Tractor sounding '02 - Help!

[NicholasMav]

I'm at a bit of a loss folks, and could use some expert advice.  

Backstory: 2018 engine rebuilt (block re-bored, new pistons, new oil pump, chain tensioner...all the things), took some massaging over the years with help from friends, but had been, if not perfectly purring along, pretty darn close to it.  This past November did a long drive with the local Gearbuster crew with no issues.  Sometime in December '23 on a nice day I took it for a drive and was having a blast. Turned up a steep hill and halfway up it started making an odd popping sound.  Kinda muffled, and only on acceleration/under load, but loss of power was evident.  I limped it home, thankfully only about a mile away.

 

Once I had some time to dig in again it seemed to be coming from the carb.  See first video below (that "fupfupfup"on acceleration).  Once we pulled off the air filter it was much louder and prevalent.  

 

 

Another friend (shout out to all these folks to who take time to help!) offered a known working 32/36 weber, just like mine, to try to rule out that it's my carb.  Same issue, maybe ran worse.

 

Next steps: Re-established it was at TDC, based off both crank pulley/pointer and 1st cylinder rocker arms were off lobe.  Upgraded camshaft didn't have machined marking, but once other two TDC checks were nailed down, I did see a faint "scratched" mark just off-center from oil bar.  See pic:

 

Checked plugs and they were good, checked distributor and it was aimed at line stamped on the rim indicating #1 position, plug wiring was checked to be in correct order.  Distributor still at the mark we created before tearing the engine down, and after many adjustments to find best position, that mark was still best.  While in there I did a valve adjustment, slapped it all back together and gave it a try. Video below is with that known-good, borrowed carb...seemingly quite a bit worse, wouldn't run without messing with accelerator.  Very Tractor-like.  

 

 

Ideas?  Have a messed up something mechanical? Could the chain tensioner allowed the chain to skip a tooth or two? And is that why that faint scratch mark is off-center from oil bar?  Any other ideas?  I'm all ears!!

 

Thanks in advance!

NM

 

 

[kbmb02]

Have you done a compression test? 

[Son of Marty]

2nd the compression test. It looks like you have a valve problem but a bit more info is needed for that.

[Mark92131]

14 minutes ago, NicholasMav said:

Turned up a steep hill and halfway up it started making an odd popping sound.

 

When was the last time you changed your fuel filter?  Sediment in the filter settles back on steep hills and can starves your carb of fuel.

 

Watched the movie, your timing seems way off.  Loosen the 10mm nut at the base of your distributor and have a helper slowly turn the distributor housing counter-clockwise (more advance) while you try to start it.  It should catch and run.  Compression test would be useful.  If it has good compression, then either ignition or fuel delivery.

 

Mark92131

[02Pilot]

The circumstances of the failure sound a lot like when I burned an exhaust valve in a Saab 900. A compression test is definitely a good idea.

[Dudeland]

Dude, no bueno. Valvetrain.  I think you should look at the exhaust side.  I expect that if you lost a seat, you would hear it way more tic.   Maybe. something bent. 

 

I wouldn't run it too much just in case it became catastrophic.  How old is your chain tensioner?   Confirm the timing chain position and compression. I expect you will find something.   

[OldRoller]

Intake valve issue. Compression test will confirm. Broken spring on the associated cylinder?....

[NicholasMav]

Thanks all! I'm going to grab a compression test kit and let you all know what I find.  ...to be continued.

[NicholasMav]

2 hours ago, Dudeland said:

How old is your chain tensioner?   

Chain, tensioner, all parts that wear were replaced at rebuild in 2018.  So not near old enough to die this soon...I don't drive it a whole lot.

[NicholasMav]

4 hours ago, Mark92131 said:

 

When was the last time you changed your fuel filter?  Sediment in the filter settles back on steep hills and can starves your carb of fuel.

 

 

Mark92131

The one that's on there I replaced last summer, so it's new.   Will try compression test ASAP.  Timing was fine prior to this incident, and I have messed with it since the incident and it makes no difference turning it either way.

[resra]

Sounds really like running on two cylinders. If the compression numbers come out healthy, my money is on your distributor. If you have a spare known good distributor then give that a try granted engine compression numbers are healthy across all four bangers.

[Dudeland]

I am 99% confident that he lost the head gasket between two cylinders. 

[Mike Self]

4 hours ago, Dudeland said:

I am 99% confident that he lost the head gasket between two cylinders. 

I'm not sure I'd go with 99%,but I'd go with "high"...had that happen to me on the way back from a CCA Ofest in Wisconsin--same symptoms.  Managed to limp it to a garage where a compression test confirmed the head gasket blew between #3 and #4 cylinders about 50k miles into a rebuilt engine, due to a massive vacuum leak when a plug came off an unused vacuum port in the intake manifold.  Ended up having to dolly the car home behind a huge UHaul truck...how embarrassing!

 

Unless your chain tensioner suddenly died, it's unlikely that your dizzy or cam would suddenly jump time.  From that one camshaft picture it appears that the chain sprocket still has flat spots atop each tooth, so it's not excessively worn.  And a burnt valve (although not a loose valve seat) usually manifests itself over a period of time, not suddenly. 

 

Let us know whatcha find!

 

mike

[Mikesmalaga72]

After slightly snugging up my exhaust manifold the tractor sound went away.

[resra]

20 minutes ago, Mikesmalaga72 said:

After slightly snugging up my exhaust manifold the tractor sound went away.

 

Not this one, you can clearly see the shake that poor thing is not feeling well on multiple cylinders.