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Posted by: knuckledrgr914 Apr 25 2009, 08:25 AM

I have a 1.7l '70 914 and I am looking at purchasing some new 96mm cylinders/pistons for it. I am told the cylinders/pistons will work if my motor is a stock 66mm stroke. How can I tell the stroke of my motor?

Thanks,
Brad

Posted by: Dave_Darling Apr 25 2009, 08:44 AM

Pop the heads off and measure how far up and down the pistons move. That's the least-invasive way I can think of...

--DD

Posted by: brant Apr 25 2009, 09:17 AM

has your motor been rebuilt previously?
do you think it is still a stock 1.7?

I'm guessing you have stock stroke unless you have reason to believe someone put a 2.0 crank into your motor in the past?

even if your motor had been rebuilt, its not likely that someone changed the stroke. Usually bore is changed (cheaper) instead of stroke

if you post a picture of your piston (disassembled) and the wrist pin location on the piston people can tell you which length of rod/crank you have. you can even measure the wrist pin height and post that

Posted by: McMark Apr 25 2009, 11:22 AM

Look at the wrist pin side of your connecting rod. If it's big and square, you've got a 66. If it's rounded off, you've got a 71. Unless of course, it's not one of the two stock cranks.

Posted by: Todd Enlund Apr 25 2009, 01:26 PM

Use a chopstick in the spark plug hole...

Posted by: Todd Enlund Apr 25 2009, 01:27 PM

There are two sets of cylinders for 66mm stroke, so the stroke alone won't give you the answer. The head registers are different.

Posted by: McMark Apr 25 2009, 03:06 PM

Todd, the head registers are an issue, but piston pin height is different between 71 stroke P&C and 66 stroke P&C. So you gotta look at both stroke and heads.

Posted by: knuckledrgr914 Apr 25 2009, 03:22 PM

To answer your question brant, the motor does appear to have been rebuilt in the past. The current size of the pistons and cylinders is 96mm and the numbers on the cam says it replaces those found in a 2.0l... Also, Sorry! I should have meantioned the case is cracked and the motor is completely stripped... There is ready access to all parts. Attached are some pics of meantioned parts. Does this help anyone identify the stroke?

Thanks,
Brad

Posted by: ArtechnikA Apr 25 2009, 03:41 PM

stroke is distance from main bearing centerline to crankthrow centerline times two.

Since you have the crank available, you just need a ruler.

Posted by: Todd Enlund Apr 25 2009, 03:53 PM

Yeah, that's why I mentioned "cylinders" and "stroke alone won't give you the answer"... I guess between all of us we covered the bases...


Those rods are for the 66mm crank. Disassembled, you can just measure the stroke directly... but also, the rod journals on a 66mm crank are 55mm, while they are 50mm on a 71mm crank.

Again, make sure that the cylinders are the correct ones for your heads, or you may be facing some additional machine work.

Posted by: knuckledrgr914 Apr 25 2009, 03:53 PM

Thanks ArtechnickA! I have some calipers so I should be able to measure it... The only problem is I am not sure what the main bearing and the crankthrow are Based on the attached picture, could you dumb it way down for me?

Thanks,
Brad

Posted by: ArtechnikA Apr 25 2009, 04:00 PM

red line - crankshaft centerline
green line crank throw line


Attached image(s)

Posted by: knuckledrgr914 Apr 25 2009, 04:03 PM

Thanks Todd! I believe the PO had the 1.7l heads worked to fit the 96mm cylinders, but I think I may throw some 1.8l heads on the motor and it should work just fine?!? At least from what I have read...

Brad

Posted by: knuckledrgr914 Apr 25 2009, 04:12 PM

Thanks! I appreciate the help... I will get to measuring and see what I find.

Bra

Posted by: knuckledrgr914 Apr 25 2009, 04:27 PM

If I measured it right, the crank appears to be 66mm... Would you agree?

Thanks,
Brad

Posted by: McMark Apr 25 2009, 07:29 PM

Those rods are for a 66 stroke crank. If those rods came off that crank, it's a 66.

Posted by: jd74914 Apr 25 2009, 08:17 PM

Bad day removing rings? Sorry, I couldn't resist

Posted by: knuckledrgr914 Apr 26 2009, 08:45 AM

Thanks McMark!



Go ahead jd74914... Laugh at other's misfortunes why don't you!!!

Ya, I guess I could have cleaned up my backdrop a tad. Thanks for pointing it out

Brad