Detroit 4-71 exhaust manifold temp question

[fishingbucks]

Have a newly rebuilt 4-71 2 valve Detroit that cranks and runs good. But, exhaust manifold not heating up evenly. Gets too hot to touch on cylinder 1 and 2 within a couple of minutes as expected BUT manifold on cylinder 3 and 4 doesn’t get hot at all. Can lay my hand on it and leave it there. I currently don’t have a thermostat in it. Could that be the reason? Also, injectors are newly rebuilt and purged of air so I don’t think it’s a firing issue. As I said, it cranks and runs good. I’m puzzled. Any thoughts?

 

[mitch504]

Get a cheap temp gun and measure actual temps

 

[Coaldust]

I think the rule of thumb is something like no more than 100F difference between holes.

 

[Vetech63]

Post a pic of your exhaust manifold. If it's an outlet type on the end, then your port temp will be different on the other end. Port 1 may be cooler when the dump out of the manifold is past #4.....the more ports you add as the exhaust gases run through the hotter the manifold will get, to a point. Once the engine reaches operating temp, the temp of the manifold should be relatively even across it. It will make a difference as to where you are shooting the temp too. Also, slight variation of the injector timing between the injectors and the rack adjustment will cause a cylinder to run hot.
Is there a reason the cylinder head wasn't converted to the 4-valve design?

 

[fishingbucks]

I have a temp gun. Didn’t run it long in case there was a problem. Plus, wanted to get thermostat put in before I ran it a while. Exhaust manifold is a vertical stack in the middle. As far as 2 vs 4 valve head, it was a 2 valve so that’s what we built.

 

[John C.]

Sounds more like the injectors were not set evenly.

I hadn't heard that you could change a 2 valve head to a 4 valve. All the 2 valve 71s I dealt with were low blocks.

 

[Vetech63]

We did some conversions way back in the day when I was still learning in the 80s. I wasn't lead back then so I don't remember all the details. I was thinking it was just changing over the valvetrain components.

 

[Vetech63]

Did you do the initial tuning adjustments according to a service manual? You can't just pull and install rebuilt injectors without retiming the injector heights and adjusting the fuel rack. Its very easy to have bad adjustments and over/ under fuel each cylinder individually

 

[Welder Dave]

The manifold looks like it has had some substantial welding done on it.

 

[terex herder]

And its still together. Somebody was a very good welder, as (especially old) exhaust manifolds are about the most difficult piece of cast iron one can try to weld. By the looks of it, somebody knocked the muffler off, and it was attached to the manifold way to good.

 

[John C.]

All the slobber below the stack is all too familiar.

 

[fishingbucks]

Yes we set injectors with tool and fuel rack per manual.

 

[fishingbucks]

Update: after running it yesterday for about 7 minutes the exhaust manifold on cylinder 3 and 4 did finally warm up but was 30 degrees cooler with temp gun than cylinders 1 and 2. Shooting the gun on head thought it was consistent on all 4 cylinders running 160 degrees. The engine cranks good and runs good so this is still very puzzling to me. My final observation is that half the exhaust manifold takes a lot longer to heat up than the other half and half runs a bit cooler. Should I be concerned about this?

 

[fishingbucks]

 

[kshansen]

Changing to a 4 valve head if a high block should have been as easy as just bolting one on, well I think you might want to replace the injectors and you would need the rockers and bridges from the 4 valve engine also.

We did just that many years ago when building up an engine to run a crusher. Sad to say that engine was only run for one or two seasons then parked. As of a year ago I know it was still sitting in the store room unused for maybe 20 years. It was fired up every few years and last time was a couple years back.

And yes I hope you can put that engine to work soon as that wet stacking is not good for it. Needs to be worked to seat rings. Not good to run any diesel at too little load but think Detroits are the worst.

 

[DMiller]

Only Designed oil leak ever constructed, DD.

 

[John C.]

I've just never seen a two valve head installed on a high block engine. I guess you learn all kinds of stuff here.

 

[kshansen]

I've just never seen a two valve head installed on a high block engine. I guess you learn all kinds of stuff here.

Forget the model but the one we converted to 4-valve was out of an old Northwest crane. We had scrapped the crane a few years before but saved the engine just incase. It worked out good for this application as it came with it's own radiator and nice Rockford flywheel clutch. When rebuilding it we converted to a modern alternator and installed a factory emergency shut down system as we knew this unit would be running unattended 99% of the time.

 

[kshansen]

Only Designed oil leak ever constructed, DD.

Actually if properly built and used in the right application I saw more than a few that did not seem to have that problem. The newer water below ports were better as they did not have the troublesome air box covers with the cork gaskets that dried out and shrank making a mess.

One of the worst things I ever saw was putting them in an application where they were not worked hard enough. Like the little 3-53 Detroit genset we had. They decided to put it in a trailer with a 3412 genset. The only thing that 3-53 did was to run nights and weekends powering the block heaters on the 3412 and a couple security lights. Probably could have used a little one cylinder Honda genset for that! That 3-53 hardly knew anything was hooked to it!

 

[Welder Dave]

Talking about generators, I've been wondering if anyone has used a diesel generator to power a shop? I don't have power at my property and it would likely cost over 50K to get it hooked up. I was thinking of getting about a 20kw generator so I could run 220 equipment like an air compressor or Mig welder. I don't live at the property so it would be run intermittently. Would this be a cost effective way to have heavier power when I need it?