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Braukuche Samba Member
Joined: September 03, 2004 Posts: 10968
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Posted: Mon Jan 05, 2009 5:31 pm Post subject: Stroker engine deck height question |
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I checked my deck height today on my 36 horse Okrassa clone stroker (69 mm) and the piston sticks about 1.94mm above the jug. In order to get factory compression what thickness of ring would I need? Would the copper ring affect this measurement by-the-way?
--Dan |
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mightymouse Samba Member
Joined: May 26, 2004 Posts: 4220 Location: las vegas
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Posted: Tue Jan 06, 2009 6:18 pm Post subject: |
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Id suggest you dont shoot for factory compression. What cam will you be using?
That is the equation. Do the math for dynamic, and static compression, using your choice of cam, and that will tell you where to set your static CR.
Id say deck it at .050"
So youd need a 3.2mm spacer or .127"
Then you can plunge cut the heads a tad to get your compression where you want it.
Last 1600 i did, has a scat C25 cam in it. 9.4 to 1 static compression, and the dynamic compression with that cam is around 7.7 to 1
SO the motor is nice and snappy/responsive, but once its in driving rpm, the compression is perfect for a clean burn, and the heads stay cool.
Youll prob end up setting you static at 8.5 to 1 depending on cam and carbs you use. _________________ Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.
Thomas Jefferson
Note to EVERYONE.
Know your ZDDP levels or you WILL lose a cam and lifters. |
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Braukuche Samba Member
Joined: September 03, 2004 Posts: 10968
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Posted: Tue Jan 06, 2009 7:56 pm Post subject: |
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mightymouse wrote: |
Id suggest you dont shoot for factory compression. What cam will you be using?
That is the equation. Do the math for dynamic, and static compression, using your choice of cam, and that will tell you where to set your static CR.
Id say deck it at .050"
So youd need a 3.2mm spacer or .127"
Then you can plunge cut the heads a tad to get your compression where you want it.
Last 1600 i did, has a scat C25 cam in it. 9.4 to 1 static compression, and the dynamic compression with that cam is around 7.7 to 1
SO the motor is nice and snappy/responsive, but once its in driving rpm, the compression is perfect for a clean burn, and the heads stay cool.
Youll prob end up setting you static at 8.5 to 1 depending on cam and carbs you use. |
Thanks for the info. If I run a 3.2mm spacer, how will that affect my pushrods? What can I do to compensate for the extra distance? I know Okrasa supplied spacers with their kits but did they also include longer pushrods??
--Dan |
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mightymouse Samba Member
Joined: May 26, 2004 Posts: 4220 Location: las vegas
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Posted: Tue Jan 06, 2009 10:17 pm Post subject: |
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Braukuche wrote: |
mightymouse wrote: |
Id suggest you dont shoot for factory compression. What cam will you be using?
That is the equation. Do the math for dynamic, and static compression, using your choice of cam, and that will tell you where to set your static CR.
Id say deck it at .050"
So youd need a 3.2mm spacer or .127"
Then you can plunge cut the heads a tad to get your compression where you want it.
Last 1600 i did, has a scat C25 cam in it. 9.4 to 1 static compression, and the dynamic compression with that cam is around 7.7 to 1
SO the motor is nice and snappy/responsive, but once its in driving rpm, the compression is perfect for a clean burn, and the heads stay cool.
Youll prob end up setting you static at 8.5 to 1 depending on cam and carbs you use. |
Thanks for the info. If I run a 3.2mm spacer, how will that affect my pushrods? What can I do to compensate for the extra distance? I know Okrasa supplied spacers with their kits but did they also include longer pushrods??
--Dan |
Damn, good queston. I need to do some more looking. There has to have been a few people who have had made, or found a way to lengthen the stockers. Since they are 1 piece, i see where you dilemma is.
IF that proves to be too big a challenge, you could always call wiseco, or CP, or any of the other 50 piston manufacturers, and then give them your dimensions and they will make you new pistons. Moving the pin higher would get you juuust right.
You could stay with stock width then, so all your tin will fit correctly.
If you do that, may as well have them make you 3 or 4 sets. Then sell em.
Let us know which route you choose. talk soon. dave _________________ Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.
Thomas Jefferson
Note to EVERYONE.
Know your ZDDP levels or you WILL lose a cam and lifters. |
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Braukuche Samba Member
Joined: September 03, 2004 Posts: 10968
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Posted: Wed Jan 07, 2009 7:01 am Post subject: |
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mightymouse wrote: |
Braukuche wrote: |
mightymouse wrote: |
Id suggest you dont shoot for factory compression. What cam will you be using?
That is the equation. Do the math for dynamic, and static compression, using your choice of cam, and that will tell you where to set your static CR.
Id say deck it at .050"
So youd need a 3.2mm spacer or .127"
Then you can plunge cut the heads a tad to get your compression where you want it.
Last 1600 i did, has a scat C25 cam in it. 9.4 to 1 static compression, and the dynamic compression with that cam is around 7.7 to 1
SO the motor is nice and snappy/responsive, but once its in driving rpm, the compression is perfect for a clean burn, and the heads stay cool.
Youll prob end up setting you static at 8.5 to 1 depending on cam and carbs you use. |
Thanks for the info. If I run a 3.2mm spacer, how will that affect my pushrods? What can I do to compensate for the extra distance? I know Okrasa supplied spacers with their kits but did they also include longer pushrods??
--Dan |
Damn, good queston. I need to do some more looking. There has to have been a few people who have had made, or found a way to lengthen the stockers. Since they are 1 piece, i see where you dilemma is.
IF that proves to be too big a challenge, you could always call wiseco, or CP, or any of the other 50 piston manufacturers, and then give them your dimensions and they will make you new pistons. Moving the pin higher would get you juuust right.
You could stay with stock width then, so all your tin will fit correctly.
If you do that, may as well have them make you 3 or 4 sets. Then sell em.
Let us know which route you choose. talk soon. dave |
Geez, I didn't even think of the tin. You would also end up with a gap there as well. I guess that's why the PO ground the pistons down to make up the difference in the old engine. Maybe that's the route to go, but with a domed piston I wonder if I would get high compression?
--Dan |
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hugheseum Samba Member
Joined: February 11, 2004 Posts: 2690 Location: oregon
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Posted: Wed Jan 07, 2009 8:59 am Post subject: |
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harley davidson pistons _________________ Have a great day! |
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oval56 Samba Member
Joined: July 21, 2003 Posts: 1309 Location: oktoberfest maintown
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Posted: Wed Jan 07, 2009 10:40 am Post subject: |
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for the pushrods, you have to machine some shims on the lathe in 3mm wich you can mount between the pushrod bottom and the tube as distance to length it... like okrasa has written it in the manual
or you machine longer ones (i have to machine it 6mm longer!)
_________________ www.oval56.com
1956 Oval, 2364ccm typ4
1957 Oval Ragtop 1584ccm singel port modified
1950 Hebmüller, 1584ccm okrasa modified
DBK Germany!!!!!!!!!!
www.dbkvw.com |
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Braukuche Samba Member
Joined: September 03, 2004 Posts: 10968
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Posted: Wed Jan 07, 2009 7:35 pm Post subject: |
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I found a little more info searching around and apparently Okrassa inlcuded 3mm spacers for the pushrods. Those should be no problem to make as a I have tons of spare pushrods, but the spacers for the barrel...not so easy. I know WolfsburgWest makes them, but the largest is .060", so I would have to use a combination. Is using multiple barrel spacers a bad idea? If so, any idea where I can find them?
--Dan |
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mightymouse Samba Member
Joined: May 26, 2004 Posts: 4220 Location: las vegas
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Posted: Wed Jan 07, 2009 10:53 pm Post subject: |
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Id bet money, the piston you need already exists. Call a few piston companies, tell em the diameter, the current pin height, and the pin height you need, and they will check their database. prob have the piston in stock. You can prob get em for 60 or so a piston. Make sure they know its an aircooled application, not water cooled.
That would be WAY easier than all this other drama. and same width engine. fits in car better, exhausts fit better, tin fits, sheesh. Like adam said, harley pistons. prob work perf. _________________ Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.
Thomas Jefferson
Note to EVERYONE.
Know your ZDDP levels or you WILL lose a cam and lifters. |
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SGM Samba Member
Joined: December 18, 2007 Posts: 8 Location: Glenn Dale, Maryland
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Posted: Thu Jan 08, 2009 1:40 am Post subject: |
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RIMCO should be able to machine the spacers you need. |
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Braukuche Samba Member
Joined: September 03, 2004 Posts: 10968
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Posted: Thu Jan 08, 2009 7:14 am Post subject: |
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mightymouse wrote: |
Id bet money, the piston you need already exists. Call a few piston companies, tell em the diameter, the current pin height, and the pin height you need, and they will check their database. prob have the piston in stock. You can prob get em for 60 or so a piston. Make sure they know its an aircooled application, not water cooled.
That would be WAY easier than all this other drama. and same width engine. fits in car better, exhausts fit better, tin fits, sheesh. Like adam said, harley pistons. prob work perf. |
At the risk of sounding stupid, if I go this route then won't I negate the extra distance I get with the stroke. In other words, the piston will no longer be traveling the same distance as if I used spacers, right?
--Dan |
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mightymouse Samba Member
Joined: May 26, 2004 Posts: 4220 Location: las vegas
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Posted: Thu Jan 08, 2009 11:51 am Post subject: |
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Braukuche wrote: |
mightymouse wrote: |
Id bet money, the piston you need already exists. Call a few piston companies, tell em the diameter, the current pin height, and the pin height you need, and they will check their database. prob have the piston in stock. You can prob get em for 60 or so a piston. Make sure they know its an aircooled application, not water cooled.
That would be WAY easier than all this other drama. and same width engine. fits in car better, exhausts fit better, tin fits, sheesh. Like adam said, harley pistons. prob work perf. |
At the risk of sounding stupid, if I go this route then won't I negate the extra distance I get with the stroke. In other words, the piston will no longer be traveling the same distance as if I used spacers, right?
--Dan |
You never sound stupid, you simply learn.
No... crankshaft determines stroke.
The piston will travel the same distance up and down no matter what piston or rod you use.
What i suggested will simply move the piston pin closer to the ring lands, thus moving the head of the piston down, and getting your piston top below then end of the barrel.
See the difference between A and B pistos for an example. mahle makes an A for all regular air cooled motors, and B pistons for strokers, to keep the engine at a manageable width.
A 2007cc motor with flycut heads, and B pistons, is more narrow than a 1600, its actually the same width as a 36 hp.
Now you know more. any other Q's ask away. we all love to help. _________________ Nothing can stop the man with the right mental attitude from achieving his goal; nothing on earth can help the man with the wrong mental attitude.
Thomas Jefferson
Note to EVERYONE.
Know your ZDDP levels or you WILL lose a cam and lifters. |
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Back to top |
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Braukuche Samba Member
Joined: September 03, 2004 Posts: 10968
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Posted: Mon Jan 12, 2009 12:35 pm Post subject: |
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Just a follow up for the archives...
I ended up going with spacers to shim out my cylinders to get the appropriate deck height. I bought pistons from two different suppliers: one set from Wolfsburgwest and the other from Matthew who sells 36 engine parts. The set from Matthew had wide skirts and would not clear the crank, They could of course be ground down, but I found the WW set had much narrower skirts and easily cleared the crank, so no grinding needed.
I have the longblock assembled and the engine spins nice. I still need to put the rockers on and deal with the pushrod issue. Thanks to a fellow Sambanista I know that I need to use 3mm spacers for the pushrods. I assume the spacers go between the rod and the lifter. Since these are one piece, I wonder how it is best to separate and then reassemble the rod? I have plenty of extras to experiment on but if anyone has any experience with this I would appreciate any ideas.
--Dan |
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