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Simewill
Samba Member
Joined: March 23, 2017
Posts: 2
Location: Melbourne
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 Posted: Thu Mar 23, 2017 3:49 am Post subject: Case Machining Help - 94mm for 1915cc |
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Hi all,
I am a noob here building a 1915 for a 64 Karmann.
I am about to get the cases pend up to take the 94mm pistons and barrels and the machinist has asked how much tolerance I require...
Anyone out there done this and can give me an idea of what they should be?
Im using a SCAT econo engine kit so any tips from your experience with these kits is appreciated too.
Thanks in advance! |
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kokanee
Samba Member
Joined: April 15, 2007
Posts: 329
Location: Washougal WA
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| Posted: Thu Mar 23, 2017 8:39 am Post subject: Re: Case Machining Help - 94mm for 1915cc |
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| Sounds to me like he has never done a vw case before I think I would find a different shop |
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raul arrese
Samba Member
Joined: July 23, 2006
Posts: 1330
Location: miami florida
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| Posted: Thu Mar 23, 2017 8:54 am Post subject: Re: Case Machining Help - 94mm for 1915cc |
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Cant go wrong with 0.005 to 0.010 but it depends on what tool they use .. one of those drill press bore jobs will be loose usually and still work fine .. I would like looser than tighter ..
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modok
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Joined: October 30, 2009
Posts: 26790
Location: Colorado Springs
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| Posted: Thu Mar 23, 2017 5:28 pm Post subject: Re: Case Machining Help - 94mm for 1915cc |
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yeah, .005-.010 clearance is good.
Have to remove about 1.5mm from the surface.
Stock cylinder surface to crank center is about 100mm, you want 98.5 |
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Simewill
Samba Member
Joined: March 23, 2017
Posts: 2
Location: Melbourne
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| Posted: Thu Mar 23, 2017 7:08 pm Post subject: Re: Case Machining Help - 94mm for 1915cc |
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Thanks for the responses. The shop normally does v8 stuff but I am limited for choice around here. Thanks for the responses  Looking forward to getting the car on the road! |
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stealth67vw
Samba Member
Joined: January 22, 2004
Posts: 1852
Location: Grass Pants, Orygun
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| Posted: Thu Mar 23, 2017 9:02 pm Post subject: Re: Case Machining Help - 94mm for 1915cc |
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The case will also need to be decked .060" to get a complete sealing surface.
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John Bates
JB Machining Services
1967 street Bug 2276 w/ 48 IDAs, 2020lbs with driver
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Rome
Samba Member
Joined: June 02, 2004
Posts: 9654
Location: Pearl River, NY
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| Posted: Fri Mar 24, 2017 5:36 am Post subject: Re: Case Machining Help - 94mm for 1915cc |
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That would be the 1.5mm which Modok listed.
The machinist should cut a new ledge to the depth indicated, which moves the entire cylinder inwards toward the center of the engine. This reduces your deck height, due to the 94mm cylinders being 1.5mm longer than other, smaller-sized cylinders. |
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raul arrese
Samba Member
Joined: July 23, 2006
Posts: 1330
Location: miami florida
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| Posted: Fri Mar 24, 2017 6:03 am Post subject: Re: Case Machining Help - 94mm for 1915cc |
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| Rome wrote: |
That would be the 1.5mm which Modok listed.
The machinist should cut a new ledge to the depth indicated, which moves the entire cylinder inwards toward the center of the engine. This reduces your deck height, due to the 94mm cylinders being 1.5mm longer than other, smaller-sized cylinders. |
Modok said "about" .060 , what you want to do is clean up the area where the jug sit's so you have a nice flat sealing area , I like to machine off just enough to set my deck height to about .040
_________________
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" Bug Jam best motor and best paint "
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nsracing
Samba Member
Joined: November 16, 2003
Posts: 9481
Location: NOVA
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| Posted: Mon Mar 27, 2017 9:15 am Post subject: Re: Case Machining Help - 94mm for 1915cc |
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THAT IS THE PROPER QUESTION - from a proper machinist. You have to know your tolerances. He knows what is doing.
If you just bore a hole in there -that is an idiot. I don't want anyone machining anything for me.
0.005" - .0075" clearance is good for cylinders and heads. I find 0.010" a bit too loose for my taste. The industry standard is way more than that. 
Tell the machinist you want several rough passes and then a final finish cut to proper bore size. That is how I do mine.
We had a video here once a hack cut a case open w/ one pass. And it was new case too. Broke my heart to see that one. Unless it is a giant reamer, we NEVER do just one pass. |
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nsracing
Samba Member
Joined: November 16, 2003
Posts: 9481
Location: NOVA
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| Posted: Mon Mar 27, 2017 9:18 am Post subject: Re: Case Machining Help - 94mm for 1915cc |
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Also, ask the machinist to cut a chamfer on the corner to give you a small bevel so the cylinder bottom will sit in the bore properly.
A cleanup pass on the seating surface will be nice too. But if you do cleanup, make sure you take the same amount on each side.
Good luck. |
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