Projects Old school cool 248 Gmc

Nice work.

 

Well a bit of a slow Saturday. Tried some Alodine on some carb parts, kinda meh. Probably need to clean them better after dipping and need to warm it more. Bought it to do my Stromberg 1BBLs may need to re group. Started resizing the rods and found a bent cap so I pulled another rod out of my spare 248. I weighed the 248 piston to see how heavy the stock pistons were. My buddy surfaced and started adding 4 more 7/16s bolts to the flywheel and crank.

Sent from my S48c using The H.A.M.B. mobile app

 

sorry some of the pics aren't great

Sent from my S48c using The H.A.M.B. mobile app

 

I know you don't need this. But, just for me. Please make sure you get the rear main bearings in the right way around. Many good GMC engines have been lost to careless instillation. None of mine needless to say.

 

Do you have a picture so I won't? I have heard you say this before (I have read most of your posts on gmcs), now I am nervous.

Sent from my S48c using The H.A.M.B. mobile app

 

Just line up the oil holes ...

 

All the main bearings 1 -3 are drilled for oil to reach the crank and rods. Doesn't make any difference which one goes in the block and which one in the cap. As a cruel joke bearing makers only drill one of the rear main inserts. So if you have been lulled into a false sense of security working your way back and don't pay attention you can put the undrilled insert in the block. Cutting off oil to the rear main and #6 rod bearing. Don't do this. It will leave you feeling very sad.

 

ok, I will pay special attention.

Sent from my S48c using The H.A.M.B. mobile app

 

Cleaned, reassembled, torqued, then resized the rods this morning. Buddy just set up the machine and put me to it. I figured it out reasonably quick.

Also started cutting down the 292 damper to fit the GMC. My buddy drill the crank snout and the 4 additional bolts on the crank/flywheel. After we finish the damper we can balance the crank/flywheel/damper assembly. Then to start balancing the rods

Sent from my S48c using The H.A.M.B. mobile app

 

I've messed with Alodine and never had good luck. Rich is correct on the rear main. There is a 1/4" ledge that can show the way too but I've watched a few blow with the main in upside down.

 

Found out I need new bushings for my rods, which are discontinued, but eBay had them.
Finished the 292 damper besides trimming the snout and degreeing the outside.
Pictures of the drilled flywheel and crank. Starting on balancing the rods.

They were honing a Pontiac 455 SD block, not something you see everyday.

I guess Corona has come to the plains. I have to work from home but I have plenty to do cleaning up our document control for our plant. Still planning to go to the shop every morning to slowly continue, but will need to help watch my 4 year old preschooler.

Sent from my S48c using The H.A.M.B. mobile app

 

Great work, thanks for documenting this build and taking so many pictures.
That would be a great shop to hang around, not many like that left.

 

I am usually bad at taking pictures. Since it seems that GMC information is limited I wanted to be sure to help others if I can, show the insides of an extensive vintage overhaul, and provide a place for me to keep records in the event I forget.

 

Sunnen honing oil makes your hands soooo soft ….

 

I've been saying for a log time that the written information about GMC building pretty much ends with California Bill's book from the early '50s. That was a time before SBC valves and springs were available. The MOPAR rear main seal trick wasn't around as well as many newer ideas in engine building. I'm glad you are doing this and providing details for others. Thanks again.

 

Is this what you are referring to?

 

That deal works on Chevy engines. Not on GMC which seal on the jurnol. I once did a similar deal on a 235 for a local shop. He found a one piece seal that fit in the groove in the block and cap. He said he had to use a grinder and I guess a cut off wheel to sort of straighten out the sides. I turned the crank flange to fit the seal. It was easier that setting up the block and boring it. And we had not seen that done at the time. I never heard any more about it, so I guess it worked OK.

 

I imagine it would take a bit of time to set up the block to bore it for that seal. Rope seals do work if fitted correctly, just a pain to change when they don't. One piece rear seal could probably be done on a staghound GMC block, they have Chevy style rear mains, and looks like 8 flywheel bolts.

**Although I cant see where the seal would go?

 

A friend did one no a GMC about 20 years ago but it was already together and I never got to see it. He just told me it was a MOPAR seal and he had to do some machine work. I have had good luck with the Best Gasket set.

 

ok guys I need some help. The set of rod bushings I bought off eBay was miss boxed and caught by the vendor so my order was cancelled.

I need a set of sealed power 9849 or 9849v bushings. They are listed lots of places but are all "out of stock". Anyone know where to find a set?

Sent from my S48c using The H.A.M.B. mobile app

 

I don't know what a "Staghound" GMC block is. But I believe all the GMC engines I had piloted the flywheel on the crank flange diameter. Leaving no place for a seal, if you made some kind of housing to hold it. My Lotus 907 engine had such a device built in. The high surface speed of the OD of the flange against the rubber seal made for a fairly short service life,

 

Rich, a little known fact I think. Staghound armoured cars were built by Chevrolet with 2 Chevrolet manufactured GMC 270 engines. There is a left and right engine, fluid flywheels. Chevy beefed up the rear main. Not easy to find, but there is one about 10 minutes from where I live. You'd have to buy the whole deal to get the 2 engines! My Uncle was on these during WW2 in the NZ Div. Cavalry, after his stint with the LRDG. https://en.wikipedia.org/wiki/T17E1_Staghound

I found this out from the guy that owns the Taylor Style Special in Perth, Australia. That car runs one.

 

Could you have some made? Aren't they just a bronze bush? I don't know what sort of bronze you'd use. Anyone?

 

I’ve got a lot of supplies but no upper rod bushings. Are you sure they are bad or need replacement. The pin in the piston and thru the rod should have what is called a “palm” fit, meaning you can push the pin thru with your palm. Remember the upper bushing has force fed oil thru the rod.

As for the rear seal it’s a 360 Dodge V8. You need to remove a slight amount from one side of one of them so the part line is not centered on the cap split. You also need a “shim” behind it and a ty-rap size is correct. I’ve never tried it but read some.

 

My machinest says they are bad.

Sent from my S48c using The H.A.M.B. mobile app

 

GMC parts manuals listed piston pins in .002, 005, & .010 oversize at one time. If you had any better luck than I did, you might find a set on an auction site. With your access to the Sunnen pin hone, you're covered. I would venture a guess that one of our piston manufacturers would make a set in any size you need if you're willing to pay. Of course, this will only work if the bushings haven't spun.

 

Found TRW rod bushings this morning on eBay I guess I was dumb and just looked up a sealed power number not the description. Spent the last few day balancing rods. The small end was fairly easy but on the big end, 2 of the rods were much lighter than the others so instead of removing 30 grams from the other rods I welded on the big end of the other 2 to bring the weight up. I got the weights close then resized them both and was again dumb because after resizing they were again lighter. So I lightened the other 4 rods. My 6 rods have 3 variations of rods 5 with the same part number and one with a number I can't find listed Cleaned the block in the solvent tank and got it mounted on the stand. We started a 235 that was traded into the shop, today for a 1954 Chevy truck It is a 57 car engine. Turns out it needs a head gasket and likely a ring job.

Sent from my S48c using The H.A.M.B. mobile app

 

Worked a little today. Rust line on this crank is interesting. Polished the crank then cleaned it up.

Sent from my S48c using The H.A.M.B. mobile app

 

Is welding on rod caps a good idea? Seems to me there would be some stress risers where the weld meets the parent metal. Just a question, never seen it done before to bring the weight up.

 

Neb that’s bad luck on your rods. GMC at the factory matched them very very close with little grinding for balancing. Yours must have not all come from the same engine at the factory. I have a few sets I bought in a package deal from a guy and always kept them wired together just for that reason.

What you had to do scares me and I have no experience with welding on rods with the exception of running a set of Don’s Boxed Rods I bought in the 60’s. The had plates welded on both sides and were really heavy but lived under nitro at that time.