Early Revcon Diesel Swap

[FEF]

All,

I've got a 'flat nose' Revcon 250 (not GMC) motor home. It uses the second generation Toronado drivetrain, with the Olds 455.

The first question I have is, of the 6.2 or 6.5, which has the least amount of electronics? I'm not afraid of ECU's and sensors, but I'm trying to keep the engine as simple as possible. Do I have any other options, If I'm looking for an engine that's more mechanical by nature?

Assuming it turns out the 6.2 or 6.5 is actually a good idea, it appears I can easily bolt the GM block to the BOP bell housing, with an adapter plate. What I don't know is if the GM converter will slide into the Toronado chain drive unit. The TCI site makes me thing it will bolt right up. I'm not so sure.

What about engine mounts? Are the engine mounting points on the 455 and GM diesels (GM small block?), even close? I don't know anything about the Chevy/GM/BOP differences. Though, the pined thread tells me about the high points of the 6.2/6.5 engines.

The brakes, alt, AC, and all that other stuff, will be pretty easy, after I get the engine mounting details ironed out. Time consuming, but less of a worry, when compared to the engine/wiring details

It's a great tip to buy a diesel whatever, and do 2 swaps. If done right, I might get quite a bit of my money back. Excellent idea, indeed.

Great Forums. Thanks in advance for the help

[BigRabbitMan]

FEF,

Good to see you looking at a diesel conversion to your motor home. I am also and my info is posted in the thread about "converting and early 1976 Motorhome". As you can see mine is an FMC, another of the classic older motorhomes. I came close to buying a Revcon. Great coach. Good luck on your conversion and I hope your questions get answered by those that have the information.

[convert2diesel]

If my memory serves me correctly, the Toronado/Eldorado setup used the THM400, thus the 400 torgue convertor is a straight bolt up if you used the 6.2/6.5. As far as the mounts are concerned, if you can find a late 70s early 80s olds 307 or 350 diesel, they used a motor mount relocation bracket that allowed them to install these engines into any "A" body car or truck. Perhaps this bracket could be used to reverse the process and when used on the SBC configuration it might marry to the BOC mounts. Just a thought.

Another thing you should consider is the use of the 12 valve Cummins, assuming you have the room. This has a mechanical pump and fuel delivery and are reasonably simple to work on. Do a search on this board as this is a very popular conversion. The 6BT and 4BT were used extensively on delivery trucks (Frito Lay) with the THM400 tranny. The adapter plates are readily available (though this configuration may still reguire the BOC adapter as well) and there is lots of stuff available to add power to these engines. Would have to fabricate your own mounts and probably have to play around with gearing but it would seem to me that it would be a better engine to use for this application.

Keep us posted.

Bill

[convert2diesel]

If my memory serves me correctly, the Toronado/Eldorado setup used the THM400, thus the 400 torgue convertor is a straight bolt up if you used the 6.2/6.5 (get the one specific to the diesel for stall speed). As far as the mounts are concerned, if you can find a late 70s early 80s olds 307 or 350 diesel, they used a motor mount relocation bracket that allowed them to install these engines into any "A" body car or truck. Perhaps this bracket could be used to reverse the process and when used on the SBC configuration it might marry to the BOC mounts. Just a thought.

Another thing you should consider is the use of the 12 valve Cummins, assuming you have the room. This has a mechanical pump and fuel delivery and are reasonably simple to work on. Do a search on this board as this is a very popular conversion. The 6BT and 4BT (commercial versions) were used extensively on delivery trucks (Frito Lay) with the THM400 tranny. The adapter plates are readily available (though this configuration may still reguire the BOC adapter as well) and there is lots of stuff available to add power to these engines. Would have to fabricate your own mounts and probably have to play around with gearing but it would seem to me that it would be a better engine to use for this application.

Keep us posted.

Bill

[kaylabryn]

Little info that I know is that the older first generation TH-400's (you have a 425 but they are pretty much identical only different haha" the torque converters were interchangable and I doubt that GM changed that. This is back when GM cared. Here is some links for information about your transmission and some upgrades you might consider while doing the coversion, especially the Switch Pitch portion, I have had a few older Eldo's and it makes a world of difference at both spectrums power/economy.

http://www.remaker.com/caddy/survival.html "Scroll down to the SWP portion"
http://www.california.com/%7Eeagle/SWITCH.html
http://www.bdub.net/tranny/index.html

Hope all goes well and let us know, I have thought about this type of conversion before.

Mike

[FEF]

I think I read the '94-'95 6.5L had a mechanical pump. That appears to be the easiest swap I see. At least the engine should be pretty easy to get.

The Cummins is an interesting idea. Honestly, I'd like to put one in, if they're not too long. It's hard to find info on engine costs, and dimensions. A pont in the right direction would be good, if it's nearly the same cost.

My tranny guy is VERY good. He's been been building odd-ball stuff for me, for nearly 10 years. He's a good guy to know, though not cheap.

This swap appears to be VERY possible, with no nasty surprizes.

It's the Cummins and the 6.5L that are on the scale. WHile the Cummins may be better, the 6.5L will likely be lighter. In this case (torsion bar suspension), I need to keep it as light as possible.

Tough decisions, indeed

[a5150nut]

I think I read the '94-'95 6.5L had a mechanical pump. That appears to be the easiest swap I see. At least the engine should be pretty easy to get.

The Cummins is an interesting idea. Honestly, I'd like to put one in, if they're not too long. It's hard to find info on engine costs, and dimensions. A pont in the right direction would be good, if it's nearly the same cost.

My tranny guy is VERY good. He's been been building odd-ball stuff for me, for nearly 10 years. He's a good guy to know, though not cheap.

This swap appears to be VERY possible, with no nasty surprizes.

It's the Cummins and the 6.5L that are on the scale. WHile the Cummins may be better, the 6.5L will likely be lighter. In this case (torsion bar suspension), I need to keep it as light as possible.

Tough decisions, indeed

93 is the last of the mechanical pumps. 94 starts the electronic units. You can put the mechanical on in place of the electronic pump.

[FEF]

Update:

The rear of the Cummins engines, where it mates to the bellhousing, goes down past the center of line of the crank. This is bad. What's worse is that the adapter will add a few inces to the total length from the rear of the bell housing to the timing cover area of the enging. This is a show stopper, becasue my engine mounts are not on the side, but on the front of the engine, and the rear of the tranny. The Cummins is ruled out.

I've found a Canadian (not that it matters much) '88 Suburban. It's actually in pretty darn good shape, and kinda a shame to pick its bones and sell the rest.

I'm getting it (will be getting it. It's not in my possession, yet) for a price where I could resell it, if I find the engine. I plan to drive it around a bit to get used to the Chevy diesel oddities. Then I'll pull the engine, and a bunch of other stuff, and put it in the Revcon (Toronado drivetrain).

It's slow going, but it's going.

[EWC]

Don't mean to kill your idea but I thought someone had posted here that the problem with the 6.2/6.5 with the TH425 was the rear exhaust manifold . Seems they had clearance issues or couldn't get a manifold to work with that trans . Hope I'm wrong .

[FEF]

I've been driving the Suburban as a daily driver. Anyone considering a conversion, I advise actually driving the donor vehicle for a while. In my case, I'm learning quite a bit about what's really required to make the engine run. I'm also learning quite a bit about things particular to the GM diesels. They're not bad, but they are quite a bit different from the OM352/OM366 I have experiance with.

With regard to the oil filter placement issue, I'm going under the assumption that the relocator will fit between the block and the TH425. I won't have that answer till I get a lot closet to pulling the engine. Yes, it's true that the LH ehanust might be trouble, but I've been playing with the idea of having the manifold reversed such that it's pointing up, and mounting a turbo on it. The junk yard turbo guys are still debating how it would go with the turbo being spun from one bank, then having the RH, and LH banks "Y" just to the rear of the engine. At the very least, custom headers will fix any exhaust routing issues.

What I'm looking for is a 3/4" to 1" indicator that I can put in the dash with "Glow Plug" on it. Lord knows I'm pretty good as cheasing together any number of things, but I'm trying to make this conversion as clean as possible. Do any of you know the make/model of a vahicle that might have a removable glow plug light that I can get from the bone yard?

[a5150nut]

Not a bad idea driving the donor vihicle. But many purchase wrecked vehicles and don't get the chance.

Are you talking about running the turbo off just one manifold? You will need both sides pushing the turbo to get the boost out off it.

Rat Shack for a panel light. Won't have the lettering on it, but would make a clean install.

Keep us informed on your progress.

[journeyman]

I have heard that the 6.2's when properly built are underrated.

That could make a good start for you and if you are not satisfied with the performance (power OR mpg's) you can have it rebuilt, knowing that the conversion work is already done.

What is your R&P ratio?
That could be a limiting factor on a 1:1 transmission like the TH.
What is available for the transverse TH?
Generally I say taller (lower numerically) is better, but in a motor home you will need a low gear for starting out.

Also, did your builder use the stock (2.48, 1.48, 1.00) gear ratios?

[FEF]

UPDATE:

I've been playing with the glow plug circuit on the donor vehicle. I've found that the temp sensor is normally open. When I put a jumper in, the glow circuit doesn't work. But we all knew that.

The next step is to bypass the temp relay that's controlled by the ECU. I think all I have to do is jump the two redish colored wires, and I'm done. I'd like to take that part of the wiring harness with the engine, so I'll track down where those wires originate, and make them truly bypass the ecu garbage.... In theory, of course.

I'm still working finding a wafer thin oil filter relocator. I havn't tried too hard to find one, but it's about that time.

No roadblocks, just more tinkering.

[FEF]

UPDATE:
I've been driving the 'Burb around. I've learned a lot. However, Friday, I ran into something I couldn't pass up... A '82 C-20 (pretty sure) "Camper Special" for $500.

I bought it. I didn't even dicker about the price, really. The truck looks like rolling dog poo, but you know... Electrical wires strug around like noodles (I really hate that). Mechanically, it's not in bad shape. He's got recepits for oil changes, and all the joints have grease gushing from the zerts, for example. It ran pretty darn well, with an estimated mileage of about 200K.

I'm hoping that it is the '82 block. That's the sweetest block (assuming it's not horrably cracked somewhere) for a motorhome that will tow, so I'm told. The down side is I've read the '82 injectors are different. That's bad, becasue a turbo will go on it one day.

For $500, I can pick the meat off it's bones, and throw the rest to the Wolfs. Or, maybe I'll put the Olds 455 in it and sell it for $500

Questions:
- If I find it is an '82 block, are the heads an issue?
- Should I consider swapping heads with the '88 Burb? That's a lot of work, but I'll do it, if it's "the right thing to do".
- It has no blow-by when cold, but still appears to have too much soot at the cold start. IP issue, perhaps?
- There's an odd sound heard when you take off the oil filler cap. It sounds kinda like it could be the PCV valve equilivent. Now that I think about it, maybe a loose timing chain? I don't think it's the chain, though. I've heard timing chains (on gassers) before.

I haven't forgotten about the pictures. I'm cleaning the shop this weekend so I'll have a place to lay-out the stuff.

[FEF]

Thought I'd catch everyone up on what's going on.

I found a 6.5L xx599 NA engine for a reasonable price. The compression is between 400-425 psi, and I can see hone marks on the cylinder walls. I did find one score a bit deaper then I'd like to see, but it wasn't too bad. This leads me to believe the engine does have the near 65,000 miles the PO claims it had. I can't think of any reason not to run it like it is.

The left bank exhaust will be an issue. I think I'm looking for Hummer manifolds, because they exit to the rear and not down.

I still need to modify the front engine mount. On these coaches, the engine mounts are in front and rear, not on the sides. It's not much trouble, it's just getting to it, and a bit of fab work.

I have the oil filter relocater, -8 AN hose for the engine and tranny oil lines, the BOP-GM adapter plate, and a few other tid-bits. I still have to drop the old 455 out the bottom, then I can start putting the front end back together.

I'm trying hard to get it road worthy by May 1st.

[FEF]

Here's some pics:

I have to find a filter relocater that's under 1-3/4". That may be tough. The one I got was perfect in height, but not big enough in diameter. The 6B filter is bigger then the SB filter.

I need to cut up my oil pan. It's likely to be easier then finding a shorter sump.

The front engine mount I made (pics later) covers the manual fuel pump. I'll try to find a different type, but as it is now, I may have to pull the pin out and use an electric pump. I'm thinking that I could put a 5psi oil pressure sensor. That should stop the pumping if something bad should happen.

I guess I'm cutting the oil pan, and looking for a thin relocator that's a larger diameter.

Any thoughts?

[FEF]

I've run into a show stopper. The diesel direct drive and gear driven starter hit the right half-shaft flange. The starters are about 1" too long.

It's too easy to miss something like this in conversion projects. I'm having to dig deep to find a solution. Basically, I have 3 options:

1} Rework the right axle shafts. - As it is now, the half shaft bolts to a flange on a shaft that goes under the oil pan (pics to come). While this is an option, it will take a long while to research what's required to find a shorter half shaft. Unless... I could have someone make me a longer axle shaft that goes under the oil pan, and have the stock half-shaft shortened. That's a pain, though. It means the CV joint will have to be rebuilt and not replaced. That's a drag.

2) Find a diesel starter that's 1" shorter. I have no idea where to start looking for that. There must be one out there somewhere.

3) Have a flex plate made that's the Olds diameter and tooth count but with the diesel bolt patterns and weighted for the 6.2/6.5. I suppose it could happen. It's just a matter of finding someone that would do it. However, after it's done, I'm not sure the Olds starter would turn it over.

This is a tough one. I could use an idea or two.

Thanks,

[JeepSJ]

Try Powermaster for the starter. They make a high-torque starter for the 6.2/6.5. I don't know if it is any smaller than stock, but it would not hurt to ask.

[DmaxMaverick]

The gear reduction starters are significantly smaller (and lighter!) than direct drives. You may get lucky, if it's small enough in the right place.

[convert2diesel]

Had the same problem with the Buick conversion, though with me it was the cross member. Easy fix...notched out the cross member.

Before that tho, I went through the same thought process. All of the 6.2/6.5 starters are the same length. They are made to use the factory front hanger. Even the geared starters are the same length, just smaller in diameter.

A local rebuild shop here said he could re-work a starter from a big block Chevy to produce the power but that would have cost a bunch. Not to mention you would have to do two and keep one for a spare. Not something that any old re-builder is willing to do.

You could also try your local speed shop. Seems a number of firms are making high torque starters for the high compression gassers.

Bill