I talked to a guy at the dyno day and he said his was .020 over bore. I was shocked he was that loose, but he said thats what the shop did. You would think it would not work well. Its way worn out when new.

 

Eh, it isn't so important when you get to triple digit boost............

 

UPDATE::::

Started thinking a little different about the overbore and going with just .005" instead of a loose .018". After sitting on my porch stairing at the old truck, I know I'll likely drive it more than just down the track, I love these old trucks. So, going with a tighter spec. I just hope it doesnt take forever to break in and make diecent power.

 

From the FSM
1. Max cylinder bore 102.116 mm (4.0203")
2.Max Out of round .038 mm (.0015")
3.Max taper .076 mm (.003")
4. Min piston diameter 101.880 mm (4.011")
5. Max bore minus minimum piston diameter 102.116 mm - 101.880=.236 mm max
clearance (4.0203"-4.011"=.012" max clearance)
6. when subtracting the max wear limit of the piston 101.823 mm from the max bore 102.116 mm you get and absolute max (1 more straw and the camel is toast) = .293 mm absolute max limit, you would not want to build a new engine to this spec...Mark

 

This applies also:

Nominal data:
1. bore-102 mm (4.02")
2. piston wear limit 101.823mm (4.0088")
3, ring gap top-.040-.070 mm (.0160"-.0275"
middle-.25mm-.55mm (.010"-.215")
bottom-same as middle

 

Before it is pointed out to me, these are standard specs, any over size is then added to the standard spec resulting in the same tolerances...i.e. 4.0203"+.010" ("10" overbore)=4.0303" the new bore size...Mark

 

Thanks Mark, that all great info! I was looking for some good ring gap measurements.

 

No problem, remember that the ring gap will remain the same, regardless of the over-bore. the rings will be sized relative to the pistons...Mark

 

Let me know if you need any other specs, got the ole' book right next to the computer...Mark

 

Note the edit in gap info, I had brain flatulence...Mark

 

I would probably give Schieds a call and ask them .

I have my own opinion and it differs from everyone elses, but I have no experience building Diesel motors. I will be going through the same thing here in a few months.....so I am reading all this.

 

The block is done and just waiting on freeze plugs that should be in today. So the build will likely start tomorrow night! I have way too much to do before sunday. Not sure I'll make it.

 

I hate to nit pick, but......

Ring gap is a function of bore size. So, it grows with over-bore. It doesn't even really matter what engine they are going in. It is determined by: the bore size, ring style and intended application.

 

That is why they make over-size rings for over-size pistons...Mark