M151a2 engine question.

[elkhtr]

Getting familiar with the new addition but have run into something I haven't seen before.
On cold start the engine generally fires right up, but within about a minute it begines to smoke blue.
After about five to ten minutes of running it clears and doesn't smoke any more as long as warm.
Once it quits there is no noticible smoke when accelerating, or after an in gear deceleration.
Any of you 151 guys run across this?

 

[Whiterabbit]

Yea, mine kind'a does that. I get a lil blue smoke at startup and acceleration till it warms up, stops within a min or two. Probably a little leak down past the valve stem seals while sitting. My engine probably only has less than a 1,000 miles on it.

 

[elkhtr]

Yea, mine kind'a does that. I get a lil blue smoke at startup and acceleration till it warms up, stops within a min or two. Probably a little leak down past the valve stem seals while sitting. My engine probably only has less than a 1,000 miles on it.

Does yours smoke right away at startup, or does it have a delay also?

 

[Jeepsinker]

That's is certainly exhaust valve stem seals. Could be guides but not nearly as likely.

 

[elkhtr]

That's is certainly exhaust valve stem seals. Could be guides but not nearly as likely.

Looks like another thing on the menu.
Cant stand a smoker, unless its diesel.

 

[Westech]

You can use high mileage motor oil (seal and gasket rejuvenator added) and that may help with out a seal change out.
The engine gasket/seal kits are under 80$ so it's a cheaper fix.

 

[nattieleather]

Also these motors run better if you pull the choke about a 1/4 inch. Most folks pull the choke out start it get it running and then push it all the way in, but the M151 needs the choke out just a little. I always use to pull it out about a fingers width when I had mine.

 

[Whiterabbit]

I get a lil' smoke at startup only. I guess the stem seals might be a bit hard from sitting 12 years. I'm not worried about it, at least i know the valves' stems are well oiled. You'll get just a lil' bit of smoke on downshift slowdowns because of the high vac in the intake sucking oil past the seals.
The truck's carb sucks. Too lean. They need a bit of choke to run right. You can find the sweet spot by taking off with no choke and doing it again with a hair bit of choke then a bit more till the stumble goes away. Remove the rubber intake hose and note the choke plate angle. Loosen cable connections and set up the choke knob so that when it's all the way in the choke plate is at that angle the engine likes.
I'm a FNG with the 1/4tn too. I've only had mine together since May. BUT I LOVE THIS TRUCK! Before that if I had problems with a M151A2 I'd tell the motor pool mechanics. (in the late 80's)
If it goes away when it warms up I wouldn't sweat it. You can probably go many thousands of miles before it starts smoking constantly.

 

[Jeepsinker]

If it has to have some choke to run right the carb is not properly adjusted.

 

[Whiterabbit]

Not really. It's even in the manuals about leaving the choke out a bit. It's been beat to death about the whole needing a little choke on G838 by guys who have been messing with these trucks for countless years. Now if you need alot of choke then your idle jet is clogged or your idle mix is off but that will show up as ruff idle and an even/steady low manifold vac reading. It's just Uncle Sugar had the carb set very lean and the jetting is a little on the small side to make the EPA happy. If the carb is clean and in good working order the only thing you can mess with is the idle mix screw and the idle speed. One guy over there has up drilled his jets and claims good results and no need for a lil choke.

 

[poppop]

whiterabbit is right, it is well documented that the choke has to be out for them to run right. Military mechanics used to set them as described above because some of the young drivers did not understand this and it was easier to set the choke so the driver could push it all the way in and still have it choked some. You are right it is to lean but no way to correct it. There is a rebuilder out there that claims to have that problem corrected on his rebuilt units.

 

[Jeepsinker]

Ok, I wasn't aware they aren't adjustable. I learned something today, which is good because I aim to get one eventually to add to my collection.

 

[Whiterabbit]

If you get the chance to get one then do. Yrs ago I thought I wanted a WWII jeep..... till I tried sitting in it! Looked for an M38A1 but they were all rotted from running back and forth in the swamps or Bubba'd and they still wanted too much. I literally fell into my A2 by luck. Stone cold simple, pretty tuff, great off road, half way decent gas millage for a military vehicle and tons of thumbs up on the road.

 

[Jeepsinker]

Oh it isn't a maybe. I will have one eventually, just have to find the right deal at the right time.

 

[elkhtr]

Well bad news.
Tore the carb apart to see if that would help its funky idle problem.
put it back together and it idled nice, still bucked and jumped at anything past half throttle or second gear.
Thought to myself, good time for a compression check.
I knew the #2 sparkplug wire was jimmy rigged, pulled #1 off and the end was missing.
the last two were good, no big deal.
pulled the spark plugs, two were over gapped and two were completely fouled.
Aha! found why it was running like crap.
Compression test, #1 125 smiling!
#2 0
#3 0
#4 120, punched in the gut feeling begins.
Pulled the valve cover, two pushrods off the rockers, one bent.
Pulled the side cover, one lifter laying in the gallery, cam end of lifter looks evil, like it broke off, not metal smeared small block chevy style.
The other lifter wont come out of its bore, hanging on a burr most likely.
Now what, rebuild, replace, anyone have an engine?
Cant believe it ran as good as it did on two cylinders.

 

[Jeepsinker]

Probably cheaper to find another engine. Of course a gasket kit is only $80, bearings can't cost much, so if lifters can be had and at a good price then I would yank it and build it.

 

[elkhtr]

Duh! looked at the manual, the lifters are not straight cylinders.
Apparently the cam has to come out to remove them.
So one is obviously broken.
Dont know why the one pushrod is bent, it wasnt riding on the broken lifter.
Oil pressure was good, and the valve train was wet when I pulled the covers.
Looks like the engine is coming out.

 

[Westech]

Sorry about the engine. Good thing is tnj Murray has a LOAD of them.
As the carb goes.... Drill out the jet to a wire gauge 55 and solved. Did that to mine a few years ago and she runs great!! No choke, starts right up, runs perfect. Side note is I run 91 or 93 octane with no ethanol and a lead additive, bumped the timing at idle (will very from engine to engine) and she loves it.

 

[poppop]

elkhtr, I just repaired an engine in an A2 for SS member grits with the same problem, only it was one valve. Check the valve adjustment screw in the affected rocker arms. They are supposed to be hard to turn and have no lock nuts. In Andy's engine that screw was real loose and backed out until the push rod jumped out of the rocker. It did not jump clear but bound up on the edge of the rocker which I think caused the valve to hit the piston. This broke the head off the lifter. It had run so long like this the broken stem had cut a quarter inch groove in the cam. I pulled the engine, stripped the front and held the lifters up and removed the cam and replaced the broken lifter and installed another cam. Also replaced the defective rocker. It runs like a champ now. Unless you have a bent valve from hitting a piston I think your engine is very repairable. I got Andy's parts from an engine I had bought for parts. I don't have another cam but I do have the lifters and rockers if you need them.

 

[nattieleather]

The motors are fairly simple to work on. Heck I replaced the water pump in the field one afternoon. Another time a friend and I were near DC when we dropped a valve in #1 cylinder. Had another friend UPS us a take off head and gaskets put the new head on in a snow storm and drove the little truck back to Cleveland Ohio with no problems. Motor ran hard as his daily driver for another two years. Get the -34 and -34P manuals and go through it and find what needs to be fixed and just rebuild it. If you have good mechanical skills might take you a week or less. I've seen these motors run on two cylinders and still have power. They are tough little motors. Respect the 151...