Sudden extreme loss of valve adjustment, did I break anything?

This morning I was trying to drive my Samurai to work, got the drivetrain problems fixed and all was going well. I also got a valve adjustment done. The engine was much quieter now. Maybe too quiet.

I'm driving along and my first sign that it would be going right back into the shop was that the quiet idle now had one noticeably loud valve. A minute later it's making loud putt-putt-putt noises and feeling "uneven" and I wondered how much longer I should keep driving. Then I heard some loud popping/backfiring noises coming from the engine bay and decided that I should keep driving for 0 seconds. I shut down the engine, coasted an impressive distance downhill and made an expert landing over a curb into an empty lot. Then I caught a bus the rest of the way to work. This marks the second consecutive time I've tried to drive the Samurai to work and had a breakdown.

So did I break anything?

Oh man the silence is deafening

I don't know how the adjustment works on a Samurai, but maybe you left an adjuster loose and it just backed off as you were driving? It might be fine, or it might have hammered the valve and damaged the stem or, less likely, the valve or seat. Hard to tell until you pull the cover...

I'll bet the valves were set to tight. the clue is how you said it was so quiet now. Things heat it up and expanded as they normally do, then all your valve lash was lost, holding one of the valves partially open. With manually adjusted valves it's better to be a little too loose than to be a little too tight. when it's just right it will sound a bit like a sewing machine.

If its just a valve adjustment problem, and nothing else was broken, it'll be just fine once its set correctly.

I'm pretty sure one of them did back off for some reason. Just dropped more than a Challenge budget on getting this engine fully rebuilt in October

Edit: And yes I'm thinking the adjustment was set too tight. It doesn't seem right for a G13A to be that quiet.

There's only one way to find out....

I agree that you probably didn't get one of the adjusters tight enough and the valve lost it's adjustment. I don't think it could be so far out of adjustment that it hit the piston. I had the same thing happened to me in an old MB diesel...didn't get the nut on the adjuster tight enough and it came loose and tightened up enough to hold the valve open. It ran like E36 M3, but was fine after readjusting. If the valve on my high compression diesel didn't hit the piston I doubt yours did either.

The G13A's a non-interference engine so at least I don't have to worry about valve-to-piston contact.

I just thought of something. You said the engine was rebuilt, was the cylinder head fully reconditioned? I'm wondering if you have a valve seat getting ready to fall out of the head casting. My Datsun pickup had that problem. The first symptom was that it had a few valves that would just not stay in adjustment no matter what I did. IIRC, the machinist put four new oversized intake valve seats in it to repair it.

That's worth looking into...but the valves stayed decently adjusted from the rebuild in October to today, so most likely that's not the problem. One of the adjustment screws did have to be replaced during the rebuild.

GameboyRMH wrote: Oh man the silence is deafening

10 min … seriously ?

When you think you might have wrecked a recently rebuilt engine and you're THIS far in the hole thanks to other automotive disasters, 10 minutes feels like a looooong time

How do the cam lobes look?

Pull the valve cover, reset them, go from there. When I do them I like to have the proper sized gauge out, along with the next size up and the next size down. Properly set, the big one will be very heavy drag, proper one light drag, and small one will go right through. That way there's no guessing about what "light drag" should be.

It's also possible you over tightened a jam nut and tore the threads out of something. I've seen the happen before, on a Yanmar marine motor with very heavy duty parts. They aren't supposed to be very tight (10ft lbs or so).

I broke a rocker arm once and it behaved exactly as you described. So I replaced them all. Then the lock portion of the lock nuts stopped working and I had to adjust valves again 300 miles later. Then again after 200, 75, 50, 50, 40... Miles on the same trip. Then I bought a second set of nuts and locked them in place.

OK got an update, the adjuster had backed off completely and the nut flew off, so it's a good thing I didn't try to drive any further. The fix was straightforward. The gaps were set to spec yesterday, turns out my engine was just unusually quiet when properly adjusted.

Was the nut recovered?

Kenny_McCormic wrote: Was the nut recovered?

Yes, the valve and piston caught it in mid air. Good thing too or it would have ran away.

HappyAndy wrote: when it's just right it will sound a bit like a sewing machine.

I think that's why the Brits call idle "tickover".

Kenny_McCormic wrote: Was the nut recovered?

Wouldn't have been a straightforward fix otherwise it was sitting right next to the rocker it came off of.

So I made it all the way to work today. 3rd time's the charm!