How to determine the displacement of an Engine

[Tom Oxner]

I have an engine that was from the shop of the late Grady Clay. It is a twin plug engine built on a 2.0 liter case. It has biral cylinders. It is a type 901/14 case with # 3280982. I would like to determine the displacement of the engine. Is there a way to determine the actual bore and stroke of an engine without removing the heads? Thanks.

Tom

[Arlo911]

Maybe filling one cilinder at BDC with fluid should give you the displacement, multiply by six?

[sugarwood]

Submerge it in a bathtub like Archimedes?

[Otter74]

Probably using fluid, but since displacement is swept volume you'll need to measure a cylinder (through the spark plug hole, I imagine) at BDC as well as at TDC and take the difference.

[RWebb]

use ATF and use a burette

Grady kept ring binders on everything - if you can find the one for that motor

[dannobee]

Burette is a good idea. But I'd use windshield washer fluid instead. And you'll need to back the rocker arms off first, otherwise the fluid will run out the exhaust when the cam opens the exhaust valve before bdc. Put the cylinder up to TDC on the firing stroke (verify with the dist rotor), rotate the engine on the stand until the spark plug hole is pointing straight up, then use your burette or syringe to fill up the cylinder, noting how much fluid you used. Then turn the crank 180 degrees and add more fluid until it's full again. The difference between the two is the displacement of one cylinder. Actual compression ratio will be the second number divided by the first number. Turn the engine back over to let the washer fluid drain out.

[otto_kretschmer]

Originally Posted by RWebb

use ATF and use a burette

Grady kept ring binders on everything - if you can find the one for that motor

probably would need something thicker that won't seep past the rings

grease would be ideal

[otto_kretschmer]

grease is probably too thick

maybe corn syrup

[Tom Oxner]

I may try the ATF and a burette. The fluid needs to be thick enough not to seep past the rings, but thin enough to remove easily. I had heard that Grady kept detailed records, but I am sure they are long gone by now. Thanks for your suggestions.

BTW, since the engine has biral cylinders, were the biral cylinders available on the 2.0 liter engines or just on the 2.2 and 2.4?

Tom

[Steve Marshall]

I'm in the same boat on a 2.4. I would like to know the compression ratio as well. Thanks for the comment about swept volume. I did not realize that's how it calculated. Is that a Porsche thing or are all displacements based on swept volume? This will also be helpful for calculating compression ratio.

[dannobee]

If you've ever worked on water cooled engines, you'd know that rings will seal adequately enough for rust to form in the cylinders; it'll stay there for quite a long time. Certainly long enough to take a couple of volume measurements. ATF or god forbid, corn syrup, is a recipe for a big mess. And a lot of smoke on startup.

[otto_kretschmer]

I would do a leak down to see if the rings are in good shape and if they are I would put on cylinder at BDC and use a graduated cylinder and motor oil. You will get the quench volume along with the swept volume so you will have to drain the oil and repeat this with the cylinder at TDC and subtract.

another thought.. put the oil in your freezer for a couple hours and use it cold

[Otter74]

Originally Posted by Steve Marshall

I'm in the same boat on a 2.4. I would like to know the compression ratio as well. Thanks for the comment about swept volume. I did not realize that's how it calculated. Is that a Porsche thing or are all displacements based on swept volume? This will also be helpful for calculating compression ratio.

Yes, engine displacement is always measured as swept volume of the pistons, and can be calculated solely from bore, stroke and cylinder count. ( (Pi*(bore/2)^2)*stroke)*(cylinder count) ) Compression ratio, as noted in another comment, is a measure of how much a volume of air has been compressed and is therefore the ratio of maximum total cylinder volume to minimum total cylinder volume. This must therefore take the volume of the combustion chamber into account.

[RWebb]

ATF will not induce rust (supposedly)

do it quick to try and prevent it from getting past the rings

oil will be fine if it flows out of the burette ok