At 10:19 AM 3/20/95 -0600, Todd Mullins wrote:
>I've been reviewing Scott Fisher's recent narrative (of 6 Jan)
>describing his MGB lump, and I think I'd like to do something similar.
>Scott uses a '73 18V block with early, angled-big-end rods and early
>8.8:1 compression pistons. Two questions come to my mind:
>
>1. Is there actually any benefit to the angled big-ends?
Only if you want to run consistently over 8000 RPM, in which
case you also need to do things to the crank's oilways. It's a
durability issue primarily for race motors.
I have been making up other plausible reasons why my race
engine consultant suggested the 18G type rods. Another good
one is that there is about twice the area of thread contact on
the early rods, in which the bolts screw directly into the rod.
The 18V rods are held on with bolts that drop through the con
rod from the top and have 12-point nuts torqued down to the
ends. The 18Gwhatever rods have bolts that go through the
cap and screw into the main body of the rod itself, and there's
about twice, maybe three times as much threaded area on the
rod bolts going into the rod as there is when you put the nuts
onto the rod bolts on the 18V. That would mean less stress
on a given area of steel on rod or bolt when the engine is in
operation.
Again, I should stress that I'm making up that reason. It could
be plausible, and it could be ludicrous. You get to decide which
one works best for you...
>2. If I should choose to retain my 18V (straight big-end) rods, will a
> swap to the earlier pistons provide me with the 8.8:1 compression
> ratio? In other words, are the effective lengths of the 18G and 18V
> rods the same?
I think the center distances of the rods are the same across all 5-main
engines (where center distance = big end to little end, measured at
the centers of the holes).
> Are there any problems with swapping the gudgeon
> pins?
Yes. There are three ways you fit the gudgeon pins into the little end
of the connecting rod: by a pinch-bolt on the con rod (which I think
only happens on three-main rods); by a full-floating pin held in by
circlips (which is the 18G rod and piston like I've got); and by a press-
to-fit gudgeon (which is what your 18V has).
There may also be problems with the pin to piston fit, but I have no
way of knowing; it's just something you should check.
>In other news, the garage (with the house attached) is coming along
>nicely...
Oh, right. We get to find a new garage; the people who own the
house ours is attached to have to sell suddenly. At least I've found
a bigger garage that's got an office on the other side of a little atrium,
so I've got a place for my cars and my computers; there are a couple
of bedrooms and some very nice mahogany paneling in other
parts of the structure that connects the garage to the office. One
weird thing: the garage has sliding doors, which are kinda cool
but mean you can't have both doors open at the same time.
--
Scott Fisher
fisher@avistar.com SEFisher@AOL.com
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