TOPIC: Cylinder bore measurement

Everything I read about these old 1350's suggest that it is common for the cylinders to get out of round. Any of you folks have a simple way of checking this, or do I need a special set of tools like this: www.amazon.com/Anytime-Tools-16-PRECISION-TELESCOPIC/dp/B000I8NDAS

I am somewhat concerned that the "good" 1350 I have may have oversize cylinders, but don't know how to tell other than measuring them somehow. I can't see any markings on any of the pistons. Wouldn't oversize notation be somewhere on an oversize piston, or are there times that isn't the case?

The reason I'm concerned is it is obvious this powerhead has been opened up before (the salty hadn't). Of course, I have no idea why, it just makes me suspicious. I would hate to put out good money for new rings and then find out they're the wrong size!

Any tips, suggestions, or help would be very much appreciated. Thanks!

Frank

the tools you posted a link to will only re-create the measurement from the inside of the bore. you'll still need a precision way to measure those tools...

i'd take a set of calipers to 'em. you don't need the fancy ones. the $3 set from harbor frieght should be sufficient for what you're doing. those calipers can do both outside and inside measurements. i'd use 'em to check the bore diameter in several places. this isn't the most accurate way to do things, but you will get an idea as to what the overall bore size is, and whether or not the cylider's out of round (by seeing how much the measurement varies). also, i didn't know how to read the calipers with no dial on them, but i googled that and the answer was readily available.

Frank I have some Micrometers you can use with those tools to check the measurement.

I have precision calipers to measure those tools I posted. I didn't think just a caliper measurement at the top of the cylinder would tell me it the cylinder was out of round. If that's the deal, it's easy to do, and I'll give it a whirl tonight with my calipers. Thanks!

Frank

Frank I think you still will need those Bore guages to get a good reading on the variation in the bore where the piston rides.. and a set of good calipers or Micrometer to read the variation.. I havent done it on an engine, but I dont see how you would measure with just calipers....

you can use the calipers to check the out of round at the top. if there's a step in the cylinder wall, you'll need a feeler gauge too. use the feeler gauge between the caliper jaw and the cylinder wall and then do a little math. it won't tell you about the shape of things further down the cylinder wall though.

like i said, this isn't the way i'd measure things if you need the utmost of accuracy. but, if you just want a general idea and you have these tools on hand, this should work. if you measure the bore in several places and all of the measurements are identical, i'd say you're safe in thinking that the cylider's not out of round. if they're .030" different, it's obviously out. if the measurement is close, then yeah, you'll need more precision tooling to make the determination.

you may still need more accurate tooling to determine cylinder I.D. I'm not sure how much bigger they bore the cylinders on a boat motor when they oversize them. on cars they step things in .010" increments. a decent caliper should be able to pick up on a difference of that size.

again, if the calipers show anything questionable then step up to more accurate tools. if you hace micrometers at your disposal and you know how to use them properly, go for that instead.

These look decent, for about the same money, and are titanium-coated!

www.amazon.com/Anytime-Titanium-Coated-TELESCOPING-Precision/dp/B004CZ4QOU/ref=cm_cr_pr_sims_t

I'd say that since you have a good pair of vernier calipers, that you should be able to get a darn good idea of the cylinder out-of-roundness, taper, and size using those telescoping bore gages.

It does take a bit to get the 'feel' of how those gages work when measuring a cylinder, but with a little practice it's pretty easy.

And you've got at least 12 bores to practice on!

One thing you can do is measure out a few of your pistons, if they come out the same size you can pick one to "test" fit the cylinders in both blocks. You'll know right away if you have an oversize hole, since a standard-size piston is gonna rattle around like crazy in an O.S. hole.

Or just measure out all the pistons/test fit every hole in both blocks, just to see what happens. I'd say it'd be extremely coincidental and just doggone unlikely to find 2 motors with all oversize pistons.

BTW any oversized pistons should have the size stamped into the large flat face of the piston. You might have to clean carbon deposits off the piston to be able to see the markings. I've never seen any O.S. pistons not marked, but I suppose anything's possible over the years!

HTH & Have Fun!..........ed

Man o man, ya gotta love Amazon. I am a "Prime" member, so anything they stock I get free shipping, and can buy with one click. A lot of weird stuff they sell comes from different suppliers, and that charges freight, but not these tools. Hmmm.

Ya know, in my experince, even with a bit of carbon coating, one can usually see indentations that suggest letters or numbers. Not on these babies. I haven't had a chance to de-carbon the tops yet, and hope to get there maybe by week's end. This job of mine sure cuts into my fun...

I don't have any pistons off yet. Instead I have not only a crazy job, but a puppy (grrrrr!) that is taking time away from the shop when I am home. Not sure what to do next! All I can tell you is I want to get one 1350 built and on my little boat!

Thanks Ed, I will keep y'all informed.

Frank

Frank,the question has been well answered by many but here is another way to check for cyl taper. Take an old or new ring, whatever you have handy. Insert the ring in the cyl and level it with a piston, measure the ring end gap. Move the ring down, measure again, move it down again and measure. You can measure with a simple feeler gauge. If the cyl is tapered you will see a wider ring gap at the worn section. If your end gap is the same your cyl is not tapered. This method takes all the math out of the equation and you are using the ring as a measuring tool.

Gee, great idea Dave! I kinda get it, let me think about it. Been very busy at work and with our new "project" (puppy), but hope to spend some time in the shop within the next few days. Thanks!

Frank

I doubt they are oversized if they are not stamped. If in doubt measure the pistons with a caliper. They should measure 2 7/8ths inch for STD pistons.

My thoughts exactly. I sprayed carb cleaner on the top of one this a.m., and brake cleaner on another. Gonna let them sit a bit, then see if I can get some of the thin layer of carbon off with a toothbrush.

Thanks!

Frank