trying to get the 251 running again?

[citizensoldier]

Ok guys here is the deal. I have put a new intake and exhaust manifold, new carburator, new distributor with electric ignition, re-built fuel pump, new exhaust, new plugs, new wiring harness, and new others.
I have been trying to get it started and found out I had no spark. I then replaced the coil and now have good spark.
It started up and ran for about 40 seconds and then stalled. I have tapped the new carb a few times too. At first I thought I was not getting fuel. WRONG I pulled the fuel line and the pump is pumping??? I tryed a bit of starting fluid and nothing. Checked spark again and got good spark??
Any suggestions? This motor ran good before all this it just had a cracked exhaust manifold.. Its got me baffled. I have re checked the distributor timing to make sure I had it at top dead center of #1 and it is right. Also it started and ran and when it ran it sounded good...
HELP!~

 

[Jones]

Vacuum leak? Spray intake and carb gasket seams with WD40 or other spray oil and see what you get. The oil will be thick enough to temporarily close up any leaks. Spraying when running will often pinpoint a leak by a change in RPM.
If it flooded out for whatever reason then pulling the plugs and drying the electrode ends out with a propane torch will often get things going again. The heat drys and the open flame burns off any residual gas. Of course, don't do this procedure around any fuel sources like the carb, fuel pump, etc.

 

[ida34]

How did you check for spark? Did you pull the wire off and check it with a checker or did you use an inductive checker with the wire still connected to the spark plug? Just because you get spark from the plug wire does not mean the plugs are sparking. The plugs may be fouled. The gap may be jumped. Did you pull them out and check them? Try checking the plugs.

 

[citizensoldier]

plugs

I pulled the plug and turned it over. I had a nice blue spark. These are also new plugs but I will re-check the gap to make sure. That electric ignitor puts out some good clean spark. No more points.
I drained the battery so I am charging them now and will try some of the mentioned things tomarrow.

 

[Jones]

Bear with me on this one; can't remember right now if Unimogs have accelerator pumps or not. With the engine shut down and air cleaner horn off you should be able to see down the carb throat and see if you get fuel spray when you work the throttle linkage. Fuel to the carb float bowl is not going to do any good if it can't get past a plugged jet. Do this check ONLY with the engine off. Past experience has taught me how flammable mustaches are in cases of an ill-timed back-fire. (The smell of burning mustache was bad enough but it was my buddy beating out the flames that put me in the E.R.)

 

[ida34]

Most Accelerator pumps have their own jets separate from the primary jets. It will tell you if the carb is getting fuel though. Remember, you need three things for an engine to run. Spark, compression, and fuel. If you have spark and the carb is giving fuel to the engine then it has to be compression. Pour a small amount of fuel down the carb then replace the aircleaner. This part is real important. Hold the throttle all the way open and try to start it. If it fires then check the carb. Something might have came loose that is clogging the intake ports to the primary jets. If it does not start or at least sputter like it is starting then I would check compression. If the compression is good then recheck timing. It has to be one of the items mentioned above. I would start over and check everything since it is obviously something elusive.

 

[m35a2cowner]

Won't Start

Make sure the distributer is set for top dead center on the compression stroke (both valves closed) Next make sure the spark continues the whole time the engine is cranking (loose wire) Check the firing order of the plug wires. Make sure when distributer is at top dead center on the compression stroke the rotor button is at the terminal of the first cylinder in the firing order. Check for cracks in the distributor cap. You might check all the other plugs to make sure they are not wet/flooded. If so, heat up with heat gun or torch to dry. Make sure what is going into carb is actually gasoline. Water might have gotten in tank, you never know.

 

[citizensoldier]

Found stuck valve?

Ok gods of all things OD.. Here is the situation on the 251 Canadian. Still would not run, had a friend over that has 5 M37's that all run and knows a little bit about them. We ran through all the normal checks. Good spark, got fuel,timing set right,plug wires right,and so on. Decided it may be the vaccum thing Charles at M-series rebuild mentioned to me awhil back. I had to just forget about the truck for a bit out of frustration,anyway compression check = #1 45lbs, #2-43 lbs, #3-NOTHING?? #4- 45lb's, #5-45lb's,and #6 54 lb's.
Exhaust valve on #3 is stuck! Whats the best way to un-stick it? I took a piece of hardwood and tapped very gently and nothing. Is there a good product that I can put down the cylinder to eat away bad gas residue? Do I have to pull the head? Next step please?
Could this be the reason it will not run again? Not enough vacuum for fuel adimizing? Uhhh...It seems like it would fire if even just run like pooooo... How are these compression readings? Are they to low?

 

[Desert Rat]

The stuck valve will cause the engine to not run. Kroil is THE way to get it unstuck. Get some and be patient in how it works. It's slow but effective. Trying to run the truck with a stuck valve is only begging for disaster.

 

[m35a2cowner]

stuck valve

DR is right penetrating oil will work its magic over time. Many moons ago we use to use something called Berryman's Chemtool to clean the varnish off of parts and valves and guides. I don't know if they are still in business. If for some reason the penetrating oil does not do the job you also try grabbing the spring retainer and move it back and forth while spraying more oil. I am guessing this is a flat head engine, you might also try very gently prying down on the retainer with one of those curved pry bars. Don't pry to hard you run the risk of bending the valve. If this is an overhead valve engine there are a couple of other things you might be able to do.

 

[m108]

RE: stuck valve

I know from experence a 230 will run with 1 or more valves stuck and the 251 is just a bigger version. I have poured Marvel Mystery oil in them to the point of almost flooding them out when running to un stick them on several engines.On a flat head a stuck valve can't hit any thing and damage it .If it was stuck shut it could possibly damage cam, tappet or valve right off the bat but I haven't seen it on several that have been brought back from the dead.I haven't ever checked the compression on a cold one but they all seem kind of low.I'll try to check mine tomorrow afternoon and let you know.How old is the gas in the tank?

 

[m108]

RE: stuck valve

I checked the compression on one of my 230's cold this afternoon and got between 95 and 105 psi on all cylinders. Are you sure your gauge is good ? It should run with 1 stuck valve.If it's firing even if the distributor is out of time it should pop,spit,cough or something if it's getting fuel. Pull the drain plug in the side of the carb and see if gas runs out.Do you have the air cleaner and elbow on it? Mice could have built nest in them while you had it apart and have the air shut off.

 

[citizensoldier]

Here is info from G741 site.

>Ok gods of all things OD.. Here is the situation on the
>251 Canadian. Still would not run, had a friend over that
>has 5 M37's that all run and knows a little bit about them.
>We ran through all the normal checks. Good spark, got
>fuel,timing set right,plug wires right,and so on. Decided it
>may be the vaccum thing Charles mentioned awhile back. I had
>to just forget about the truck for a bit out of
>frustration,anyway #1 45lbs, #2-43 lbs, #3-NOTHING?? #4-
>45lb's, #5-45lb's,and #6 54 lb's.
>Exhaust valve on #3 is stuck! Whats the best way to un-stick
>it? I took a piece of hardwood and tapped very gently and
>nothing. Is there a good product that I can put down the
>cylinder to eat away bad gas residue? Do I have to pull the
>head? Next step please?
>Could this be the reason it will not run again? Not enough
>vacuum for fuel adimizing? Uhhh...It seems like it would
>fire if even just run like pooooo... How are these
>compression readings? Are they to low?
>
You need not expect it to run with low readings like this. The stuck valve is the least of your problems. To run good, you'll need at least 100+ PSI at every cylinder. Less than 90 probably won't run at all or will be skipping & very rough. You need to investigate further to see what the deal is that is causing low readings. Pour a tablespoon or so of oil in the plug hole & re-test each cylinder (pouring in the oil 1 hole at a time just prior to testing each cylinder.) If you get a significantly higher PSI reading after the oil is induced, that would indicate that bad piston ring seal is the cause of the low readings. If you get little or no change in the reading after pouring in the oil, that would indicate the problem is the valves. Since you've established that 1 valve is stuck, you may have others that are partially stuck causing these low readings. Once you get the result of the 2nd test, you will then need to follow the indicators you get in order to correct the problems. If it's rings, you are facing a complete overhaul, if the indicators point toward valves, you may as well do a complete valve job. You are most definitely faced with 1 or the other based on the information you have given.

www.mseriesrebuild.com
Charles Talbert




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citizensoldier
unregistered user
01-Jul-06, 09:09 PM (pst)

2. "RE: Compression readings extremely low"
In response to message #1

Hey Charles! Your up late.. I was hoping to get a response from you. I will perform the test you mentioned tomarrow. It doesnt look good does it? Do you still have that 251 Canadian military block? At one time you said you had one laying around the shop. I was looking for a manifold set at the time but they were gone. How much to rebuild it and ship a "short block" to Michigan?
Hardened valve seats, boil and bore, check crank, new cam, pistons,rings,head milled,new valves and so on..The works.. for the block anyway?



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MSeriesRebuild
Member since 3-Aug-04
1461 posts 01-Jul-06, 09:26 PM (pst)

3. "RE: Sorry, no 251 at this time"
In response to message #2

Don't have anything to offer right now except 230's. For us to go through yours like you described, I'd say $2,000-$2,500 range, depending on how bad it may be or if any major parts were not usable & had to be replaced.
www.mseriesrebuild.com
Charles Talbert




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citizensoldier
unregistered user
01-Jul-06, 09:40 PM (pst)

4. "RE: Sorry, no 251 at this time"
In response to message #3

Any idea on freight? Thanks for the reply... You have been a great help and I appreciate it very much.



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MSeriesRebuild
Member since 3-Aug-04
1461 posts 02-Jul-06, 10:02 AM (pst)

7. "RE: Sorry, no 251 at this time"
In response to message #4

>Any idea on freight? Thanks for the reply... You have been a
>great help and I appreciate it very much.
Freight rates have taken a giant leap as you might expect with fuel cost increases. You would have to call your local motor freight co. for a quote since you would be the shipper.

www.mseriesrebuild.com
Charles Talbert




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citizensoldier
unregistered user
02-Jul-06, 08:46 AM (pst)

5. "RE: Compression readings extremely low"
In response to message #1

Second test #1=70 Psi, #2=65 Psi, #3=0 Psi, #4=70 Psi, #5=65 Psi, #6=55 Psi.
What do you think? Is this little difference bad valves or am I in for the big one?




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MSeriesRebuild
Member since 3-Aug-04
1461 posts 02-Jul-06, 09:58 AM (pst)

6. "RE: Compression readings extremely low"
In response to message #5

>Second test #1=70 Psi, #2=65 Psi, #3=0 Psi, #4=70 Psi, #5=65
>Psi, #6=55 Psi.
>What do you think? Is this little difference bad valves or
>am I in for the big one?
>
Leaking rings will usually be sealed by the oil which generally makes for significantly higher readings. Based on this information, I would further investigate for valve issues 1st. If the engine has been run even for a few minutes on stale gasoline, that is enough to do the valves in, what you are describing sounds like an all too familiar story. I say again, I could never make a solid diagnosis unless I could check it myself, sure sounds like valves to me though.

www.mseriesrebuild.com
Charles Talbert




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citizensoldier
unregistered user
02-Jul-06, 10:12 AM (pst)

8. "RE: Compression readings extremely low"
In response to message #6

Thats what I was thinking but I was unclear on "siginifant difference"? Well it wouldnt hurt to pull the head and do a valve job on it. If it turns out to be the rings then I will yank her out and have it rebuilt.
I bought this truck out of Canada and put fresh gas in it and ran it for a little bit before changing the manifolds. It did have bad gas in it though because the tank was a mess. I just had it Re-newed but it was too late... Oh well I learned the hard way on this on...



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Lifer
Member since 4-Aug-04
1140 posts 02-Jul-06, 11:26 AM (pst)

9. "RE: Compression readings extremely low"
In response to message #8

"Lessons learned the hard way are lessons best remembered," they say. At least you aren't pouring money down a hole by looking for the "quick and cheap" fix that doesn't exist. Go ahead and do whatever mechanical work is required and enjoy yourself doing it. Then, let the wife worry about the expense. After all...that's her job!



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powool
Member since 9-Aug-04
95 posts 03-Jul-06, 04:14 PM (pst)

10. "RE: Compression readings extremely low"
In response to message #8

I'm very interested in hearing your experience in valve tweaking - I'd like to see if my 230 can be brought back to life (even if just a summer) by some modest valve work (as opposed to an engine swap or full engine teardown).

Paul Anderson



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doodlebug
Member since 15-Jun-06
37 posts 03-Jul-06, 04:17 PM (pst)

11. "RE: Compression readings extremely low"
In response to message #6

Just curious. I'm not all that familiar with the flat head sixes, but does the engine have to be pulled to do a valve job, or can it be done in the vehicle?
Ron
1962 M37B1



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dr9487
Member since 1-Aug-04
901 posts 03-Jul-06, 05:02 PM (pst)

12. "RE: Compression readings extremely low"
In response to message #11

It can be done in the vehicle. You can take the valves to be done, but you need the correct tool to resurface the seats in the block. if they`re in good shape, you may be able to lap them in with valve grinding compound.
Rick



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citizensoldier
unregistered user
03-Jul-06, 05:51 PM (pst)

13. "RE: Compression readings extremely low"
In response to message #12

Well I am just going to dust off the manual and give her a go. I do have the correct tools for the seats. A complete set came with one of my buddies parts purchases. What I dont have is the special valve spring compressor. I guess I have to pull that damn manifold set off again! This will make the third time.
Any of you guys have a valve spring tool you will loan me? I will pay shipping both ways..
Also if any of you pro's want to share some secretes on doing this feel free to have at it! This is new territory for this shade tree mechanic.
Can the valve seats be changed with the engine in the truck? I wonder if I should have harnened seats put in if that is possible? If not it should last for a little bit shouldnt it? There is alway lead additive I guess..



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dr9487
Member since 1-Aug-04
901 posts 03-Jul-06, 06:29 PM (pst)

14. "RE: Compression readings extremely low"
In response to message #13

When you pull the head, look at the valves good. Spray penetrating oil around the guides and roll the engine. Make a note of any that don't close all the way. Tap them lightly as you turn the engine to get them working all the way. If they free up easy, you might get by with just a new head gasket. TRY THIS BEFORE YOU PULL THE MANIFOLDS!
Either way, you need to get them working so you can pull them out of the guides to take the valves out. I've had good success doing this on vehicles with stuck valves over the years. Good luck.
Rick



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brianacarey
unregistered user
03-Jul-06, 08:08 PM (pst)

15. "RE: Compression readings extremely low"
In response to message #13

Lane,
I might have a valve spring tool that will work. It is a big U shaped thing. I will send it if you want it, but I don't think they are that expensive. I bought mine at Sears for about 30 if I remember right. It might not be the best tool as I know some people have a lot better ones, but it worked for me. I have not used it on an M37. Let me know.
Jason




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Lifer
Member since 4-Aug-04
1140 posts 03-Jul-06, 08:25 PM (pst)

17. "RE: Compression readings extremely low"
In response to message #15

The "big U-shaped things" are for OHV engines with the valves in the heads. It has to go around the head to apply pressure to the springs. For flatheads, you need the "pliers" type.



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dr9487
Member since 1-Aug-04
901 posts 04-Jul-06, 05:20 AM (pst)

19. "RE: Compression readings extremely low"
In response to message #17

With the manifolds off, the U shaped one should work on a flathead as well. It may work better because it would give more room around the keeper area.
Rick



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Lifer
Member since 4-Aug-04
1140 posts 04-Jul-06, 06:20 AM (pst)

20. "RE: Compression readings extremely low"
In response to message #19

You have a point, there! Those "pliers" type spring compressors are a real pain to work with - even with the engine out of the vehicle where everything is "easy" to get to.



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BILL L
Member since 2-Aug-04
435 posts 04-Jul-06, 07:49 AM (pst)

21. "RE: Compression readings extremely low"
In response to message #15

This is what the correct original valve spring compressor looks like.


Attachments

http://www.g741.org/dcforum/User_files/44aa800873b4a933.jpg



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Lifer
Member since 4-Aug-04
1140 posts 04-Jul-06, 09:28 AM (pst)

22. "RE: Compression readings extremely low"
In response to message #21

Thanks, Bill. I knew somebody had to have the right one.



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brianacarey
unregistered user
03-Jul-06, 08:10 PM (pst)

16. "RE: Compression readings extremely low"
In response to message #13

Lane,
Here is the address of the one I have. I am sure people have better, but it might work.
http://www.sears.com/sr/javasr/product.do?pid=00947627000&vertical=Sears&BV_UseBVCookie=Yes

Copy and paste.

Jason




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MSeriesRebuild
Member since 3-Aug-04
1461 posts 03-Jul-06, 08:59 PM (pst)

18. "RE: Valve spring compressor"
In response to message #13

You can get a correct reasonably priced valve spring compressor for use on L-head engines at NAPA. There is a possibility you could unstick them, but you can't do a proper clean up job in the guides with out removing them. The job is much easier if the manfold assembly is removed. It's also very easy to spot leaking valves, if the manifolds are off. The test will need to be done at night or in a VERY dark area during the day. Rotate the engine to TDC at compression when both valves would be closed on any cylinder. Turn off all lights, place a good lighted flashlight tightly against the intake port, then the exhaust port for that cylinder. If there is even a slight leak you will see light around the head of the valve. Progress through all 6 cylinders with this test, based on the info. you have shared, I believe you will likely see the reason for the low compression problem. Valve guide bore brushes are available at NAPA to clean up the guides. Once they are clean, insert the valve back into the guide & check for proper clearance. If it's excessive in accordance with the specs. in the manual, you'll need to replace the guide & the valve. The exhaust seats are replaceable in the field with the correct tooling. High nickel hardened seats designed for use with unleaded fuel are available. The intake seats are not replaceable as the seat is machined into the block deck. Machining can be done & new intake seats installed, but the engine block will have to be stripped & sent to an engine machining facility to perform this. The guides can be replaced in the field also, but you must have the proper guide drivers & reamers to perform this task. Guide reaming is a must after installation as in most cases the guides will mushroom slightly from the driving process. Trying to do this without reaming will likely cause you heartache. If you have to use force such as a puller to remove the valves, forget trying to re-use them, they will be warpped. Do it right, do it once. If I can help with further questions, feel free to give me a call at the shop, 704-474-4683.
www.mseriesrebuild.com
Charles Talbert




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powool
Member since 9-Aug-04
95 posts 04-Jul-06, 07:27 PM (pst)

23. "RE: Valve spring compressor"
In response to message #18

I have read more than once that an intake valve would not normally need the hardened seat, since it usually runs at lower temperature. Do you feel this would be the case for the 230 as well? The context I've read that in was only for OHV engines, not L heads.
Paul Anderson



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MSeriesRebuild
Member since 3-Aug-04
1461 posts 05-Jul-06, 09:34 AM (pst)

24. "RE: Exhaust that takes the beating"
In response to message #23

This is pretty much the case as far as the bare necessities go. I would definitely change out the exhaust seats at rebuild time, no question. I guess I would say depending on how the truck will be used might determine the intake seats. If it's a hobby truck that will see few miles for many years, it would likely be OK to re-surface the intake seats & install new valves. If it's a truck that will see daily or frequent use, I would recommend doing them all while the block is in the machine shop at rebuild time. Doing the necessary machine work to install intake seats is to big of a job to tackle except at rebuild time unless you have a situation that makes it absolutely necessary.
www.mseriesrebuild.com
Charles Talbert




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