Thread: Blown bottom end

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Awhile back I posted some questions about a 350 buildup for a boat. Well everything came out pretty awsome. We stripped an '88 Stingray pretty much down to fiberglass and built a Donzi wanna be. Rerouted 4 inch exhaust out the back. Cut the breather fins in the side. Built an all new interior. Sprayed it white with red racing stripes. I'll post some pics when I get a chance. Anyway we took the short block from an 80 something GMC Jimmy pickup. The cylinders looked good so we made the mistake of just building it up. New heads, agressive cam, torker II intake edelbrock 650 carb. The thing screamed and sounded mean. We were doing a steady 5500 rpm. We then tryed out a more aggressive prop when the oil pressure suddenly dropped along with RPMs. We limped back to our house when it died. It was super hot so we let it cool. It turns over but there is serious resistance. The starter gets hot quick. We pulled off the outdrive so there is no load on the driveshaft and it's the same. I'm sure something gave out on the bottom end. Oil pump pickup? Bearing? My questions are: What do you think worst/best case scenerio is? What should I look for when I pull off the pan? What do you think the cutoff point is for trying to use this block? I'd better off buying a done short block than have to do pistons, rods, bearings, crank ect. right? Thanks for any input. ---Rich

Sounds like you toasted the bearings and probably the crank. Stock chebbies with a bunch of miles on them do not like 5500 RPM in a steady pull across the lake. With any luck, you may have enough left that some rebuilder will give you core value for the short block. If it's all toast, get a crate motor from GM.

hey sorry about everything man. i bet it was sweet while it was running. you might want to check the main bearings and the rod bearings you might of turned them. is the block bored? if the block was bored .060 over then that would be the cut off point for the block. now on the crank if you turned the bearings then you might have to turn the crank .010 to .020 to get it back. i hope that this helps. is it a two or four bolt main? hope this helps some

Cd

Fun doesn't do it justice. I've had an ear to ear smile for weeks. This thing was a total junkyard dog. We really made it flat out haul and look good too. It was christened "Full Throttle". We are now changing it to "In Too Deep". I'm figuring everything on the bottom is smoked. It is a 2 bolt. I don't think it's been bored but without measuring who knows. I'm pulling the engine Friday. When I pull the pan off will it be pretty obvious? What should I look for? Rough surfaces? gouges? Will the bearings just be falling apart? I've never messed with the bottom end before. I guess that is why we took the shortcut in the first place. Will I be able to tell anything without taking it to the machine shop? The mechanic at the service station down the street has a clean 305 ready to drop in. The crank is polished and balanced. It's dynoed at 330hp. It only has a few thousand miles on it since he built it. He went with a bigger engine in his firechicken. I'm trying to get it for a grand. Then I can worry about the 350 in the winter. Oh and that 5500 was in the ocean. No flat water to be seen. I suspect it was a combination of the weak bottom end and the aggressive pitched prop which got that boat completely out of the water. When the prop had no load, I wonder what it momentarily spun up to. The torque applied when it caught again can't be good either. Maybe a rev limiter in Version 2? I've been thinking about getting the pickup welded so it doesn't move around along with a deep sump.

If it's a virgin 2 bolt with a spun main, you'll probably have to do a line bore to repair the block. Half of the cost of upgrading to splayed caps is getting the line bore, so I would upgrade to splayed caps while the thing is apart. Then, rebuild away, there shouldn't be any other damage to the block.

Will I need to recondition the crank? If I do the splayed caps and a line bore will I need to do any other machine work? Will they hot tank it? I'll probably bore the cylinders or at least get them honed along with new pistons and rings. What do you think the machine work will run? I still wonder if it makes more sense to get a done short block sent out. ---Rich

Your crank will most certainly need to be turned, if it isn't damaged so badly it's unusable. Otherwise, do a standard rebuild, bore the block, deck it a little, get new cam bearings, freeze plugs. A good balance of the rotating assembly is a necessity at those rpms and you may want to consider switching to solid lifters.

When you get that sump pan off, first thing to look for would be discoulored con rods. If they're heated up to a nice bluey coulor, theres your spun bearings.

How to make your next motor have a better chance of survival?
Performance build the bottom end, good quality rods and rod bolts with correct bearing, side thrust clearances and crankshaft end play clearances should be MANDATORY.

You have'nt mentioned how the prop shaft is connected up to the engine, but it appears to me with what you say about it being a used motor the crankshaft end clearances may have been a wee bit bigger due to age, and as you say with the baot skipping across the water and the prop biting in the load could be shoving the crankshaft forward in the block and putting side thrust on the con rod bearings. Combine that with the motor over reving with no load and it's a case of bye bye motor.

Most reliable and cheapest rev limiter I can suggest is a single point distributor, set the spring tension on the points so when the engine over revs you get points bonce thus a crude form of rev control.

Well...the 305 down the street was sold so I'm now looking for a short block assembly. Anybody have any experience with Larrys Performance I've seen em advertise in the back of Car & Driver and Chevy High Performance mags for awhile. They seem to be the cheapest. I'm looking at the 383 4 bolt One piece seal with just the Kieth Black forged Pistons, moly rings, crank, oil pump, rods and bearings. not assembled for $1200. Everything else is all new from the other engine. I have to check if the cam bearings and freeze out plugs are in. Any thoughts? Oh and cooling isn't a problem. Water in these isn't recirculated. It actually runs pretty cool even at high rpms. Well as long as oil is pumping.

Check EVERYTHING, probably pumped metal particles all through the engine.

Your gonna want a motor that will rev safly to 6500 at least, it dosen't matter how much power it has in the water just high Rpms, our boat has a 488 Mercruiser I/O and it has 185 Hp and revs at about 4800 at 40 MPH ( top speed( 23' glass cabin cruiser boat ). you just need somtin that's gonna take the revs, boat's do rev that high, it's not unusual.

Do you have a heat exchanger or do you just pump sea water into the engine? The heat exchanger is a radiator sort of with antifreeze mix in the middle conpartment and the outer wall has a compartment that sea water pumps through to cool the antifreeze.