Stroking/boring M20B25/B27: Sectioned blocks show critical dimensions. PICS!

[nando]

you shouldn't have to cut into that part of the block if you use the 89.6mm crank and S52 rods. AFAIK you only need to clearance things with the 84mm crank because the counterweights are larger in diameter.

[tinkerputzer]

When i test fit my engine (89.6mm crank and s52 rods) using the stock pistons the rod shoulder was just kissing the bottom of the bore. This was while it was still stock 84 mm bore. So i figured once it was bored to 86mm it would be fine. I cleaned up some of the rough casting lines at the bottom of the bore just to be safe though. Clearance at final assembly was some where around .020"-.030"

[digger]

you shouldn't have to cut into that part of the block if you use the 89.6mm crank and S52 rods. AFAIK you only need to clearance things with the 84mm crank because the counterweights are larger in diameter.

some aftermarket rods have larger shoulders than the OEM rods especially H-Beam rods with unnecessarily wide beams , among other reasons ;)

[digger]

i have a junk eta block with the big plug at the back. im gonna cut this bitch up. suggestions and what do people want to look at?

ill measure

-deck height
-cylinder height
-bore wall thickness between and on thrust and no thrust side
-position of oil gallery relative to bore
-position of oil gallery relative to bottom of crankcase

[tinkerputzer]

I'm interested in the oil gallery to bottom of bore dimension. That is where the supposed internal clearance benifits of the eta block are.

[digger]

I'm interested in the oil gallery to bottom of bore dimension. That is where the supposed internal clearance benifits of the eta block are.

is my biggest question to will do.

[digger]

B27 Exhaust Side External View


B25 Exhaust Side External View


B27 Intake Side External View


B25 Intake Side External View

[digger]

B27 oil gallery plug i pressume also big welsh plug on eta


B25 oil gallery plug i pressume


nothing drastically different.

[digger]

The deck height on these blocks are as follows

B25 206.2mm
B27 206.0mm

cant comment of whether material has been removed

the depth of the bore on both is the same at 134.5mm

[digger]

A 90* piece cut from the B27 block. cyl 1 exhaust side. 5.5mm is the thinnest area half way up.



view showing wall thickness at front of bore near where water pump sits. this are is thinnest 4.8mm half way up. is probably the least important areas except for turbo guys



the intake side quarter cut off sits ontop of the block. alot of meat here 6.3mm



a completed cut through cylinder 1



so the oil gallery is much the same position.

[LJ851]

Nice work digger.

[tinkerputzer]

Way to go mate. This puts some things to rest.

[spoolinspoon]

So the b25 would be better suited for boost?

Sent from my Nexus 5 using Tapatalk

[digger]

there are some internal difference which might have a minor effect on fitting the big counterweight 84mm stroke crank. nothing some grinding wouldn't fix

[digger]

So the b25 would be better suited for boost?

Sent from my Nexus 5 using Tapatalk

i would think its much of a muchness.