Motor swap for 68/69 Franken-G

Greetings martians, your help is sought once again!
I've driven my G20, with the extremely rare "unshaven bum" factory package, happily thousands of miles since I bought it 2 years ago.
The reman. 250L6 has gone from adequate compression to low, to downright droopy (70 in #2, 105 in all the others).  Ive known that a replacement was coming so its no big shock, I just wish I was a bit more flush with cash to do it.
So, the two local choices are both used and both out of vehicles so comp. test is not possible.

1: 1977 292, complete less water pump, stored 15 years in heated garage as a backup engine, 70,000 miles, running when pulled. $150

2: 1967 250, complete less dizzy, pulled for a V8 swap 1 year ago, running when pulled, miles unknown.  $400

My question is not about the advisability of installing an untested used engine; I am not rich, and thats how I roll.  Its more about the reality of what will bolt right in and get me back on the road in the shortest amount of time, especially since the 292 is a newer one.  I do build motorcycles and haul a lot, for what thats worth.

I am mechanically sound, own decent tools (but no lift) and have replaced engines before, however always a direct replacement (vw aircooled).
This is questionable shade-tree work that I am embarking on, and I thank you for your time

How about pulling the head, checking the valves and maybe you get back on the road with just a valve job?????
You can do a cylinder leakdown test on all the engines to see how good the cylinders are and find out where, (the rings, exh and intake valves as well as the head gasket) the compression is escaping,,,,,,you just need a source of air like a portable air compressor,,,,,,

the 292 will need an adapter plate for the right motor mount since it is in a different spot than our FAVORITE, 194/230/250 Chevy/GMC 6 cylinder engines also the 292 uses a different size flywheel/flexplate,,,,,,,

Donivan, you're very right about the leakdown test -- I will be doing that in the next couple days, as well as checking if the compression comes up with a little oil in the cylinder. The engine swap idea largely comes from this local 292 for dirt cheap, in seemingly decent shape. I can find an engine mount adapter; can I drill the holes in the flywheel/flexplate out to 1/2" from the existing 7/16"?
Are there other glaring difficulties with this swap?
Can I use the same HEI dizzy from my current 250?
Thanks for the help

If you got a manual trans, you need to check the pilot bushing,,,,,,the carb linkage will be a little bit off since the 292 is taller,,,,,,,and the carb might be a little lean with the bigger engine if you are using the 250 one,,,,,,I think the HEI will fit,,,,,,,,who knows,,,,,maybe that advance curve will work better on a 292,,,,,,,I would check the center hole size also,,,,,,,,but people put those 292's in their vans,,,,,,I would ask a machine or engine shop if they drill out flywheels and if they run into any problems,,,,,,,,

Haven't gotten a chance to do a leakdown test, but will post numbers. I think I will likely pick up this 292 regardless, since its so cheap (pending it being a total mess; I'll do compression test and leakdown with that too)

In the meantime, I have sourced an adaptor for the passenger sider motor mount, and it looks like the HEI distributor I have for the 250 will work for the 292.

For the flywheel, here are two to compare for an 11" clutch

292 -- http://www.rockauto.com/catalog/moreinfo.php?pk=1383363&cc=1031634
250 -- http://www.rockauto.com/catalog/moreinfo.php?pk=1384283&cc=1307786

The only difference I see is in the bolt size (7/16 vs 1/2") and internal balancer vs. not.
Now Im wondering how to figure out what size clutch I have, with a remanufactured 1968 250 in a 1969 G20...
Given a competent machine shop drilling out the holes, can I expect this to work?

Well, these numbers are so bad, I can't really believe its still running --

Leakdown when warm
#1  47% -- past the rings, out the crankcase
#2  86% -- exhaust, has to be a stuck/bent valve i would think
#3  8% -- rings
#4  39% -- rings
#5  23% -- rings
#6  33% -- rings

Compression when warm
#1   115
#2  75
#3  120
#4  115ish
#5  115ish
#6  115ish

Happy Thanksgiving!

OK,,,,,,,the 250's run a 10" clutch........as for the leakage test, 40%  is still in the good range,,,,,70 % is bad,,,,,this is not like compression,,,,its a condition test of rings, head gasket and valves,,,,,,does the engine smoke,,,,how much blow by do you have when you take the oil filler cap off.....does it knock,,,,,,,those are  the real tests of  engine wear,,,,,#2 is surely bad,,,,,,probably a burnt valve,,,,,,the rest at 120 is kind of normal for our tough little 6 cylinder Chevy engines,,,,,,I surely don't give up on the 6 cylinder engines......

I know that the Chevy 6 cylinder engine are tough. I got a 1969 Chevy C10 parts truck in the same woods that my 66 G Van was parked in. It had a 250 6 in it. I had to get a starter for it. Bought a rebuilt 1 bbl carb off of E-Bay for it, and a new HEI distributor plus new plugs and plug wires. I soaked the cylinders with PB Blaster and turned it over to blow out any rust and carbon. I did a compression test on it and #1cylinder had zero compression the rest of the cylinders had between 25 to 45 compression. I soaked it with more blaster and installed the new parts and after a few pops it took off and ran pretty good after it got warmed up. Yes it's warn and needs an overhaul but after sitting in the woods for over thirty years it still runs. Likewise with the little 230-6 in my 66 G-Van. It also sat for around 30 years. It runs better than the 250.

One thing about the valves and valve seats on these old engines. When they were produced, Leaded gas was still in use which the lead lubricated the valves and seats. When gas was switched to unleaded Auto manufactures started using hardened valves and seats in the engines so they would not pre-maturely wear out due to the lack of lead in gas. These old engines need a gas additive or they need their Valves and seats replaced with hardened valves and seats.

Hey all,
Just wanted to update:
Found a good used 250 out of a camaro for $200 with chrome (ooooh!) valve covers and a new head..

 Did a leakdown, everything seemed worth the risk.  Pulled the old one and stuffed in the new, along with a new clutch, all in glorious 20 degree Vermont weather.


Also cut out and replaced the one bit of floor rot with fresh metal welded in + seam sealer.



Played with the timing for a bit before getting it right, runs like a Swatch now.  Loaded him up with two motorcycles and welder, and took off south to Charleston; didn't overheat, ran great with good compression, burns a little oil but so it goes.  

Quite a testament to the old 6cyl design, pretty damn hardy.
In a different vein: does anybody know where I could source a gas pedal assembly for my van?  Having a hard time tracking one down...
Thanks for all the help!