When to rebuild vs overhaul

[wdills]

I have my 289 torn down and was taking some measurements this weekend. Before tearing the engine down, I did a compression test and all cylinders were between 150 and 160 psi. The tear down was due to a knock.

The knock turned out to be from a couple rod journals that are in very bad shape. They would have to be welded up and turned back down to save this crank. The cost of that is only $10 cheaper than buying a NOS crank so I plan to buy a new crank.

The pistons and cylinder walls look great, no scratches or pitting and no ridge around the top of the cylinder. The cylinder bores all range from 3.568 to 3.570 so they are about 0.007" over which tells me wear and not a previous bore. Not sure where the ridge at the top went, maybe it was cut away during a previous overhaul.

I measured the pistons around the skirt at about the pin level. They were all either 3.557 or 3.558 diameter. Is this the correct place to measure piston diameter?

The math tells be that with the wear to the pistons and the wear to the cylinder walls, I have about 0.005 clearance between the piston and cylinder wall all the way around. Or about 0.010 total clearance if the piston is up tight against one side of the cylinder wall.

Does this amount or cylinder / piston wear call for a rebuild or does it just need a cylinder hone and a new set of rings?

[(S)]

measure twice cut once

Make sure to use a bore gauge (taper gauge)

If you cut any ridge and hone a cylinder to replace rings, you'll lose up to .005 so be sure to measure carefully. I have done this and had the (largest cylinder) bore measure .009 oversize when done. It is not recommended but it was done per the customer. Your engine is too far out to do this, you may end up at about .015 even if you are carefull.

Think of it this way: the engine you have ran many miles and put the cylinder 'out' of square so if you do not square it up, the next overhaul will be required that much sooner. (and there is no 'formula' to figure out when it will start slapping, and blowing smoke.....

[irish]

As an engine rebuilder by trade, I can tell you based on your compression ratio's and measurements a honing and rings are all that you need, but alot of people will tell you with those measurements you should bore it out for oversize pistons, in my opinion that would be a waste of money. Also you should know that buying a NOS crankshaft is not necesarily 'plug-n-play', even a NOS crank can need to be turned, they aren't always 'straight and true', sometimes they have surface rust etc. Hope this helps.

Joe

[Mike Van Veghten]

All due respect...

As has been stated, FIRST, to get accurate bore dimensions, a bore mic (gage) NEEDS to be used to achieve accurate bore dimensions.
These need to be taken at four places up and down and as measured on the thrust side of the bore.

Then, there is only one location to measure a piston, 90 degrees from the pin bore length and at the center of the pin centerline.

Now, all that said...if you still have a .010" piston to bore clearance...."yes", replace. That's way too much for a stock cast piston. And honing for fresh rings will make that clearance worse.

So...first...correctly measure the bore and pistons and make a new decision from those findings.

Mike

[PackardV8]

What are your goals for this engine? How many miles and years do you expect it to last? If you expect your grandchildren to be driving it many years and miles from now, rebuild it. The cost will never be any less than right now while it is all out and apart.

I rebuild Studebaker and Packard V8s in a small way. You know I'd rebuild it if it were mine. However, look at your budget. If it is an occasional/weekend show car which won't see a thousand miles a year, if you plan on selling it someday, then re-ring it. The compression is better than most Stude V8s. A touch-up with a dingle ball hone won't remove any more iron. New rings, a couple of rod bearings, a gasket set and you are good to go.

While the heads are off, have your machine shop install positive valve stem seals. The OEM valve stem seals were ineffective, if they are not gone completely and are responsible for most of the oil burning which give Stude V8s a bad rap.

Send me your junk crankshaft. I'll see what it will take to bring it back. If it can be fixed at a reasonable cost, I'll split the profits with you.

jack vines

[wdills]

The car will be an occasional weekend driver and go to a few car shows a year. Definately not a daily driver. I just called a few machine shops and their price to bore the block is a lot less than I expected. For the price they quoted and a set of pistons I guess I will go ahead and have it bored out.

Jack, you suggested using a positive valve stem seal because the OEM design didn't work so well. I buy most of my parts from SI. Do they provide the OEM style or the good ones? If I need to get them from somewhere other than SI do you have a source and part number. I certianly don't want smoke when I am done.

Thanks to all
Wayne

[DEEPNHOCK]

Save the bad crank!
Sell it to someone as a core.
Someday that will be all we can get!

[PackardV8]

The Stude uses 11/32" valve stems and the positive seals are just the same ones Ford and Chevy V8s use. They require the outer diameter of the top of the valve guides be cut to proper size to receive them. Any automotive machine shop can cut the guides and install the seals for you. It only takes a few minutes and they'll have a box full of seals. They buy them by the gross. Absolutely nothing rare or trick about it.

Too bad you are so far away or I'd give you a bid on building your engine. Although, right now, we're building a mild performance Packard V8 for a guy in Georgia.

jack vines

jack vines