Inliners International Forums General Discussion Engines Specs needed for a Chevy I6 (cast # GM 3877178)

Hi all, I'm new to the forum and I just got a 60's something Chevy 10 Stepvan (P10 I think). I've identified the engine blcok as a GM 3877178 which is I guess a 235 or 250 cid. according to the casting number list on this website. I'm having trouble identifying the year of the engine and consequently what kind of carb I need for it and the correct compression numbers for the cylinders. Can anyone point me in the right direction?

Does it have an HEI ignition? Integral style head? No chance of a tag with the carb number on it? The serial number from the P10 will tell you what year the truck is and what size motor came in it but no guaranty the motor hasn't been changed.

I'll check to see if it's an HEI today. It doesn't have an integral head. I can't find the serial number for the van; I found the VIN (P1356Fxxxxxx) but any VIN decoder that I can find for chevy trucks that year don't work as the number I found is one digit too long. There is black painted over label on the wall toward the ceiling labeled "T92766" but other than that I can't find any other number except more codes casted onto the engine. Where can I look for some sort of date code? Thanks again!

230 or 250, not 235...

Did you get a title with the van?

To tell if it is a 230 or 250, check the stamped number on the machined surface just to the rear of the distributor. The code letters will tell what it is when you look it up in a Hollander interchange manual, or contact a Chevy dealership parts counter.

I heard Twisted6 tell someone a while back to look in the spark plug hole and see the shape of the dish on the piston. A D-shaped dish was a 230 and a round dish was a 250.I think that was the correct description he said....

Just the other way around.


MBHD

The 230 is a flat top piston. the 250 is a D shaped dish.

So we looked into the spark plug hole and it looks like a flat top. Guess that means it's a 230. What's the appropriate compression for that? We did a compression test and it hangs around 25 . We added some oil to one of the cylinders and the pressure jumped to about 30, so perhaps a seal issue?

We found the following numbers on the side of the block:

OON2 F16 3877178 C GM27

Any ideas?

You can also guestimate the stroke by putting a coat hanger a stiff ty wrap AKA zip tie,etc, in the spark plug hole when the piston is @ TDC & turn the crank slowly until you are @ BDC.

Measure the distance how far the coat hanger goes down from TDC to BDC.

Top of stroke to bottom of stroke.

MBHD

You only had 25-30 pounds? for compression??? If that is the case
That is not a very good sign for any motor. That sounds like bad
rings or the valves are not closing,Or a bad head gasket. a good motor will push a 120lbs give or take.

x2,
looks like you need to pull the engine apart.

Or @ least do a leakdown check to see what & where it is leaking.


MBHD

F16 could be June 1, 1966.

Again, there should be a STAMPED not cast number next to the dizzy...

Well, I'll take a look again. The engine is pretty grimy, so I'll find it after I degrease it. It should be located right behind the distributor?

Yes, just the rear of it is a machined pad. It will be stamped on that.

Not that I want to add to the bad news, but you could also have a cracked piston. Something is definitely not right inside your motor if you only have that much compression. And like Larry said, it could also be bad rings, burned or bent valve(s), or a blown head gasket. Or a combination of those problems. Is your compression running 25-30 pounds in ALL the cylinders?

I'm not sure how to say this, other than to say it, but are you using the gauge correctly? are you turning it over enough times to get a full reading?

Hi, I found the serial #, F0403FY. Can someone decode this for me?

It's possible we could not be cranking it correctly. This is my first hands on restoration; I got the van in exchange for a laptop and we plan on using it as a gear van for some music gigs. I have a few people with automotive experience but could use any protips this community can throw at me. I really want to avoid taking the engine apart as I'm on a small budget. I'll retest the cylinders tomorrow evening.

Edit: I have my father (jet engine mechanic as of late, used to be car mechanic), a friend in an automotive class, another friend who took a bunch of auto classes, and an acquaintance who restores classic cars.

Also you should be turning the motor over with the STARTER NOT!!
by hand.AND have all the plugs out so that the motor will spin freely.

Yeah we tried with the starter. I think the starter might be bad since it barely turns the engine over. I can hand crank it easy enough but the starter seems to have a bit of trouble. We took it out and tested it; the solenoid appears to fire fine but I couldn't tell if the starter motor was having trouble spinning, sounded and felt off-balance just a little.

I'm getting a new starter and a 1000cca battery and charger. Hoping to get to the bottom of this compression issue. Is there any other procedure I can do to narrow down possible causes?

Repost
do a leakdown check to see what & where it is leaking.

That is a tool w/two gauges. Bring piston to top dead center
(compression stroke) apply compressed air in through the spark plug hole,etc,etc,etc
http://www.pegasusautoracing.com/productdetails.asp?RecId=5380

MBHD