Hello!
Next week I will send my case to machinist to drill sets for new cylinders 90.5! I need some advice what to watch! What can be wrong? I have A41 case with 10 mm studs. I know that now place for cylinder bottom is tinnier (on case)! How deep to go with hole in case? How deep on surface of case? Thanks for any advice! Same question for my heads 040!
Regards!
Tomica!
Advice for my machinist ?
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Marc
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Gene Berg:
"All cylinders that have 96mm or larger spigot holes, require that the case seating area be surfaced about 0.060" to provide a full seating area for the cylinder to set on, the same thickness all the way around the cylinder base. Subject to this is thick wall 90.5, 92, and 94 cylinders. This must be done in a milling machine, jig bore, Rotler case center, etc. It cannot be done with our GB 700 tool. If not done, it is possible to start having leaks at the base, especially later in the life of the case."
You'll notice that there's a slight step (~6mm long) on the spigot of the 90.5 cylinders. The case needn't be bored to that diameter for the full depth, and the more metal you leave the stronger it'll be. Ask him how much more it'll cost to "step-bore" the holes - it'll be OK if he doesn't, but it's a nice touch, as is radiusing the bottom of the cut. Take him a stock barrel and a 90.5 so he can duplicate the clearances
"All cylinders that have 96mm or larger spigot holes, require that the case seating area be surfaced about 0.060" to provide a full seating area for the cylinder to set on, the same thickness all the way around the cylinder base. Subject to this is thick wall 90.5, 92, and 94 cylinders. This must be done in a milling machine, jig bore, Rotler case center, etc. It cannot be done with our GB 700 tool. If not done, it is possible to start having leaks at the base, especially later in the life of the case."
You'll notice that there's a slight step (~6mm long) on the spigot of the 90.5 cylinders. The case needn't be bored to that diameter for the full depth, and the more metal you leave the stronger it'll be. Ask him how much more it'll cost to "step-bore" the holes - it'll be OK if he doesn't, but it's a nice touch, as is radiusing the bottom of the cut. Take him a stock barrel and a 90.5 so he can duplicate the clearances
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Guest
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Marc
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Basically. Since decking the case to provide a flat seating surface will probably take away most of your deck height, expect that you'll need cylinder spacers or head gaskets to get safe piston-to-head clearance; if you use cylinder spacers, the cylinder won't be plugged into the case quite as deeply so there'll never be a need for any "extra" depth - he only needs to go deep enough to allow the barrel to just fit.
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kangaboy
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AcyTom2
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Hi!
Thanks for your help! I'm living in Croatia and here I don't have any VW machinist, just regular machinist. In my experience some of them a good and some of them just work to work, without care just to make money. So I need to know more about what I wont to help him! Thanks again!
Regards!
tomica
Thanks for your help! I'm living in Croatia and here I don't have any VW machinist, just regular machinist. In my experience some of them a good and some of them just work to work, without care just to make money. So I need to know more about what I wont to help him! Thanks again!
Regards!
tomica
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maxyboyvw
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- Joined: Wed Sep 11, 2002 12:01 am
tomica,
just ask the questions. dont worry if you think they're stupid or not or whatever other people may say. its better to be sure. assumptions cause problems in the future. ask, read, research, ask, ask again, read, measure, measure, measure, and cut once.
so does anyone have any idea why the way to bore 94s and 90.5 cylinder bores are different? step-bore vs straight bore.
do you have to remove material where the cylinder mates with the case cylinder bore (the reinforced part) so that it is flat/sealing on the cylinder?
pics of the step bore would help tomica and me. i'll be sending my case to be cut soon.
thanks.
just ask the questions. dont worry if you think they're stupid or not or whatever other people may say. its better to be sure. assumptions cause problems in the future. ask, read, research, ask, ask again, read, measure, measure, measure, and cut once.
so does anyone have any idea why the way to bore 94s and 90.5 cylinder bores are different? step-bore vs straight bore.
do you have to remove material where the cylinder mates with the case cylinder bore (the reinforced part) so that it is flat/sealing on the cylinder?
pics of the step bore would help tomica and me. i'll be sending my case to be cut soon.
thanks.
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Marc
- Moderator
- Posts: 23741
- Joined: Thu May 23, 2002 12:01 am
Well, if there's no step on the cylinder spigot it'd be rather pointless to step-bore the case....maxyboyvw wrote:...so does anyone have any idea why the way to bore 94s and 90.5 cylinder bores are different? step-bore vs straight bore.
do you have to remove material where the cylinder mates with the case cylinder bore (the reinforced part) so that it is flat/sealing on the cylinder? ....
As it says in the Berg quote above, you must deck the case for 94s and 92/late90.5s in order to get a full-width flat seating surface for the cylinder. Some cases have enough material in the casting around the cylinder bore to allow you to get away without this for the 92/late90.5 size, but most don't.