Can the stroke of an engine be determined without tearing the engine apart? Torn apart or not how do you determine the stroke (what do you measure? In this case the bor
e is known.

 

What is the motor? Not sure of your knowledge but a here are a few STOCK strokes;

302 SBC = 3"
327 SBC = 3.25"
350 SBC = 3.48"
400 SBC = 3.75"

396 BBC = 3.76"
427 BBC = 3.76"
454 BBC = 4"
502 BBC = 4"

Then combination like a 3.75" stroke crank in a 350 (.030 over) makes a 383.

Anyway, to answer your question, you could pull a head and use a dial indicator to measure stroke.

 

Specifications for the crankshaft can usually give you the stroke. Do you have a part number for your crank?

 

An engine's stroke is equal to the distance from the [spindle] centerline of the crankshaft to the center of a rod journal, then multiplied by 2. You should be able to put a scale between a crank journal and an adjacent rod journal and get a pretty good measurement between the centerlines of those two journals. Double that measurement and you have the 'stroke'.

 

Is it possible to measure the distance from BDC to TDC with a rod through a spark plug hole or am I being to simplistic?

 

You probably could. Maybe a piece of stiff but pliable thin wire. Stick it through the plug hole, once at BDC use a marker and mark the wire right where it exits the hole. Then at TDC do the same thing, pull it out and measure the distance between the two marks. A little bubba but could work.

 

I would think that the angle of the spark plug hole would be to great to do this, but, hey, it's worth a try to find out for sure.

I think your best bet would be to use a technique called "guessing". I'll demonstrate how it works, thusly: I am guessing that your engine's stroke is 3.48". It's a pretty easy technique to master, not very accurate, though.

Seriously, though, I would think that the easiest way to get a half-way accurate measurement with as little dis-assembly as possible would be to remove the oil pan, and try to measure the distance from the bottom of the cylinder to the bottom of the piston skirt at TDC with some sort of thin, flexible rod, then do it again at BDC, and figure the difference.

Scott

 

Wishfully simplistic.

 

Oops! I misread the original post..."without tearing the engine apart"...

Only one way I can think of to do that with any accuracy. I've never done it, but it should be possible.

Remove a spark plug where you have the best access to that plug hole. Rotate engine so that the piston in that cylinder is all the way to the bottom of the stroke. [Stick a thin piece of sturdy wire into the plug hole so that it touches the top of the piston while finding the lowest point on that stroke. It doesn't have to be exact.]

{Here's where it gets a little wierd }

Fill that cylinder with water or other fluid till it runs out the spark plug hole. Now fit a piece of vinyl tubing into that plug hole so that it will tightly seal at the threads; only insert it to the depth of the threads. Get a clean little can/tub/bottle and use it to capture the fluid from that cylinder as it is slowly turned to TDC. You can over-rotated the crank, if you want, as it will only expel what fluid is in the cylinder. Do this slowly so you don't blow the tubing out of the plug hole.

Now, you just need to measure the amount of fluid in that container. Once you know the volume, it's a simple math problem (since you know the bore dimension) to calculate the stroke required to yield that cylindrical volume.

I can't think of another way to do it, without removing [at least] the oil pan.

Although this method sounds a little strange, it shouldn't be that much trouble and a little excess water in the cylinder shouldn't do more than cause a puff of steam out the exhaust when you start it back up.