crank grinding/lapping O/D hone idea

[squarebody]

If this is in the wrong place can a mod move it for me.

I google the hell out of this and searched here specifically with built in search to no avail on my specific idea.

So I tried one of those one piece oil pan gaskets after swapping to a high volume oil pump and got the wrong one for my engine, my '86 c20 has a 73 350. Anyway the front seal was too thick and on the 20 mile test drive I didn't notice as almost all of my oil escaped. long story short I spun a rod bearing. while I can use a local machine shop I always like trying diy first. i have heard of the sandpaper trick both using a shoestring and just clamping the paper in the rod and spinning it with the starter. However I had what I think may be a better idea, take 4 hone stone cut to the right length to match the journal and mount those on springs in an enclosure that clamps around the journal in question then the whole assembly is rotated either directly by or on a belt driven by a stepper motor.
O.k. napkin/spare printer paper cad time.
so the only thing i didn't think of before i started drawing, was the spacer which would be made out of something like delrin, nylon, or brass and be to prevent unbalanced loading of the stones.

I will work on a 3d model to make a printed test prototype and upload the stl files or link to them if that wont work. I have a graveyard shift tonight so I'll get started on it from work tonight

in the mean time what are your thoughts? Is it rube goldberg enough or just crazy enough to be a possible fix.

 

[txvwnut]

They used to make in-the-block crankshaft grinders back in the day. The big problem with those and the whole process was it would not get the journal eccentric and sometimes they would get the journals out of synch or time with the other journals and then you ended up with a vibration that you couldn't get out until you ground the crank on a proper machine.

 

[BillK]

If it actually spun the rod bearing in the rod then the rod is junk and the crank needs to be reground. Period I have been doing this for 30 years and have NEVER seen a spun bearing that did not require the above.

Keep in mind that the tolerances for crankshaft bearing journal size are typically less than a thousandth out of round, straightness and size. You also have to figure out a way to keep the stroke correct

 

[squarebody]

Not what i wanted to hear, but it makes since. Think something like that would work on extremely light scratching?

oh couldn't sleep so here is a mockup without proper measurements

 

[homebuilt burner]

Tried to polish a crank in a Mack truck once. It worked for @ 5 miles. Then the damage was worse. I would bite the bullet and pull it out and do it right.

And generally I am a DIY guy also. If it works I'd like to se pictures of your setup.

 

[squarebody]

Well i start half a month of vacation tomorrow, and we only have plans through the middle of next week so maybe I'll have a machine shop fix my crank and rod or just replace the rod and grab a crank that needs work from a salvage yard and experiment on that.

I also have a spare set of heads that are a diy experiment,no cracks and straight, just need cleaning and valve work really. but thats for a different thread.

 

[2oolhound]

food for thought -

Here's the pro final polish tool that's been around forever. They typically use old old 400 emery that has worn down to be about 1000 grit emery.

 

[squarebody]

I have seen the professional polishers, and the sandpaper, but the 9' shoelace gives me an idea. You know how 8-track tapes are an endless loop with a single drive, find a long cotton loop, wrap one end multiple times around the crank and attach a motor... I honestly don't know why the first thing I always think of is how to automate things.
Either way I'll post pics of the damage when we get back from camping I'm not dropping the pan until i have time to work on it weather has been too bad to leave my truck with the engine open and it only half fits in my garage so i can't leave it inside. I'll still have 10 days when i get back.

 

[sberry]

There should be a learning curve here,,,, don't fuk with stuff not broke trying to "make it better". What was the point of the hi vol oil pump,,,, was an attempt at saving the engine? How did that work out?
Good lesson,,, where doing nothing would have been an improvement.

 

[squarebody]

actually it was a faltering oil pressure and a leaky pan gasket that prompted the change, however i could have left the old pump in when i realized it was just a clogged screen (clogged with rtv from the previous owner). either way pan off would have ended up with wrong gasket as i needed a pan gasket for 73 and i asked for one for the year of the truck 86

and i did say i would get it fixed the right way, after the second response see post #6. The rest of my posts were ideas and just my mind being over active.

 

[squarebody]

Anyway I should have included the reason for the pump swap in the first post low oil pressure. 20psi at idle cold ~2psi at idle warm and 15psi at 3k rpm warm. That was at 4000 miles past a rebuild if the previous owner could be believed + my 1500 miles or so pressure didn't start acting up until about 500 miles or so back.

 

[ttpete]

Anyway I should have included the reason for the pump swap in the first post low oil pressure. 20psi at idle cold ~2psi at idle warm and 15psi at 3k rpm warm. That was at 4000 miles past a rebuild if the previous owner could be believed + my 1500 miles or so pressure didn't start acting up until about 500 miles or so back.

That's when the RTV the idiot used finally got to the screen. A shade-tree "mechanic" strikes again.

Seeing that it's got to come apart, you could always dig up a 400 crank and make a 383 out of it.

 

[squarebody]

I could... ... i should have torn it down and checked through everything and put shellac on all the gaskets that needed it after the first problem. I bought it with "roughly 3k on a rebuild" it wasn't timed quite right when i drove it home, random misses etc but not bad. A friend of mine that has been messing with sbc's for the last 30 years or so said check rockers after we couldn't straighten it out with a timing light , I did and found about a third had their nuts bottomed out. he said the lifter were suspect and suggested to me to go ahead and swap all the lifters. After that it ran great until the oil pressure problem, which led to this. hopefully I can get by with just having the crank fixed and replacing the rod.

 

[sean Buick 76]

Personally I would have a machine shop mesure the main and rod journals of the crank and also the inside diameter of the rods and mains. If it is in spec then just do new bearings and a polish on the crank but 95% of the time a re grind is the best bet. It's low cost to have the crank cut, not worth the risk.

Regarding the leaks I bet you have a warped oil pan from someone over tightening it at some point.

 

[squarebody]

I peened the holes with the one piece gasket and again with the one that's on it now this one hasn't leaked a drop so it is or was probably warped. Every time i think about a new pan i think about going with a cast pan just so i don't have to worry as much about warping and having to peen old holes or load spreading then i read all of the horror stories about cracks and road debris making new oil drains and I change my mind.