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GM - Chevy 250 Engine Conversion

177287 Views 782 Replies 86 Participants Last post by  Steyn
Starting a separate thread on the 230 & 250 inline 6-cylinder engine conversions.
This engine conversion will bolt in and out of a 90/119/130 without vehicle modifications, like the 292 making it an easy, inexpensive weekend conversion.
Since the 230 and 250 blocks are 2" shorter than the 292, and the ancillary mounts are different, this thread should eliminate any confusion with the 292.

Why convert?
The performance and ease of conversion are remarkable and well-suited to a Defender-style vehicle.
After driving small diesel for over 15 years and having to deal with high maintenance and poor performance coupled with reliability issues it was time for something better.
We built conversions for the Diahatsu 2.8 TD, the Iveco 2.8 and 3.1 TDI, and the OM617, and drove Land Rovers with 200 and 300 TDI engines.
These mechanical diesel are generally loud and smoky while the GM inline 6 is smooth and so quiet, you often don't hear it idling or driving.

The Chevy 250 was used in cars, trucks, and vans, and had many industrial uses being manufactured from 1962 to 1990.
A good used GM inline 6-cylinder engine typically sells for under $500 and is usually less than $250.
The cam is driven by metal timing gears eliminating the need to change a timing belt or timing chain.
The GM High Energy Ignition (HEI) systems are extremely reliable and were used on military vehicles without issue when submerged.
Parts are inexpensive with over-the-counter support from any local parts store.

There were several different versions of the 250 engine with different cylinder heads.
Some of the heads had a separate bolt-on manifold, while other versions had the inlet manifold integrated into the head casting.
Both versions will fit into a 90/110/130 using our conversion kit.

If you want Electronic Fuel Injection (EFI), the Holley Sniper is a good choice.
We will be working out the details for the Sniper as we did for the 292 conversions.

The other deciding factor was the accessibility to the engine and all the components.
Everything is within easy reach making for much shorter work intervals.
I timed changing a starter with hand tools which took 12 minutes.

With HEI and EFI, the only maintenance is changing the oil along with the rare wires, plugs, cap, rotor, and air filter renewals.

We will be offering kits as soon as they are manufactured.
As of the date of this post, we are waiting on the engine adapter castings to be machined, which hopefully won't take much longer.
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Buying Chevrolet parts when you're more accustomed to the genteel world of British and Swedish cars can sometimes be a bit of culture shock. Witness this message exchange when someone I know responded to a Kijiji ad for a Chev inline 6 with attached SM465 for $200:

"Two quick questions: Is it a 250 or a 292? Are the manifolds bolt-on, or cast in the head? "

"I don’t know I’m old town Tarzan motor Inn importantly"

I advised him to engage an interpreter.
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Good day Mr. Davis, I have and old NADA with one of your early conversions I believe. It suffered from a very shoddy radiator and throttle linkage installation which I'm in the process of correcting. Can you tell me which radiator and hoses to order and what you did for the throttle linkage? All the cross flow radiators I've found are too wide and there is no telling what this radiator is from.

Thanks!
If you have an NADA 90 with a 250 post up pictures here.

If you have an earlier NADA series read below, if not ignore.
Here is a link to one of the 4 cylinder engines I built, below.
They are designed to bolt to the original transmission and frame motor mounts and they use the stock radiator that the vehicle left the factory with.
There were others that built a few 4 cylinder GM engines that were installed in series Land Rovers and people assume these engines came from me.
If you get some pictures, post them up in your own thread separate from this one and we'll see if I can help.
My conversions for the series came with accelerator linkage that bolted in and worked fine so this engine may not have come from me.
That doesn't mean the PO installed the linkage properly or that the engine didn't come from me.
Without pictures, it will be impossible to determine if it was an engine I supplied.
.
GM 3.0 Liter in a Santana Series III
Good day Mr. Davis, I have and old NADA with one of your early conversions I believe. It suffered from a very shoddy radiator and throttle linkage installation which I'm in the process of correcting. Can you tell me which radiator and hoses to order and what you did for the throttle linkage? All the cross flow radiators I've found are too wide and there is no telling what this radiator is from.

Thanks!
Give us a heads-up when you open a new thread to pursue this. We're all interested in these swaps.
Curious if anyone hears anything specific in this engine when it's near idle. It seems to gasp and then catch up. I'm not sure what's up. (Timing good -- ranging from 15 advanced to 0, most vaccum plugged, still playing with mixture screw)



After trying the original Rochester, a Holley 4bbl, a new Rochester, I quit listening to people and ordered a Weber 32/36 carb and adapter. It's starting to run now. Still not sure if it's a good engine or not. Will need to play with different mixtures and advances but it's getting close. If anyone can listen to that and has any ideas, let me know.

(Know that I've tried timing any where from 15 degrees advanced to perfectly 0 degrees. ~10 degrees advanced seems to be best so far. It starts to almost backfire at zero degrees.)
You need to install a fuel shutoff needle and seat valve with a viton tipped needle, otherwise the fuel will overflow in the DGV Weber carb.
You need to install a fuel shutoff needle and seat valve with a viton tipped needle, otherwise the fuel will overflow in the DGV Weber carb.
Did you by chance see the fuel regulator and gauge showing 2lbs of fuel pressure?
Yes sir.
No idea why, but the brass needles work halfway.
I have been through hours upon hours of using everything except a viton tipped needle and wasted time with everything else.
Yes sir.
No idea why, but the brass needles work halfway.
I have been through hours upon hours of using everything except a viton tipped needle and wasted time with everything else.
K. I have concluded this is never ending. I’m done tinkering and trying. Scrapping the build.

I’m thousands ($4000?) into this conversion that was supposed to be simple. I’m on the fourth carb. I had a running Escalade ready to go.
No one can just name a part or two that works. There is always some other thing to buy to make it work. It never ends and never runs. I have to stop some time. I do not believe that valve will make a difference.
Matt, the content of post 769 is based on my experience with running the weber 2 barrel on GM 4 cylinder engines.
Here is a 3.0 GM 4 cylinder with a Weber 38 with the viton tipped needle in the fuel shutoff valve fed by the stock fuel pump.
The engine shown has no exhaust and was being run for the first time in a Series III Santana 109.


Your engine could run this well provided it is a good engine to begin with.
Throwing the towel in at this juncture is perhaps not the best choice, but only you can decide what is best for you.
.
Matt, the content of post 769 is based on my experience with running the weber 2 barrel on GM 4 cylinder engines.
Here is a 3.0 GM 4 cylinder with a Weber 38 with the viton tipped needle in the fuel shutoff valve fed by the stock fuel pump.
The engine shown has no exhaust and was being run for the first time in a Series III Santana 109.

Robert, here are forums discussing the 250 with the same Weber carb: Anybody running a 32/36 Weber on a 250? - The 1947 - Present Chevrolet & GMC Truck Message Board Network
They don’t mention the valve. I don’t want to rebuild carbs or custom modify them. The time for that was two years ago. If this is really that simple, it would be running. How many carbs should I try? 5? 6?
If I do exactly as you say, can you tell me what I might expect to happen?

Why do I have to keep spending money just to have people tell me to do something different? What will it be after I tear up this carb I just bought? “Should not have bought integrated head”?
I need an end to this. I can admit defeat. I lost.
It would be insane for me to keep listening and expect something different.
You signed off on the Holley 4bbl a year ago. We discussed mounting plates. Here we are now. I don’t have confidence this will end with a running truck.
Matt:
If there are forums discussing the 250 with the same Weber carb: Anybody running a 32/36 Weber on a 250? - The 1947 - Present Chevrolet & GMC Truck Message Board Network That's OK by me.
I am just trying to help you by sharing my experience with the carb you chose.

I realize you are at the end of your tether.
When you seek advice, you'll get responses by people genuinely willing to help you.
Like all opinions, experienced and less experienced, good and bad, there will be all kinds and you have to filter through.
Best wishes and hope you are successful before you disengage.
My 250 has been going for over 4 years and driven daily.
The only maintenance has been oil and filter changes.
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For our Canadian members:




For our American members, that $183 US.
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I would literally tow the truck to some or ANY reasonable mechanic I’m my area. Not a technician but a real mechanic, (if DC metro area has tons of them so does your town)

pay them 2 hours to tune the motor for you. Will cost you no more than 150 an hour.

No offense but I don’t think you know how to tune it. Throwing money at a motor and not knowing how to use the tools at hand is like throwing money at a stripper thinking you are courting a wife.
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Throwing money at a motor and not knowing how to use the tools at hand is like throwing money at a stripper thinking you are courting a wife.
Well jeez, she's worked out pretty well so far....

😁
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Curious if anyone hears anything specific in this engine when it's near idle. It seems to gasp and then catch up. I'm not sure what's up. (Timing good -- ranging from 15 advanced to 0, most vaccum plugged, still playing with mixture screw)



After trying the original Rochester, a Holley 4bbl, a new Rochester, I quit listening to people and ordered a Weber 32/36 carb and adapter. It's starting to run now. Still not sure if it's a good engine or not. Will need to play with different mixtures and advances but it's getting close. If anyone can listen to that and has any ideas, let me know.

(Know that I've tried timing any where from 15 degrees advanced to perfectly 0 degrees. ~10 degrees advanced seems to be best so far. It starts to almost backfire at zero degrees.)
I will give it a try and help you out if you are interested, I am not a mechanic or technician but I have spent more than my fair share of hours and dollars building vehicles.
Questions/comments
1. We need to establish a standard baseline from which to start.
2. Plug ALL vacuum ports on the carb and engine!! Nothing should be open to the atmosphere!
3. Reset the A/F screws on the carb back to stock which is probably 1.5 to 2 turns out
4. Does it run any differently? We need to establish a steady idle so we can tune from there, if it won't idle then no sense in trying to tune.
5. Buy a can of starting fluid and sparingly spray around the base of the carburetor checking for vacuum leaks, I am starting to believe you have a vacuum leak either in an open port, carb base, or intake. If there is a leak then the idle will increase.
6. Do you have a vacuum gauge?
7. Do you have a way to do a compression check?
8. If fuel pressure is so low why do you have a fuel regulator? Consider bypassing it.
9. Remove fuel regulator and see what the pressure is, needs to be higher than it currently is. Bad fuel pump, clogged fuel line, worn cam eccentric
10. If you can't get fuel pressure up consider buying the cheapest electric fuel pump you can, probably $30.00, and run it from a gas can to rule out line and fuel tank problems. This is only a temporary setup just for testing and diagnosing.
11. It appears that the engine is really running off the accelerator pump squirts and not fuel being sucked in from the fuel bowl/s. Maybe not enough fuel or maybe the float bowl is not filling for some reason, incorrectly adjusted, stuck float, who knows but we need to start from scratch.
Hard to diagnose based off a short video but that is where I would start.
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K. I have concluded this is never ending. I’m done tinkering and trying. Scrapping the build.

I’m thousands ($4000?) into this conversion that was supposed to be simple. I’m on the fourth carb. I had a running Escalade ready to go.
No one can just name a part or two that works. There is always some other thing to buy to make it work. It never ends and never runs. I have to stop some time. I do not believe that valve will make a difference.
Hey I was just reading through your troubles and the advice above is perfect to get you diagnosed. Also looking at your pic it may just be a shadow or casting mark but it looks like your intake has a crack in it. You may also want to smoke test your intake to see if you are sealed up. it would account for your symptoms. Realistically you can pretty much get it running on any carb if everything else is good.
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I am leaning towards vacuum leak or cracked/not sealed intake manifold, I had two that were cracked.
FYI he is running an integrated head smog motor.
My hunch is that it is full of vacuum leaks.
Base idle shoul be around 8 DBTDC.

not sure if the fuel tank was flushed of old diesel and sludge as recommended as it wasn’t at last conversation.

previous discussion wasthat an electric fuel pump was used, advised to switch to a $30 mechanical pump on theblock.

not sure if firing order is ok?

with HEI gap plugs to 40

buy inexpensive vacuum gauge plug to manifold vacuum and tune the carb. Without that it is impossible.
This video is great
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