Volkszone Forum banner
1 - 13 of 13 Posts

·
Registered
Joined
·
310 Posts
Discussion Starter · #1 ·
Can anyone give me detailed information on what you have to do to the case and heads of a type 1 engine to fit larger cylinders? Got a mate who can do the work but he wants to be sure he has info for these engines.
 

·
Registered
Joined
·
912 Posts
1st you need to inspect the case to see if it's worth this modification. Check bearing saddles, check for cracks, does it have corrosion, does it have centre main bearing spread etc
 

·
Registered
Joined
·
310 Posts
Discussion Starter · #3 ·
1st you need to inspect the case to see if it's worth this modification. Check bearing saddles, check for cracks, does it have corrosion, does it have centre main bearing spread etc
Yes, but what is the process of modifying the case and heads?
 

·
Registered
Joined
·
912 Posts
You want a vw machine shop with the proper flycutting tools really.
 

·
Registered
Joined
·
310 Posts
Discussion Starter · #5 ·
You want a vw machine shop with the proper flycutting tools really.
Well my mate who is doing the work has a fully set up machine shop, with two Mills at the moment. He works with beetle engines building trikes. Restores classic alfa romeos professionally from making the body panels by hand upwards. So I am confident he can do the work.
He just wanted me to check what exactly needs to be done for myself so I know if he is doing it right .
 

·
Registered
Joined
·
5,946 Posts
If he's got to ask you then find someone else who knows what they're doing. Isn't he the one that should be finding out what to do?
 
  • Like
Reactions: rakatak

·
Registered
Joined
·
310 Posts
Discussion Starter · #7 ·
If he's got to ask you then find someone else who knows what they're doing. Isn't he the one that should be finding out what to do?
I trust him to do the work right. He knows what to do.
He's asked me to find out exactly what needs to be done so that I know he has done the work correctly.
Can anyone actually tell me what the detailed procedure is?
 

·
Registered
Joined
·
912 Posts
Cutting a case for bigger cylinders is done after you have checked the case is even worth doing. I'm trying the help you here..
 

·
Registered
Joined
·
66 Posts
Not much to it really, but the accuracy has to be very good. You are opening the case bore to enable the larger cylinder to fit. Just measure the new cylinders and go for a “slip fit”. The sealing face is the outer rim of the case against the cylinder shoulder. With the larger 94mm piston, if you have thread-inserts in the case for the head studs, they may need spot faced to stop them interfering with the sealing face. Obviously the bore needs to be concentric and equidistant & perpendicular from the case split. Similar story for the head. You are widening the bore for the cylinder, without messing up the sealing face as there is no head gasket. Changes to the depth of sealing face, is a “fly cut” and increases compression (must be identical for each cylinder or the head will sit crooked & leak).

Common sense really.

But as above, check the case dimensions are within spec or you are wasting your time.
 

·
Highly Respected Member
Joined
·
13,527 Posts
Obviously the bore needs to be concentric and equidistant & perpendicular from the case split.
It actually needs to be concentric and equidistant & perpendicular from the crank centreline, which due to case manufacturing intolerances, may not be the same as the case split line. - Assuming you want the most accurate job and don't want the pistons running crooked.

I remember reading something on the JMR website about this - crank centrelines can be slightly out from the case split, and sometimes out more at one end than the other. You'll need to depth mic all the bearing saddles to work out where the true centreline runs, then take that as your baseline for all your cylinder hole machining operations.

Dave.

Edit - Here's the page in question - John Maher Racing » Internal case modifications
 

·
Registered
Joined
·
310 Posts
Discussion Starter · #13 ·
Thanks for all your replies, I've taking it all on board, done a bit more research, talked to my mate. and now just waiting to take the trike off the road, strip the engine down so he can bore the case and heads for me.
 
1 - 13 of 13 Posts
Top