum overbore is generally considered to be .060" (ONLY if your block has consistent cylinder wall thickness). The reason for this, is that the water jacket shape relative to the bore was changed with the 327 blocks ("870").

If your cylinder walls are too thin, your engine will not produce maximum power because the cylinder walls will flex. There are rules of thumb for advisable wall thickness, and the values are different for the minor thrust wall, the major thrust wall, and the non thrust walls.

[Robert J.]

Re: "overbore"

I had to sleeve my 265 block. Sometimes you have no choice...

[William C.]

Re: "overbore"

up to .060 is generally safe, to go beyond that, I'd have each cylinder sonic tested for thickness and uniformity of the casting before going more. As mentioned. sleeving all cylinders back to stock bore is also (although pricey) a possibility.

[Jorn J.]

Re: "overbore"

Okay Guys
Then I don't have to be so nervous about 0.40
Thanks for the answers.
Regards Jorn

[William C.]

Re: "overbore"

.040 over should last the rest of your lifetime.

[Jorn J.]

Re: "overbore"

William I hope your right

Jorn