The Stovebolt Site Forums The Shop Area Engine Shop I think I have a spun bearing on my 261

I have a 1946 2 ton with a 1958 261 (Block Serial Number - 3759365)
I drove it yesterday about 50 miles on the freeway and watched the oil pressure drop slowly the whole way.
When I finally arrived home it was zero.
It never knocked really bad.

I put on another oil pressure gauge and it also registered zero. Normally it pegs the stock 30 lb oil gauge in the truck.

I disconnected the gauge and just had the oil line exposed. It was spitting oil and air but never really poured out oil. The dip stick read full.

So I pulled the pan today. There was a lot of metal in the bottom of the pan. I guessing I have spun a bearing, but have not disassembled to fully diagnose.

Here is a short video of my oil pressure while I drive
https://drive.google.com/file/d/0BzghoG21YVYEeUxyR1k5X2VyelFfWlF2a1g3dFU5eUJSRjVv/view?usp=sharing

I have a couple of questions:
1) If I need a new crank, the casting number 3701488 fits 1953 - 1962 Chevy 235 & 1954 - 1962 Chevy 261. Does anybody sell new cranks?
2) Im seeing a few folks who sell remanufactured ones. Are these OK?
3) Since Im rebuilding, I also had a compression question. I have an 848 head on this engine, most cylinders are about 150PSI, but 2 are at 130PSI. Is 150 what I should be expecting?

Jay, since your in the BIG state I would think there is a shop close by that can diagnose your crankshaft for you. Perhaps it could be polished or if never turned, maybe it could be turned maybe 10 thousandths and be just fine. I'm lucky as I have Spartan Crankshaft just a few miles from my house. I'd probably trust my own crank, and my own local guys, more than a reman.
I had a spun bearing in my 261 and the crank polished out nice. Hope your as lucky.
http://i140.photobucket.com/albums/r19/LutherParris/1950%20Chevy%20Coupe/Enginepictures007.jpg

While you got the head off be sure to check the '848" head to be sure the coolant holes to match the ones in the block between each set of cylinders.
I don't know about the compression but what your stating doesn't sound to awful bad. Its not like you lost half of it or more.

Sounds like you had an oil pump to maybe die on you??? Clogged pickup screen??

You can find info your looking for here.
http://chevy.oldcarmanualproject.com/

How long ago was the engine rebuilt? If that is unknown or many miles ago, and given that a 261 is a highly desirable engine, I would do a complete overhaul of everything. It is a pretty big chunk of change, but if you have it done, you will never regret it. All new stuff is a great piece of mind.

You have a 13.3% difference between the highest and lowest compression in your cylinders, which is excessive.

You may have a spun bearing which has scattered bits of bearing material throughout the engine which must be removed before more damage can occur.

It will be a lot of work to remedy just these two issues so you may as well go for the gusto and do it right.
Carl

Strip the block down to bare bones, including removing all the oil gallery plugs. Failed bearings put metallic debris all through the engine, and it's essential to get all of it out. I use a set of rifle brushes through all the passages, followed by repeated flushes with a pressure washer. If there's a local engine rebuilder or automotive machine shop handy, get them to power-flush the block after removing all the parts, including the cam bearings.
Jerry

lI will update the thread with what I find, but I agree with Hotrod Lincoln and 52Carl that a full overhaul is needed. The magnetic drain plug had a bunch of stuff stuck to it, and the small amount of sludge in the bottom of the pan looks like metallic paint. There are some fairly large bearing chunks as well.

I dont know why the difference in compression exists, but I agree it should be addressed, and at a minimum I will hone it and put new rings in it. I will have the head checked out as well.

The sad part is that this was rebuilt only 3 years ago and has less that 10k miles on it. Oil got changed religiously with Brad Penn 20-50.

I haul things quite often, I was delivering some large trees when my engine failure happened, but not super heavy things.
https://drive.google.com/file/d/0BzghoG21YVYEZ29EbTZ0YkJIWTFOZnJVd3F2cnctVjB2bkFF/view?usp=sharing

A specific compression number isn't important, as 3 different gauges used to check the same cylinder will probably give you 3 different pressure readings. What is important is the percentage difference between cylinders, which should be within 10%- - - - a sub-5% variation is better. Sometimes something as simple as valve adjustment or a temporary buildup of carbon in the combustion chambers can make a measureable difference. It takes a couple of tablespoons of carbon to change compression pressure noticeably. The camshaft profile will also make a difference in measured compression, no matter what the theoretical ratio is.
Jerry

Just saw the picture of your truck. What a beauty! It deserves the Full Treatment. Sounds like you ran into some bad luck, or somebody missed something on the rebuild. I hope that you can determine what caused the catastrophe upon disassembly.
Carl

Here is some pictures of the engine teardown
Mains look pretty good - https://drive.google.com/file/d/0BzghoG21YVYETTlwcktldjByczg/view?usp=sharing

Rod bearings are very bad - https://drive.google.com/file/d/0BzghoG21YVYEOWFCRlljVDdnNEk/view?usp=sharing

Broken lifter - https://drive.google.com/file/d/0BzghoG21YVYEbWdXZkFncEhXSmM/view?usp=sharing

Bad Piston - https://drive.google.com/file/d/0BzghoG21YVYEZkpDLVFQR2JTcU0/view?usp=sharing

Since the damage gets progressively more severe the further from the oil pump you go, I'm going to suspect there's a partially-open relief valve in the pump. That would explain why the main bearings were not severely damaged- - - -they get lubed before the rods, which are at the end of the pressurized oil system. The piston probably galled due to insufficient oil thrown off of the rod bearings and little or no oil coming from the spit holes in the connecting rods to the cylinder walls.
Jerry

Jay Brown,

I found ( 1 ) GM NOS Crankshaft

GM part # 3701486 with casting # 3701488

@

NOS Parts Source
Olathe, Kansas
phone: 913-220-5746

I'd be interested in how much he wants for it.

You can always make an offer.


Denny Graham has a full set of (12) GM NOS

solid lifters GM # 3836342 that you might be able

to get him to sell to you. I know they are in mint

condition.

Here's a photo of the lifters Denny has.

http://i669.photobucket.com/albums/vv57/glp0329/3836342/261_Tappets_GM_3836342__zpskdvccbok.jpg

NOS Parts Source

has (1) GM NOS Lifter - GM # 3836342

Collectors Auto
Oroville, WA
phone: 800-414-4462

has (2) GM NOS Lifters - GM # 3836342


What's the part # of the GM NOS oil pump that

you'll probably want ? I'll see what I can find.


I'm not 100% sure on this part #...but it might be

correct. GM NOS oil pump on ebay.

http://r.ebay.com/MQc8aT


Check out this re-manufactured Crankshaft

http://www.northernautoparts.com/part/ck-18005


George
'54 3600

I don't think the lifter top coming off is a big deal. It just needs to be replaced.

Thanks for the info!

Unfortunately my parks book stops at 1949, so I dont know the part number for the oil pump. My engine is a 1958. Block Serial Number - 3759365

There is a new Melling M-45 pump on Ebay right now for $123.00 with free shipping. Things don't get much better than Melling- - - -I used them on my race engines for 30-something years.
Jerry

I think I figured out why my engine was starved for oil. check out the picture of my oil pickup. it has a hole in the top. When I took the engine apart, the pickup swiveled up and down. The only thing I can think of is that it hit the crank or a rod.
https://drive.google.com/file/d/0BzghoG21YVYEazFCQkNkaU9YODA/view?usp=sharing

My 261 engine is now rebuilt.
40 thou over on the pistons and 20/20 on the crank.
I finally got the pin pushed in so the engine will be full flow thru a filter.

https://drive.google.com/file/d/0BzghoG21YVYEU1J3MmxoVW51QTQ/view?usp=sharing

https://drive.google.com/file/d/0BzghoG21YVYEb1lZTHVnczVTVlk/view?usp=sharing