M38A1 engine noise

[Amer-team]

Time for the guru's to chime in. It has a sound like a tailpipe rattling on something. Checked that and no noise changes. Put the stethescope on it and the noise sounds like it is coming from the timing chain cover. No noise at the water pump or fuel pump.

could I have a loose timing chain? Other ideas? This jeep has about 13,000 miles on it with no major engine work being done.

Ideas? Thank you for your thoughts in this matter.

 

[zout]

Make sure the crank nut is at torque - could be the oil slinger inside the timing cover that is light metal tinging around in there.

 

[wilfreeman]

Mine sounded like a rod knock - thought it was the exhaust at first, but traced it down to the generator vibrating on the motor mount. Turns out the belts I had on it were too long, causing the generator to touch the motor mount.

Just a thought

 

[Amer-team]

Thank you for the tips. Will check into both of those today. This vehicle has about 13,000 original miles and we did replace the front oil seal a couple years ago, but probably only a couple hundered miles. So something may not have been tightened properly.

 

[zout]

As WF was referencing to - see if the noise is RPM related to engine rotation or sort of an external thumping sound - there will be a difference.

This should help at least narrow down the problem.
Throttle linkage banging on the bellhousing.
Forementioned Slinger inside the timing cover.
WF's mentioned generator mounting.

 

[JGBallew]

Make sure the crank nut is at torque - could be the oil slinger inside the timing cover that is light metal tinging around in there.

Seconding this. Those 38A1 engines don't have a timing chain, so it's not a chain clattering.

Another consideration is the fuel pump, though you said you checked that.

 

[Amer-team]

Sound is definitely related to RPM, more RPM more noise.

 

[zout]

On the top end you will get a much more pronounced dead rattle sound than say the sound from inside the cover behind the exhaust manifold - I would then look these two area's to start eliminations. Maybe on the rebuild locknuts did not get secured @rockers @tappets.

 

[rodmayo]

My m170 does the same thing try taking dip stick out and turning 180 degrees.

 

[Amer-team]

Thank you for the tips and thoughts on this project.
The crankshaft pulley nut had backed off a bit. It takes a 1 3/8" something which I did not have. Once that was located, a little tightening and no more noise.
Zout mentioned torque on the nut. How do you lock the engine up enough to get torque on this nut? Is there a preferred method besides jamming something on a pulley?

 

[zout]

AHHHHHH your asking top secret ready to kill info there fella.

But seeing as you started your thread with asking help from ole timers - here is a hint and a clue.

The other end of your engine has a flywheel with TEETH on it - which will also allow a big screw driver to lock in on the teeth to stop movement.

A leather strap around the front pulley - but nothing metal will all you to get to torque (just like an oil filter strap wrench).

I could say jam a big arse screwdriver down one of the spark plug holes after removing a spark plug to stop the piston from coming up - BUt trust me - I am not that cruel - do not even try this.

Couple best ways to stop engine rotation are the top 2 - third is just insane.

Let us know when you got it nailed please

 

[Amer-team]

Thanks for the tips. I hoped there was something easier than the flywheel trick but was about ready to go with it. May try option 2 first.

Of course you forgot the one about pulling the plugs and pouring water in the holes, then putting the plugs back in to give it a hydrostatic lock.

I have had this jeep for 25 years and it has been trouble free. Have replaced the brake items, belts, and hoses and normal maintenance fluids, but it has been a great dependable runner and I had not run across this issue before.

Thanks again for the help. Mission accomplished. Time to pull the top and drive.

 

[zout]

Of course you forgot the one about pulling the plugs and pouring water in the holes, then putting the plugs back in to give it a hydrostatic lock.

I cannot even think of any enemies I would even have do this to a find piece of MV machinery - I think you are sicker than I am and that is hard to beat.

Will not take much holding on the crank pulley - I know you know to take it softly and get the idea - post results.

 

[JGBallew]

I used to bottom out a cylinder til just before the compression stroke and feed in some jute or similar natural fiber twine through the plug hole, then bring the piston up compressing the jute and locking the engine.

Made changing valve guide seals on a lot of engines much easier, as I didn't have an air compressor at the time.

You could probably do the same here, but I'd strongly suggest a natural fiber so any bits left in the cylinder will just burn up and go out the exhaust. (Plus, jute twine is dirt cheap).

 

[Amer-team]

That is an interesting solution. Someone will probably beat me, but I put it in low gear, set the ebrake, and put a bar through the yoke of the rear drive line. There was plenty of resistence to set the pulley nut.
Then I was on such a roll, jumped on taking the hard top off the 5 ton that had been on there for a number of years judging from the rusty bolts that were holding it together. About a third came out, the others were difficult. Will tackle the back vertical portion of the top tomorrow.

Thanks again for the advice and thougths on the M38A1.

 

[steelypip]

Let's see, in order of preference:

1. Put it in high gear and set the handbrake. This works pretty well up to 100 lb-ft or so if your handbrake works well. Low gear gives the engine more torque multiplication to the brake, so doesn't work as well.
2. Something stuck in the flywheel or flexplate to jam the thing. Just about anything works as long as you don't break or bend something important. Big screwdrivers and prybars work well.
3. A piece of rope down a spark plug hole. This works great as long as you're careful to make sure that you put the rope in on the compression stroke and slowly turn the engine in the running direction until the piston pinches the rope against the head and valves. It can take a surprising amount of rope on an open-chamber head. Never had any problems with nylon rope, tend to prefer it over jute or hemp rope because it doesn't leave loose fibers in the engine.
4. Locking the accessory drive belt. You can get clever with the generator or alternator pulley. Bending stuff is a problem here, too.