Engine rebuild question

[Benyon]

Currently following the Tom Wilson book (Rebuilding your air cooled VW engine) and I have a couple of questions...

I have an AS21 1600 case.

There is a point in the book where it corrects itself regarding the orientation of the lovered bit of tin that sits below the alternator/dynamo stand. The piece I took off had the louvres opening up with the flat side towards the fly wheel, the pictures in the book show the louvres opening down with the flat side towards the flywheel, but the writing suggests louvres down flat side towards the outboard side of the engine. Can anyone tell me which is correct, and why?

Also, regarding pistons, the book suggests buses had dished pistons to lower the compression and reduce the chance of detonation in a hotter running bus engine and that deck height should be 1mm to 2mm. When I took my engine apart each cylindar had a 1.5mm shim on and when I put the pistons and cylindars back on with the shims the deck height was around 3mm. Would these shims be to compensate for having flat headed pistons ie. to reduce the compression?

Sorry didn't take any pictures!?

Andy

 

[noddy]

Louvers down and oposite to the rotation of the crank, if you get this gasket in incorrectly it catches flung oil from the crank.

As for the shims, most engines have shims to correct the deck height, and I think thicker shims are used in recon bus engines, dished pistons are no longer available.

 

[Benyon]

Ok louvres down, so opposite to rotation of cracnk would be flat side towards cylinders 1 & 2?

What should my deck height be, am I correct in thinking between 1mm & 2mm? Also what compression should I be getting, or aiming for?

Cheers ears :mrgreen:

 

[noddy]

If I remember rightly louver openings point outboard.

As for compression sorry dont think I can be much help there, does the book give a compression ratio? it should be possible to work this out from the bottom of the stroke being 1:1 to the top of the stroke beings the compressed amount.
Not sure if I am right in this but sure Ive seen a kit that uses disks and fluid to work out compression, maybe someone who is more o fay with engines can answer this.

 

[fredster]

Measure deck height, measure cc's of head chambers then go here to calculate compression ratio: http://www.aircooled.net/gnrlsite/resource/specgeninfo/calcs.htm" onclick="window.open(this.href);return false;

As a (VERY) general rule stock tp head chambers are 50cc.

 

[Benyon]

Thanks guys for your help.

Alternator pedestal is back on, still waiting for the cylinder heads to come back from machining - they are being bl**dy slow!!!

From the above I will be running a compression ration of 6.8:1 approx, does this sound a bit low?

 

[ronmidg]

my haynes bay manual lists the compression ratio for the 1600 at 7.5 from april 68 on which would cover the AS engines (down from 7.7 for pre april 680. there are references to 7.3 as well in intereurope and autobooks but I suspect this is for rubbish petrol.