hi everyone,

i have heads, crankshaft and camshaft from a 76' 350 engine. ( parts that comes from failed restoration of my 76' caddy seville ).

in france we have many olds cars with 350 diesel ( more than gasoline ).

Can i rebuild an engine with a 350 diesel block ? need other parts ?

best regards.

 

Yes you can use the block, and change it to gas.

 

Sorry, more info, you will need different heads, and intake manifold,Maybe pistons, are the big items, there may be other small things, not sure what?

 

If you have a good diesel engine, as said your current 76 #8 heads will work well with the flat top pistons, will put you close to 9 to 1 compression with regular replacement head gaskets. I believe the mechanical fuel pump eccentric needs added to the cam gear from your motor. Is diesel block cut for a mechanical fuel pump? I believe some grinding is needed to fit a gas timing chain but is a good idea as better quality timing sets are available and the diesel is different due to the injector pump. A few have done the conversion. Don't push the rpms very high, the diesel reciprocating assembly is very heavy. Good luck.

 

When the Olds diesels were new, Mondello sold a conversion kit to turn them into gasoline engines. Basically you need to change cam, heads, and intake, and add a distributor and fuel pump. The Olds diesel block maintains all the features necessary to do this, including the provision for the distributor. The diesel pistons, while heavy, will work with the gas engine heads. You may want to get the large chamber no. 8 heads.

 

Does the injector drive hole need to be plugged? I've never done it, but I thought there was one block modification that had to be done.

 

If you mean the hole to drive the injector pump, no. It is simply an opening between the valley and the timing chain area inside the front cover. Both spaces are already connected anyway.

 

Joe, can the diesel cam not be used? While not ideal, it is usually a roller cam, most out there will be DX roller cam replacement motors. That means more dollars to replace.

 

i thought that a flat piston on this block could give a 11:1 compression

i have kept camshaft, crankshaft, heads, timing chain and some other part from my RIP 350 gas. It will be easy to rebuild another engine, maybe juste honing the diesel block ( aviable heure : https://www.leboncoin.fr/vi/1050564928.htm ) it could be possible to import a short block from usa but it will be expensive due to weight ( a diesel complete engine.
it seems diesel and gas have same bore and stroke.

- can i install my crankshaft from gas block to diesel block ? same main bearings ?

- on several website i've read diesel block have hardened alloy. it heat more slowly. any know issues about that ?

i've found mondello book on olds v8, i'll probably buy it.

best regards

 

Yes, the same bore and stroke. Shorter rods and taller pistons. The crankshafts are different, the diesel has 3" mains and the gas has 2.5" mains. With your #8 heads, which have a big chamber, it will give 9 to 1 with the flat top diesel pistons. Early heads would give 10+ to 1 compression.

 

The factory W31 motors with flattop pistons and 64 cc heads had 10.5:1 CR. Use no. 8 heads with 80 cc chambers and you get a reasonable CR.


Correct

No and no. The diesel crank uses 3" main bearings, same as a BBO. You can buy bearing spacers to run an SBO crank in a DX block.


News to me.

 

That Mondello kit was over $2500 and you still needed a ton of machine work done to the block and that was back in the late 80s early 90s. The kit came with a custom crank and .125 over pistons custom length rods. Then you needed high flow heads that Mondello custom made, probably about $10k when all said and done. A lot of money back then.

 

No, that is NOT what I am talking about. This was NOT a kit to build a race motor. It used the stock diesel rotating assembly and required no machine work.

 

I believe you need to machine some of the fuel pump injector area. As well the cam area on the block or spacers for the timing gears. Spacers for smaller diameter crank cost about $600.

 

Interesting that there was a diesel to gas conversion kit.

Here's a good thread on the Oldsmobile diesel.

https://classicoldsmobile.com/forums...-350-a-112541/

 

You all need to work on your reading comprehension. I'll type more slowly this time, maybe you can follow along. And thanks Jesse for finding that old thread.

One more time: I am NOT talking about building a high performance motor from a diesel block. Back in the mid-80s there were a lot of nearly new Oldsmobile diesel cars with blown head gaskets. Owners were fed up with the diesel package but couldn't afford to dump their cars at a loss and didn't want to spend a ton of money replacing the head gaskets just to keep the crappy diesel. The kit Mondello sold was designed to convert the diesel motor to gas power with a minimum of effort. This was NOT intended to be a drag motor, simply a cost-effective package to keep these cars running for a few more years - at least until the payments were over.

The beauty of the Olds diesel is that it shares nearly all of the architecture with the 350 gas engine. If you need to pull the heads to replace the head gaskets, then simply replace the diesel heads with gas heads. The 80 cc number 8 heads (which were very plentiful in the mid-80s) yield a 9-something CR with the original flattop diesel pistons. Yeah, this is a very heavy rotating assembly. Who cares in a luxo-barge that will never see over 3500 RPM? The Mondello kit included the gaskets and a special gas engine cam that replaced the diesel cam. You do NOT have to machine anything if you simply use a stock timing chain. Retaining the injector pump drive gear on the front of the cam spaces the timing chain out to clear the boss - machining is only required if you want to run a thicker double roller cam. The stock diesel crank doesn't require spacers. The block doesn't even need to come out of the car. Now just replace the lift pump and vacuum pump with a gasoline fuel pump and distributor, bolt on a 4bbl intake and carb, and off you go. Yeah, you have to flush the fuel system before you put gasoline in it. Done.

 

I wonder if Oldsmobile ever released a TSB to dealers telling them to use the Mondello kit on customer's cars that had reoccurring blown head gaskets? Or was the Goodwrench diesel engine GM's only answer to poorly designed diesel engines?

 

If they had, the parts would have been given GM part numbers and would have appeared in the parts books, so I'm guessing not.

 

I would think the dealer would have installed a whole new engine. I wonder how many gas engines GM installed for free.

 

Didn't think of that. It'd be quicker to swap an engine vs. removing the heads and replacing a cam.