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GM 3-71 Injectors


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  #1  
Old 11-11-2018, 11:34:31 AM
glennh glennh is offline
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Default GM 3-71 Injectors

Hello All.

I am new on this board, but I have been fascinated with making old things run for a long time, and I have found a lot of useful information here.

My question is about a new engine that I acquired this week. It is a 3-71 GM diesel that is (hopefully) destined to power my dad's Belsaw sawmill.

The 3-71 was removed from a crane about 5 years ago, and is set up on a home made frame with a Twindisc PTO. The engine itself has a thick layer of yellow paint on top, with orange underneath, and a spot of Olive Drab in places. Based on the paint and the intake/exhaust setup, I have decided that it is most likely from an Allis Chalmers HD7.

My question though, is about the injectors. Everything about the engine appears to be ready to run after a good flushing and cleaning, except the injectors. All three are stuck.

I have removed the injectors and let them soak in diesel for a few days. A gentle tapping on the plunger didn't do them any good, so I opened one up. Repeated soaking, spraying and tapping has failed to loosen the plunger on the one I took apart, so I have decided to look for new (rebuilt) injectors. The problem is finding the right ones. The injectors have no letter, only "GM Diesel Equipment 70" The in/out ports are not offset as on other Detroits I have worked on.

Can anyone direct me to a good reference for old GM injectors so that I can cross these injectors to something more recent?

Thanks for any help.

Glenn
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  #2  
Old 11-11-2018, 11:53:58 AM
Norm W Norm W is online now
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Default Re: GM 3-71 injectors

It sounds as though you have a HV70 injector. If you wanted to you could replace them with HN60 injectors. You probably have a two valve head, which takes the old High Valve injector body. The "N" type has a better spray pattern hence the H (high valve body) N (N type spray pattern) label.
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Old 11-11-2018, 01:47:06 PM
K-Tron K-Tron is offline
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Default Re: GM 3-71 injectors

If the only number on the injector is 70, the engine you are working on is very old. The 60, 70, 80 and 90 injectors were 1937-~1946. Your engine will run much better with a HV (High Valve) type injector. HV7 would be the equivalent of the old GM 70. The HV injectors have the same body as the old number series GM injectors. You will not be able to run offset body (current) injectors in your engine. I may be interested in your old original injectors if you want to part with them.

Chris
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Old 11-11-2018, 01:54:18 PM
glennh glennh is offline
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Default Re: GM 3-71 injectors

Thanks Norm. I have read about the HN injector elsewhere. My biggest concern is the orientation of the fuel ports. I have found photos of HV injectors that have the offset ports. How can I be sure that I'm getting something that will work? Pictures make everything easier so here they are.
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Old 11-11-2018, 01:58:20 PM
glennh glennh is offline
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Default

Name:  hv7.jpg
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Size:  1.4 KBThis is a photo from Ebay. Hope it's big enough to see. This appears to be an HV7 with the offset body.

Chris,

The Allis HD7 used the 3-71 in the 1940s, so that would match my suspicions.

This photo is better.
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  #6  
Old 11-12-2018, 02:26:31 AM
The Diesel Doctor The Diesel Doctor is offline
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Default Re: GM 3-71 injectors

Quote:
Originally Posted by glennh View Post
Hello All.

I am new on this board, but I have been fascinated with making old things run for a long time, and I have found a lot of useful information here.

My question is about a new engine that I acquired this week. It is a 3-71 GM diesel that is (hopefully) destined to power my dad's Belsaw sawmill.

The 3-71 was removed from a crane about 5 years ago, and is set up on a home made frame with a Twindisc PTO. The engine itself has a thick layer of yellow paint on top, with orange underneath, and a spot of Olive Drab in places. Based on the paint and the intake/exhaust setup, I have decided that it is most likely from an Allis Chalmers HD7.

My question though, is about the injectors. Everything about the engine appears to be ready to run after a good flushing and cleaning, except the injectors. All three are stuck.

I have removed the injectors and let them soak in diesel for a few days. A gentle tapping on the plunger didn't do them any good, so I opened one up. Repeated soaking, spraying and tapping has failed to loosen the plunger on the one I took apart, so I have decided to look for new (rebuilt) injectors. The problem is finding the right ones. The injectors have no letter, only "GM Diesel Equipment 70" The in/out ports are not offset as on other Detroits I have worked on.

Can anyone direct me to a good reference for old GM injectors so that I can cross these injectors to something more recent?

Thanks for any help.

Glenn
You can get a better price if you have a acceptable core when you buy a rebuilt injector. soak your injector in WD40 for a few days and then tap the control rack back in forth with a small hammer. If it has an undamaged tip and a free rack its a good core. I get my injectors from PC Industries in Afton Wyoming. AL
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Old 11-12-2018, 09:40:45 AM
miltruck miltruck is offline
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Default Re: GM 3-71 injectors

I agree with all of the above, but would recommend that you down size the injectors to the smallest ones suitable for the 3-71. Not sure which Bel-Saw mill you have, but my father sawed hundreds of logs with a 42/48" mill using a Long 460 tractor to power the saw via a pto setup. Tractor is only 45 pto hp and would saw 20" white pine like it was balsa wood. Red oak was a little tougher but still worked fine if you adjusted the feed rate.

Again, not knowing what setup you have, you may have to come up with a step down pulley system as my father's mill ran at about 550-650 rpm and clockwise when viewed from the rear end of the tractor. The Detroit won't like to run under load below 1,200 rpm under load but may work using a 2:1 step down.
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Old 11-12-2018, 11:00:38 AM
glennh glennh is offline
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Default Re: GM 3-71 injectors

Belsaw advertised that the mill could be run with a 30 HP engine and the power feedworks takes another 25HP.

We have converted to a larger mandrel and a hydraulic drive for the feedworks, so we're losing some power there. We also have to run it through a belt reduction as you said, so that eats up some power. It's currently under power with a chevy 250 gas engine running through an SM465 4 speed running in reverse. This powers a main shaft that runs the hydraulic pump and belt drives to the mandrel. This unit runs well and is quiet, but we can't get a governor to keep up with the mill.

Given all of the advice above, I think that I want to go with the HN60 injectors, but I'm still not clear on the High Valve designation. As long as the fuel ports are straight across and not offset, the injector should work?

Thanks for all of the help. This is a great forum.
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Old 11-12-2018, 11:58:14 AM
Norm W Norm W is online now
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Default Re: GM 3-71 injectors

The offset fuel ports are for the 4valve heads. You have an engine with a 2valve head. That takes the type with the side by side ports. The 71 series engines put out about 35hp per cylinder at full power. The smaller injectors will produce less power, but run cleaner, because there will be more "Air" to fuel when running. "Rolling Coal" just wastes fuel. I dropped from HV70 to HN55 and eliminated all the smoke on acceleration in my 671. It dropped the HP from 238 to about 185, but the mileage went from 6.5 to 10.5. I can still cruse at 65mph.
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Old 11-12-2018, 12:29:37 PM
K-Tron K-Tron is offline
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Default Re: GM 3-71 injectors

If you cannot find new or rebuilt injectors, a good 2 cycle Detroit diesel shop can put the innards of an offset body "N" injector into your 70 straight body injectors. I know several folks that have done so. It looks original under the valve cover and runs without the constant gray/black haze the original 70 injectors had while running. I doubt any shop will give you any money for those old injector cores, they are not serviceable anymore. Leid Diesel in PA likely has a matching set of rebuilt straight body injectors on the shelf for you. They would love to hear about your old diesel & your project.

Chris
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