Case Dimension?

[Trackrash]

Can anyone tell me what the dimension is when measuring from the parting line of the case to the cylinder mounting surface?

We have just split the case on a motor that according to the documentation was "linebored to standard". FWIW, the bearings are stamped std. The other thing is that the deck height we measured with no base gasket and new JE pistons is ZERO.

I want to confirm if the case halves were machined before being "linebored". I have not yet measured the case bores.
Thanks.

[Zuffenwerker]

The last case I measured was 112.1mm - itwas an SC case.

BTW The case could have had the standard size cutter sent through the main bores without machining the case halves.


Daniel

[Trackrash]

Thanks. Once we get stuff cleaned up in a couple of days I'll do some measuring and figure out what is going on. Probably correct that they just cleaned up the case bore, not really doing a true linebore. I'll report back once we get everything accurately measured. The cylinders haven't been shortened and there were standard .25mm base gaskets in there, so we need to see what is causing the 0 deck clearance with the new JE pistons. Looks like 1mm base gaskets may be in our future, but I would like to avoid that if possible.

[Zuffenwerker]

Wow ya sounds like you’ll need a pretty good size shim. I did an engine recently that ended up with a 1.5 or 1.75 shim pack and it was ok no leaks. The heads had been cut a lot and the pistons provided were 11.5:1 so it took quite a bit to get the comp down.

Daniel

[Trackrash]

I just heard from the owner that he measured around 111.5mm with a caliper. So it does indeed appear that the case did see some milling. Further investigation is required. The main thing is to check for the line bore to be in spec. Fingers crossed.

At least this problem is easily fixed with shims. LOL

Weirdly the motor had standard .25mm cylinder shims from the last build. We are still waiting on the heads to see what thickness of shim we will need this time.

[mikedsilva]

Originally Posted by Trackrash

I just heard from the owner that he measured around 111.5mm with a caliper. So it does indeed appear that the case did see some milling. Further investigation is required. The main thing is to check for the line bore to be in spec. Fingers crossed.

At least this problem is easily fixed with shims. LOL

Weirdly the motor had standard .1mm cylinder shims from the last build. We are still waiting on the heads to see what thickness of shim we will need this time.

I thought std shim thickness was 0.25mm?

[Trackrash]

Originally Posted by mikedsilva

I thought std shim thickness was 0.25mm?

Correct. I'll edit my post.

[Henry Schmidt]

Here's another consideration:
If the case halves were machined to allow for a return to standard main bearing bore (pretty common practice these days), the amount of machining seems critical.
Every .001" reduces the backlash on the distributor gear. To my knowledge that clearance can not be easily recovered.
Hummmm?

[Trackrash]

Originally Posted by Henry Schmidt

Here's another consideration:
If the case halves were machined to allow for a return to standard main bearing bore (pretty common practice these days), the amount of machining seems critical.
Every .001" reduces the backlash on the distributor gear. To my knowledge that clearance can not be easily recovered.
Hummmm?

I hadn't heard that, good to know, although we will be using a crankfire ignition.

This motor was rebuilt and "linebored" many years ago, so who knows if the parting line was machined. I can install a distributor and see if there is any binding of the drive gear.

How is it possible to determine where material was previously removed? From the cylinder seating surface or the parting line?

[Neven911]

Lineboring to standard would remove 0.25mm? From the case faces in addition the spigot faces may have been cleaned up which would remove more height, the mag case on my 2.4 was quite hammered

[Trackrash]

Turns out the case crank bore is standard. Apparently the seating surfaces were machined, it appears, I'm guessing 0.010". Also the cylinders measure in 0.004" under spec in height.

Here is the other thing, the 92mm JE pistons have a 0.015" HIGHER "compression distance" than the Mahles that were original to the motor. Meaning the deck height of the JE pistons is 0.015" higher than the Mahles. BTW the comp. distance of the JE pistons measures in spec with their data sheet.


The weirdest thing is the motor had only the standard cylinder base gaskets meaning the the old pistons had very little deck clearance. There is some indication of this as there is no carbon on the edges of some of the pistons.
The other thing is the case is going to need to be fixed, so when we get it back we will need to do some more measurements.