Hi:

- 1989 F250
- C6 AT
- 5.8L 351 Windsor motor
- 282,000 miles.

This is a simple, non-beautiful work truck. I bought it last winter for $1,000. I plan to keep it for a while, but don't want to dump money into it. I won't be putting high miles on it either ... maybe 6-10k per year.

The motor is showing some signs of blow-by (some oil in the air box), and the compression test was around 100-115 in all cylinders.

I'm thinking of doing a simple rebuild ... new mains, rod bearings, cam bearings, rings, oil pump, and re-lap the valves. And of course new gaskets and seals. I'd prefer to not get into any machine-shop work.

What do you think? I already know this won't be as good as a thorough rebuild with all the sweet machining, but I'm hoping it should allow the motor to go at least another 100k or so.

My Questions:

1. - Do you think replacing those parts without doing machine work might actually do *damage* to the motor?

2. - If you were going to do this kind of rebuild, would you use standard-sized bearings, or 10 over sized to fill in the wear from 282,000 miles?

3. - What else would you recommend for a guy in my situation?

Thanks for any help you can provide.

 

Well, your gonna have to take it apart and see what you have. You can't just throw new rings in an engine- the wear over the miles results in a ridge or step where the rings stop at the top of the stroke, and new rings will hit that and break, causing all sorts of damage. You can get a tool called a 'ridge reamer', and eliminate that step. You need to hone the cylinders to give a surface that can break in. The cylinders will actually be TOO smooth now, and the new rings won't wear in properly, causing more blow-by than you already have. Honing the cylinder breaks this glaze, and roughens up the surface so everything can wear in together. But first, you need to measure the bore, since too much slop is a bad thing. I would guess that the bore is too worn to simply hone and put in new rings. As for bearings, if your journals were worn enough for .010 over bearings, it would be knocking like mad. And if there isn't enough clearance, the crank won't turn at all. You can polish the journals and measure them to see if stock bearings will work. There is a product called 'plasti-gage, which you put on the bearing and torque down the cap. How far it squishes tells you how much clearance there is. Your best bet is to pick up an engine book that covers your engine (not a general repair book, but one that deals w/ just engine re-building) and follow the directions for determining the condition of your engine. That being said, the measuring tools you'll need will probably cost too much to be worth it, unless you're going to rebuild more than one engine. An engine machine shop can also measure your stuff and tell you what you need to do. It usually comes down to a decision whether or not to run it as is or spending the money for a full and proper re-build. Anything in between is usually wasted mony, IMHO.

 

Hi FLgargoyle. Thanks for your thoughtful answer. I've rebuilt only one motor in my life, and that was with full machine-shop service. I pretty much just unbolted it, took it to the machine shop, picked it up, and bolted it all back together again with the bearings they provided and parts I shopped for. I was surprised at the cost add-up (it always costs more than you plan for), so I was trying to reduce that cost as much as possible.

I recently put a remanned motor into my jeep, which I bought pre-assembled from a reputable rebuilding shop, and it sure was convenient ... and didn't cost any more than it would have cost to rebuild it myself.

Another question: If the cylinders need to be bored out, does that mean new oversized pistons? Or can you just put larger rings in?

The book was a great idea. Can you recommend a book for the Ford 351 covering 1989?

Thanks for all your help.

 

Usually, if they bore out the cylinders, it means bigger pistons, but they don't cost all that much, unless you're going high performance. I bought an oversize set for a 302 on ebay for $40. I don't know about a book- I have a Ford small block book, but it is way before '89. The basic engine re-building stuff is probably pretty much the same, though. I found that the machinist who does my work gets better prices on parts than I could find on my own, for the most part. He'll need to measure the parts, tell you what oversize to get, then he'll machine it to fit the parts properly. And you're right- you can often get a re-manned engine as cheap or cheaper than doing it yourself. I like to assemble my own, though, just to make sure everything is right. I'm a tool maker by trade, so I can inspect the machine work to make sure it's right. Of course, if you just want to keep the old workhorse going, you can always consider a decent used engine. For me, once I go to the trouble of yanking the engine, I rebuild it so I don't have to do it again.