The Stovebolt Site Forums The Shop Area Engine Shop 250 do's and dont's...?

Hey all, I'm back with a 250 question. My dad has a fishing boat he keeps in Kodiak Alaska with my brother that has Mercruiser 165 (Chev 250 I-6) Before he sent it up he replaced the rotted out 250 with a early 80's Camaro 250 that was "rebuilt" Last week while heading out of the harbor, the 250 started knocking, and to make a long story short, the #1 cylinder wrist pin is siezed, and the # 1 cylinder is egged. The island machinest says that the block was bored incorrectly, since the engine only has roughly 50 hours since "overhaul" He says that the block is shot, and that thay need a new one. I am planning to pull my 68 250 out of my project truck, and do a short block on it, as it sis run good, but want a fresh bottom end to ship to the Island within thenext 2 weeks. Questions are, once the engine is out, what is the best way to check the cylinders and journals to see if I can just hone/re-ring and re-bearing, or if I need to get a machine shop involved...
The machine shop here in Washington state claims that timing and too rich of fuel (too much fuel) cause the #1 cylinder to overheat siezing the wrist pin, and trashing the cylinder. Is this a possibility on the 250??? Doesn't sound right to me, and I have been around cars and mechanics all my life...
My brother and I are trying to help out my dad by shipping my 250 short-block via barge to Kodiak, which is expensive to say the least, so I am trying to save $$ on my end for the short blocking of my 250, and I'll worry about finding another engine for my project for later. I have a hone, and I've gapped rings and done crush strips before, any other pointers or tips would be greatly appreciated. PS the boat is a 1973 and the original I/O mercruiser was all 1973 if that makes a difference.
Thanks, Garry K

The #1 cylinder problem has happened 3 times on one I've been working with, still don't know why! I helped assemble one another shop had machined, and it scored the #1 piston and cylinder in about 2,500 miles. We tore it down, sleeved the cylinder, installed a new #1 piston, and reassembled. Scored again in about the same time frame. Got another block, different pistons, 307 V-8 flat tops this time, and it's knocking again! Also, the replacement block we got had massive wear in the #1 hole, and had to be sleeved. It looks like there's a cooling or lube problem on at least some 250's at the front. Anybody got some words of wisdom?
Jerry

I have only worked on a few of them so I haven't seen a pattern. I do know for a fact, that if you torque the front left head bolt to much, you will break the corner of the block off! It cost me a second block...

It sounds like you all ready have a good plan on the rebuild. Go ahead a hone the cylinders a bit to knock the glaze out, then find a machine shop willing to measure the bores. Might as well take the crank along with you if yo don't have a good micrometer.

Joe

OK, I have the 250 out of the truck, down to basically a short block. Cylinders look very clean, though pretty "polished", and not even enough of a ridge to catch a fingernail on. Will drop the rod and main caps tomorrow to check the bearings and journals. THis is a budget short block evolution, but does anyone see any problems with just a hone job, fresh rings, fresh bearings, and clean it up real good and asseble with fresh gaskets? The cam lobes look barely broke in, as they are more "rough" than "polished". lifters are nice and flat. No sign of any play in the timing gears. Oil pressure was good before the tear-down, so pump should be good??
Any opinions greatly appreciated.
Garry K

I had a similar rebuild on a 292. It was in basically the same condition as the one you describe. I honed it litely and put a stock rebuild on it. I have driven it for the past 20 years without any head heating or wrist pin problems. Hope this gives you some feeling of relief from worry. Have a good rebuild, it's a Chevy!

I drove my Dodge 318 100,000 more miles after hone and rebearing job. At 200,000 the pistons were slapping a bit, but still ran strong. Joe