Dustin,
I recommend you acquire a 6-bolt 270 crank and flywheel. GMC changed to
this design for a very good reason - 4 bolts don't do a very good job of
holding the flywheel on, even on a stock engine.
Considering your intended application with the turbo, you can expect
increased torsional flexing of the crankshaft. This WILL cause flywheel
bolts and damper pulley to loosen. You will need all the additional
fastening capacity of the 6 bolt flywheel; and even 6 bolts may not be
enough. This is the Achilles heel of any inline engine turned past its
recommended RPM range. Even the later 7-main 292 engines suffer this
problem, and it's worse on the older 4-main design.
Also consider that the clutch bolt pattern of your old flywheel may limit
you to a clutch that may not be adequate. If you have the 11" 9-bolt clutch
pattern on your flywheel, there is no modern clutch that will fit. This
clutch will not tolerate anything much over 4,000 RPM on a repeated basis. I
had a pressure plate explode on one of these clutches, and it a very scary
experience.
The 302 that I now have under construction has the crankshaft flywheel
flange turned down to accept a modern V8 flywheel, which provides a huge
variety of modern high performance flywheel and clutch combinations. I
think you would be well advised to look into something like this, but at a
minimum, you will save yourself much grief by upgrading to the later 270
crank.
JAck / Winter Park FL
----- Original Message -----
From: <CLLLSLS@aol.com>
To: <oletrucks@autox.team.net>
Sent: Friday, March 24, 2000 7:37 PM
Subject: [oletrucks] 270 crank saga continues...
> Hey everyone,
>
> Well, I called a few local core shops and one actually had a 4 bolt 270
> crankshaft, but it was same condition as the one I've already got. Lots of
> the later 6 bolt 270 cranks are still around. I came across 3 locally
while
> searching yesterday. I asked each core shop I called if they could think
of
> anyplace else that might have one. They each rattled off a list of several
> crank grinding shops I should talk to. So I called 8 or 9 crank shops and
> none of them had one. BUT, I talked with these crank shops about my crank
> and, I know they're trying to make a buck, but they were actually pretty
> enthusiastic about fixing the crank I have. Someone from this list
suggested
> I look into welding or spraying metal on the crank, but everyone I talked
to
> said they won't do that with automotive cranks. Don't know why. They
actually
> said that pits from corrosion on the journals won't effect anything as
long
> as they are smooth. The crank's biggest problem is the corrosion on the
rear
> seal surface. This can't be turned down because then it wouldn't seal,
but,
> someone on this list actually suggested chroming the surface and grinding
> back down to original dimension. A couple of the crank shops actually
> confirmed they'd heard of doing this, they don't do it, but they've heard
of
> it.
>
> As it turns out, I talked with my dad about this and he just sent out a
> coupla worn machinery shafts to be built up with hard chrome where he
works.
> I might be able to use his companies account to get the chroming done.
>
>
> I also want my crank nitrided. My machine shop tells me it's overkill, but
I
> have some experience trying to locate a 270 crank and it's not fun. I'd
> rather pay the extra $50 for nitriding now with the hopes of increasing
the
> odds of my crank coming out alive if my turbo 270 grenades a rod or
something.
>
> Sooooo... I'm gonna bring my crank down to one of these crank shops and
have
> them look at it. If it's good I'll be grinding, chroming and nitriding.
>
> Thanks for all the responses to my crank search. I guess I might not need
> another one after all.
>
> Dustin
> 50 & 53 GMC 1/2 tons
> 48 GMC 3/4 ton
>
>
> oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
>
oletrucks is devoted to Chevy and GM trucks built between 1941 and 1959
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