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> How can I tell the stroke of my motor?
knuckledrgr914
post Apr 25 2009, 08:25 AM
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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
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Dave_Darling
post Apr 25 2009, 08:44 AM
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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
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brant
post Apr 25 2009, 09:17 AM
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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
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McMark
post Apr 25 2009, 11:22 AM
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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.
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Todd Enlund
post Apr 25 2009, 01:26 PM
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QUOTE(Dave_Darling @ Apr 25 2009, 07:44 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

Use a chopstick in the spark plug hole...
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Todd Enlund
post Apr 25 2009, 01:27 PM
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QUOTE(knuckledrgr914 @ Apr 25 2009, 07:25 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

There are two sets of cylinders for 66mm stroke, so the stroke alone won't give you the answer. The head registers are different.
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McMark
post Apr 25 2009, 03:06 PM
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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.
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knuckledrgr914
post Apr 25 2009, 03:22 PM
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QUOTE(brant @ Apr 25 2009, 09:17 AM) *

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

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


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

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ArtechnikA
post Apr 25 2009, 03:41 PM
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QUOTE(knuckledrgr914 @ Apr 25 2009, 05:22 PM) *

Does this help anyone identify the stroke?

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

Since you have the crank available, you just need a ruler.
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Todd Enlund
post Apr 25 2009, 03:53 PM
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QUOTE(McMark @ Apr 25 2009, 02:06 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.

Yeah, that's why I mentioned "cylinders" and "stroke alone won't give you the answer"... (IMG:style_emoticons/default/tongue.gif) I guess between all of us we covered the bases...

QUOTE(knuckledrgr914 @ Apr 25 2009, 02:22 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

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.
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knuckledrgr914
post Apr 25 2009, 03:53 PM
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QUOTE(ArtechnikA @ Apr 25 2009, 03:41 PM) *

QUOTE(knuckledrgr914 @ Apr 25 2009, 05:22 PM) *

Does this help anyone identify the stroke?

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

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

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 (IMG:style_emoticons/default/screwy.gif) Based on the attached picture, could you dumb it way down for me? (IMG:style_emoticons/default/pray.gif)

Thanks,
Brad

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ArtechnikA
post Apr 25 2009, 04:00 PM
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QUOTE(knuckledrgr914 @ Apr 25 2009, 05:53 PM) *

could you dumb it way down for me?

red line - crankshaft centerline
green line crank throw line


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knuckledrgr914
post Apr 25 2009, 04:03 PM
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QUOTE(Todd Enlund @ Apr 25 2009, 03:53 PM) *

Those rods are for the 66m 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.


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
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knuckledrgr914
post Apr 25 2009, 04:12 PM
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QUOTE(ArtechnikA @ Apr 25 2009, 04:00 PM) *

QUOTE(knuckledrgr914 @ Apr 25 2009, 05:53 PM) *

could you dumb it way down for me?

red line - crankshaft centerline
green line crank throw line

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

Bra
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knuckledrgr914
post Apr 25 2009, 04:27 PM
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QUOTE(ArtechnikA @ Apr 25 2009, 04:00 PM) *

red line - crankshaft centerline
green line crank throw line

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

Thanks,
Brad

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McMark
post Apr 25 2009, 07:29 PM
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Those rods are for a 66 stroke crank. If those rods came off that crank, it's a 66.
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jd74914
post Apr 25 2009, 08:17 PM
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QUOTE(knuckledrgr914 @ Apr 25 2009, 04:22 PM) *


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Bad day removing rings? (IMG:style_emoticons/default/biggrin.gif) Sorry, I couldn't resist (IMG:style_emoticons/default/happy11.gif)
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knuckledrgr914
post Apr 26 2009, 08:45 AM
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QUOTE(McMark @ Apr 25 2009, 06:29 PM) *

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


Thanks McMark!

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


Go ahead jd74914... Laugh at other's misfortunes why don't you!!! (IMG:style_emoticons/default/lol-2.gif)

Ya, I guess I could have cleaned up my backdrop a tad. Thanks for pointing it out (IMG:style_emoticons/default/mad.gif)

Brad
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