Measuring stroke

baghall Ben Hal Outlaw Bushranger

1,021 posts · joined Jan 2010 · 7 Sep 2010, 8:13 pm

#800977

Can anyone tell me how i could measure the stroke of a crank that is not in an engine atm. I have a set of pistons and cylinders and want to work out the capacity of an engine.
Pistons are 94s but have no idea what the crank is.

68 Baja - It's a growing pain!
58 Baja ute - and the pain spreads!
85 T3 Kombi - still growing
89 T3 Kombi - parts car

waveman1500 Also rides a Honda

1,346 posts · joined Dec 2009 · 7 Sep 2010, 8:34 pm

#800981

The stroke is twice the distance between the centres of the main bearing and the big end bearing, measured radially.

1972 VW S-Bug - For Sale!
1968-onwards Beetle panels and glass for sale

baghall Ben Hal Outlaw Bushranger

1,021 posts · joined Jan 2010 · 7 Sep 2010, 10:38 pm

#801017

Thanks for that waveman. That's what I thought but had been told by a mechanic that I could only measure it set in a block.

68 Baja - It's a growing pain!
58 Baja ute - and the pain spreads!
85 T3 Kombi - still growing
89 T3 Kombi - parts car

waveman1500 Also rides a Honda

1,346 posts · joined Dec 2009 · 7 Sep 2010, 11:25 pm

#801026

baghall wrote:Thanks for that waveman. That's what I thought but had been told by a mechanic that I could only measure it set in a block.

Well, it would be a lot more accurate to measure it with a complete rotating bottom end, because then you can measure the actual stroke of the piston up and down the bore. This is much easier to do.

1972 VW S-Bug - For Sale!
1968-onwards Beetle panels and glass for sale

baghall Ben Hal Outlaw Bushranger

1,021 posts · joined Jan 2010 · 8 Sep 2010, 7:53 am

#801047

Problem is I would need to pull down an engine to do that. The crank was given to me with the piston set none of them attached to an engine block. I just want some idea before I begin pulling down an engine so I can make some decisions over which engine I will be putting them in. Thanks for info.

68 Baja - It's a growing pain!
58 Baja ute - and the pain spreads!
85 T3 Kombi - still growing
89 T3 Kombi - parts car

Phil74Camper Head in the Clouds

2,703 posts · joined Aug 2002 · 8 Sep 2010, 8:22 am

#801053

Aftermarket cranks sometimes have the stroke punched or cast onto the crank web in small numbers somewhere.

If not it's reasonablly easy to measure, thanks to the fact that VW cranks lay flat.

Get a sheet of A3 paper and lay it on your bench, and lay the crank flat on top. Get a metal set square and a sharp pencil. Put the set square on the paper and place against the outer faces of each of the big end journals. Mark the paper - you are dropping a line directly downwards to the paper.

Now do the same with the inner faces of the four big ends. You should now have eight marks on the paper, indicating the inner and outer points of each journal. Carefully rule four lines lengthways, between the two outer points on one side, the two inners on one side, the two inners on the other side, and the two outers on the other side.

Now measure acrossways to get the stroke. Measure between the two outer lines, then between the two inner lines, and average the result. That's the stroke.

You can cross-check by measuring from the outer line on one side, to the inner line on the other side - and vice versa.

This won't be to aircraft or space shuttle tolerances of course, but if you're careful you should get an answer to the nearest mm.