Should a diesel be longstroke/undersquare?

[Christ]

Originally Posted by rmay635703

I seem to remember an individual I met claiming he converted his metro motor to diesel, he said the compression ratio was high enough to be left alone so long as it was WARM outside.

My estimate would be follow KISS.

Diesels have come many different ways dimensions strokes and compression ratios.

Leave your motor alone, replace the heads to a bit higher compression than you need which tends to hover in the 14to17-1 area depending on how warm it typically is), deal with the less than ideal bowl by placing the fuel intake/"injector" in a "mini" bowl (aka suido precombustion chamber) you bore out of the head and live with the less than perfectness being happy that it works with minimal work. Of coarse you will have to find some very thick heads to fit your unit.

The main issue is getting fuel into the motor at the right time, the rest is moot so long as the block doesn't overheat in the wrong place and break on you.

Good Luck

That's just TOO easy.

It's known among rednecks that any gas engine will run on diesel once it's warmed up, and there have been (failed) engine designs that utilize spark ignition with oil fuels.

I've personally run diesel fuel (and kerosene) through an engine, when I ran out of gas, and it was all I had. There was enough gas in the lines to get it started again, it was already warm, and I just threw a couple gallon of diesel in the tank, and TOOK OFF as soon as the engine started. It ran a bit hotter than normal, but no damage, other than soot in the exhaust and I'm sure some carbon in the engine.

That's a Carb'd 302, though. I'd probably not be as willing to do it with a FI car.

The OEM head on that engine is iron, the block is iron, the crank is iron, so there's the three components that are usable. The pistons and rods, not so much. The pistons won't take the heat for very long, they're thin. The rods are pencils, from what I can remember. They might take the torque, but I might as well just get new ones matched to the pistons. (Maybe I'll try out the OEM ones first, though.)

SO maybe I just need pistons with a higher deck height on the stock rods. I'll have to check the actual dimensions to find out what will really work, though.

The spark plug holes in the head are like 1" long. I was going to hog out about 3/8" into them, then screw the injectors into those holes. They're angled into the cylinders, so they'll still get a non-uniform spray pattern, but it should work out. I won't be able to use glow plugs, though. I'll probably have to start it with some WD-40 or refined oil.

[Christ]

Originally Posted by Old Tele man

...remember, GM "made" their diesel burner engines from basically stock V8 engine block assemblies...and that was why they didn't last (among other reasons).

They used the already butter-like 350 blocks. Those things aren't even close to the 300 inlines, but I see what you're saying.

[JasonG]

Originally Posted by rmay635703

I seem to remember an individual I met claiming he converted his metro motor to diesel, he said the compression ratio was high enough to be left alone so long as it was WARM outside.

My estimate would be follow KISS.

Diesels have come many different ways dimensions strokes and compression ratios.

Leave your motor alone, replace the heads to a bit higher compression than you need which tends to hover in the 14to17-1 area depending on how warm it typically is), deal with the less than ideal bowl by placing the fuel intake/"injector" in a "mini" bowl (aka suido precombustion chamber) you bore out of the head and live with the less than perfectness being happy that it works with minimal work. Of coarse you will have to find some very thick heads to fit your unit.

The main issue is getting fuel into the motor at the right time, the rest is moot so long as the block doesn't overheat in the wrong place and break on you.

Good Luck

Originally Posted by Old Tele man

...remember, GM "made" their diesel burner engines from basically stock V8 engine block assemblies...and that was why they didn't last (among other reasons).

I seem to recall diesels have stronger rods (not a prob as forged rods are readily available for the 300) and stronger head bolts. They should me available, contact Crower Rods, they'll have them.
Think about a turbo to help keep down the smoke, just remember to keep the static CR low.
Yeah those old GM diesels gave diesels the bad name they have here in the states.
Keep us posted.

[Christ]

Wow, there's something I didn't think about - head bolts.

I wonder if grade 10 studs would do it? Maybe I'll just see about using head bolts from some other diesel installation..

Head Gasket -
Should I just toss in an OEM gasket, find one in MLS, or make one from tri-folded 24g copper sheet?

[bbraden]

If you could find a marine head gasket for a 300, that might be a little better. I'm not sure if they're just thicker or stronger or both, but most high performance Cummins running insanely high boost put in marine gaskets and head studs instead of bolts. I'd venture to say that you could get a marine gasket and then bore the holes out for a larger head stud, then put studs in it. You might be okay then as far as the head goes.

Another thing, the first gen Cummins with the VE rotary pump had angled piston faces as well as angled injector ports. The injector does not sit directly on top of the combustion chamber so these maaaay... work in your 300 spark plug holes. That's a BIG maybe though. Any way about it, it's going to take a lot of work.

I would go with a longer stroke, just to take advantage of having the diesel to begin with. I would also go with a direct injection system, NOT an IDI system as was hinted at earlier. Those IDI diesels aren't worth a crap.

If I were you, I would just buy a 4bt or 6bt for cheaper than you're going to fix these 300's, but that's probably out of the picture. If nothing else, I would go buy an old 6bt just as a model so that you would have at least an idea of what your 300 should look like and run like when you're done. Just my two cents.

[bbraden]

BTW, if you have a CR of around 15-18:1 and direct injection, you won't need glow plugs or ether or any other assisted starting until you get around 50 degrees. Under that, you could use a grid heater off of an older Cummins... you should be able to get one cheap that you should be able to fabricate onto it. All it is is a set of elements that the intake air goes through to get pre-heated before entering the combustion chamber. Worked on the older Cummins down to about 0 degrees if you have strong batteries. Anywhere below that, you'll want to have a block heater.

Cummins don't have glow plugs, only grid heaters. I started my '99 on weak batteries (dual batteries) once in 7 degrees and it had been sitting at that temp for over 12 hours. It took about 4 revolutions where as it normally only takes less than one, but it still fired up. It smoked for about 2 minutes, but it eventually cleared up.

[Christ]

Originally Posted by bbraden

If you could find a marine head gasket for a 300, that might be a little better. I'm not sure if they're just thicker or stronger or both, but most high performance Cummins running insanely high boost put in marine gaskets and head studs instead of bolts. I'd venture to say that you could get a marine gasket and then bore the holes out for a larger head stud, then put studs in it. You might be okay then as far as the head goes.

Another thing, the first gen Cummins with the VE rotary pump had angled piston faces as well as angled injector ports. The injector does not sit directly on top of the combustion chamber so these maaaay... work in your 300 spark plug holes. That's a BIG maybe though. Any way about it, it's going to take a lot of work.

I would go with a longer stroke, just to take advantage of having the diesel to begin with. I would also go with a direct injection system, NOT an IDI system as was hinted at earlier. Those IDI diesels aren't worth a crap.

If I were you, I would just buy a 4bt or 6bt for cheaper than you're going to fix these 300's, but that's probably out of the picture. If nothing else, I would go buy an old 6bt just as a model so that you would have at least an idea of what your 300 should look like and run like when you're done. Just my two cents.

Think you can find me a Cummins 6BT for less than $500? The biggest expense is the injection pump, and I'm already considering other options, such as air-assisted injection, which will not require a high-pressure injection pump.

Keep in mind, the idea is not to get the ultimate power or performance, it's just to make a gas engine run diesel with some reliability.

I already know that the 300's stock configuration can handle 500+ lb/ft of torque at higher RPM than I'd want a diesel to run constantly, so the parts themselves should be able to hold up to the abuse - the temperature is what I'm really worried about, which is the reason I'm still considering using the OEM rods as well. I think in this case, the pistons are all I'm going to have to really change before I start working out the logistics of putting diesel fuel where gas used to go, and replacing spark plugs with injectors.

Also - What's wrong w/ the IDI Diesel? International seems to be doing just fine with them...

EDIT: Regarding Ether - I never use Ether in diesels, if I can get away with not using it. I've always kept a can of WD-40 or a similar refined oil on hand, starts 'em up just as quick, but doesn't shock the engine on ignition.

Since I don't use WD-40 for lubricant, because it isn't designed for that, that would be about the only use I have for it, other than water displacement and short term corrosion protection.

[bbraden]

International? They haven't been IDI since 1993. The '94 PSD was DI and the PSD has been ever since. Either way, DI is the ONLY way to go IMO. Starting an IDI in cold weather is not fun at all.

I just think that by the time you spend all that money on the head, including the studs and gasket, then get custom pistons, and pay for an injection pump of some sort, plus the cost of fitting it somehow to the 300, you'll have been able to buy 2 6bt's out of a junkyard somewhere.

EDIT:
Oh and don't forget about the turbocharger and intercooler plus all the cold side piping if you decide to throw one of them on... plus a stout enough manifold to hold it up. It can start adding up really quickly, where as an older 6bt with 350,000 miles on it will still have more life left in it and probably still run cleaner and more efficiently than a home-built gas to diesel conversion.

[Christ]

Originally Posted by bbraden

International? They haven't been IDI since 1993. The '94 PSD was DI and the PSD has been ever since. Either way, DI is the ONLY way to go IMO. Starting an IDI in cold weather is not fun at all.

I just think that by the time you spend all that money on the head, including the studs and gasket, then get custom pistons, and pay for an injection pump of some sort, plus the cost of fitting it somehow to the 300, you'll have been able to by 2 6bt's out of a junkyard somewhere.

That, I can agree with. I'm not sure how much you think I'm going to be spending on the head, though. A new head gasket is cheap, studs aren't expensive either. The injection pump is the most cost-prohibitive part, along w/ the injectors, but I can get IDI injectors from a 7.3 International (From a F-series) for a few bucks a piece, and the injection pump may not cost me that much, either, if I can get one from the junkyard. (Around $30, IIRC.. they have diesels come in once in awhile.)

I'm still looking at the old-school air injected diesel thing, though. I dunno if I can make it work or not, or if I can simplify the design just enough to make it work.

Beyond that, the pistons are the most expensive thing... and with any luck, I'll be able to find 4" pistons in a diesel somewhere that are close to the right specs, and work around it from there. Pistons are also fairly cheap, as long as they're not custom made. If I have to get custom pistons, I'll just wait until I get my mini-forge setup (which could be years, further delaying the project) and cast some myself. (Yeah, I can cast/mill metal, when I have the tools to do it.)

[bbraden]

You'll have to machine a pre-combustion chamber into the head in order for the IDI injectors to work. They're not built to take the hammering that a DI injector will. Plus, you'll have to have a glow plug. I'm betting that with a loose engine and all the WD-40 in the world, it's still not going to start under 30 degrees. I've never actually seen how air injection works... never heard of it before.

Either way, I'm not trying to say it can't be done at all. You can probably do it with enough time and enough money. I guess it's just the German Farmer in me that wants to over-engineer everything. If I build something it's because it's going to be better than I could buy it or so much cheaper that I can deal with all of it's crap that I'll have to put up with.

Anyways, it sounds like you have a pretty good idea of what you want out of this engine, so I'll just leave it at that. Have fun!