Opel GT Forum banner
1 - 7 of 7 Posts

·
'69 GT- Guards Red
Joined
·
26 Posts
Discussion Starter · #1 ·
I'm thinking about stroking a 1.9 L to 2.2 by offset grinding the crank for use with an aftermarket Honda Connecting Rod. I'm looking at the Probe #1203-12039 ($279/4) with a Journal Diameter of 1.770 and a Big End Width of .935. This allow for a stroke increase of .275. The downside (?) is, with no welding, the side clearance will be .043, normally .008.

Has anyone ran this large of clearance? Will the oil pressure be too low?
 

·
Super Moderator
Joined
·
14,143 Posts
I assume you're looking at the B18B rods, correct? You can run this rod, keep in mind you can offset grind the crank and keep whatever width you want. There will be one area (the furthest 'out' section of the crank throw) that will have the added clearance, but you can make the rest of the journal the narrower width you need to keep clearance at a minimum. Others have used narrower rods (namely BMW) and have run WITH the extra clearance. Oil pressure at idle drops, but it's not bad once under way, certainly no big deal for a racing engine.

Oh, and one other thing. You will probably not get the full .275" stroke increase. This would entail the crank having NO wear and the crank grinder finishing the journal exactly where the outer limits of the stock journal are. Not likely. Probably easier to shoot for .260-.265" more stroke. With this much stroke, and a 97 mm bore, you can get 2490 cc's from your 2.2.

Bob
 

·
Member
Joined
·
149 Posts
On a street engine would the extra clearence on the outside of the crank be an issue? Could you offset grind a little less stroke into the crank to give additional side clearence if it were an issue?

Darrin
 

·
'69 GT- Guards Red
Joined
·
26 Posts
Discussion Starter · #5 · (Edited)
RallyBob,

I'm looking at a rod for the B16A with C to C length of 5.43 and a .827 wrist pin. It would be nice to find a std Chevy piston that would work, but the pin diameters are too big (.9272). Is it practical to bush the pin bore of a piston?

I'm looking at Ross Custom. I picked 3.736" + .030 over (95.65mm) for the bore. 97mm Bore?, are the cylinder walls getting too thin?

Something like this (see attached model)? This is with an offset of .125 and a 1.770 journal diameter, for an increase in stroke of .250. I don't see a problem with the extra step.
 

Attachments

·
Super Moderator
Joined
·
14,143 Posts
Nice model! Yes, that was what I was talking about. It won't be an issue for the street, as long as all other oil tolerances are reasonable.

You can take a 2.0/2.2 (same block) or 2.4 block out to 97 mm no problem. That's how I make 2.2's into 2.3's and 2.4's into 2.5's. The 'problem' is with the head gasket. Either get a German racing gasket ($180 or so) or use a copper one. I went with the latter choice, and had some 'big-bore' copper head gaskets made for the Opel engines. If you want, you can punch the block out to 96 mm and use the stock 2.0 gasket still. I also recommend using 1.5/1.5/3.0 mm rings, as they have less surface friction and seal better than the wide Opel rings. You'll also find that rings are readily available in 96 and 97 mm bores, even the Total Seals.

BTW, I think (been a while) I chose the B18B rod because it was wider than the B18A and B18C.

Bob
 
1 - 7 of 7 Posts
Top