New issue...again

[72Hardtop]

On the way home from work I was adjusting myself in my seat and let up off the gas. Upon returning my foot to the peddle to resume speed I noticed a slight stumble and heard what sounded like a muffled cough. Was going approximately 50-55mph when I felt/heard the issue. Bus continued to run good and was keeping pace without issue. When I exited the freeway I noticed the bus running rough. I pull over and give everything the look over and find nothing out of the ordinary. I continue home which was about another 2.5 miles (surface street) taking it easy. Parked the bus in my carport and let her cool down. After cooling down I proceeded to run down the check list.

1. Checked valve lash (all good with exception of #4 exhaust - .004)

2. Plug wires, rotor, cap and plugs all recently replaced (approx. 2000 miles ago) Bosch wires, NGK plugs

3. Pulled plugs all good except #4 appeared to have been fouled (fuel). Replaced with Bosch plug

4. Pulled all jets and cleaned passages as well.

Fired the bus up and it still runs rough. Shutdown. Loosen wires at cap and fire the bus up. Pulling 1, 2, and 3 cause bus to run worse. Pulling #4 no change. So I've narrowed it down to cylinder #4. Pulled the jet again and cleaned but bus still runs rough. At idle it will pop thru exhaust off & on. If I rev bus up 2500+ it seems to run great. I R/R the intake manifold gaskets approximately 5-6mos ago as well and its been running great until now. Engine has approximately 25,000 miles since rebuild in 2000. I'm thinking at this point it's time for a leakdown/compression test. Any other thoughts suggestions?

[RSorak 71Westy]

the problem is number 4 is not firing, to fire it needs compression, fuel, and spark at the right time. Figure out which of the 3 you're missing. Compression sounds like the next logical test.

[Amskeptic]

stumble and cough. running rough.
#4 exhaust - .004)
#4 appeared to have been fouled (fuel).
Pulling #4 no change.

Now you have a problem.
That cough is the moment that #4 lost a good valve seating.
Either it is an errant chunk of carbon not allowing the valve to seal, or the valve is burned or the seat is now loose.

You *can* remove the exhaust manifold/exchanger and look directly at the valve and seat. Put #4 at TDC. Now rotate the engine 270* clockwise. Look at the open valve. If the seat is loose, you will see a *margin line* of sorts between the seat and the aluminum of the port. Give it a little poke. If loose when cold, don't even start the engine again. Pull the head. If all looks contiguous and nice and whitish greyish brownish, put #4 at TDC and remove the plug. Stick a funnel-equipped small hose into the cylinder and pour some solvent down into the cylinder (diesel would good). Go look at the exhaust valve. If it is drooling wet, pull the head.
Colin

[72Hardtop]

stumble and cough. running rough.
#4 exhaust - .004)
#4 appeared to have been fouled (fuel).
Pulling #4 no change.

Now you have a problem.
That cough is the moment that #4 lost a good valve seating.
Either it is an errant chunk of carbon not allowing the valve to seal, or the valve is burned or the seat is now loose.

You *can* remove the exhaust manifold/exchanger and look directly at the valve and seat. Put #4 at TDC. Now rotate the engine 270* clockwise. Look at the open valve. If the seat is loose, you will see a *margin line* of sorts between the seat and the aluminum of the port. Give it a little poke. If loose when cold, don't even start the engine again. Pull the head. If all looks contiguous and nice and whitish greyish brownish, put #4 at TDC and remove the plug. Stick a funnel-equipped small hose into the cylinder and pour some solvent down into the cylinder (diesel would good). Go look at the exhaust valve. If it is drooling wet, pull the head.
Colin

I was kind of hoping for the best but expecting the worst. I've been leaning heavily toward a loose valve seat since the valve only snugged up at this point. Losing it's compression around the seat itself. Thatsall it takes. Could be a whole lot worse.

Going to do a compression test on Wednesday morning. Spoke with someone who suggested getting heads from Jerry at Northwest Connecting Rod. I've not had any dealings with any of the builders up here. I do know he uses the AMC castings but not sure what he's doing to the heads beyond that. Anyone have info as to what (if any) Jerry does to the heads?

All my contacts are in California. The few I know there are good (Fumio, Tuttle, Adrian) and of course there is also Jake. What's the going rate for replacement of heads including labor these days? Low vs high?

[dtrumbo]

Jerry is a great guy and does excellent machine-shop works so if Jerry's reading this please know I hold you in the highest regard. That said he "stakes" (I hope I remembered the right word he used) his valve seats. He was very proud of that fact as he showed them to me on another customers heads. I was warned-off of this method by others I trust. I know nothing for myself, only what others who have earned my trust have told me. I had my heads rebuilt by Adrian who does not use this "staking" method. The price for rebuilding my heads was $775.00 which included new valves, seats, guides, exhaust studs, three-angle grind and return shipping.

[72Hardtop]

Compression on #4 is ZERO. Looks like new heads it is. While I got the motor out I'll have both front and rear seal replaced and have the clutch checked. I may as well go ahead and replace the oil cooler seals as well. Anything else I should check/replace while engine is out?

I'm going with either Jake or Adrian for heads. Just e-mailed Adrian and waiting a reply.

Anything need to be done prior to head install such as redo deck height check, exhaust manifold alignment etc...?

[Amskeptic]

Compression on #4 is ZERO.
Anything need to be done prior to head install such as redo deck height check, exhaust manifold alignment etc...?

YOU are going to answer that one .....
Colin

[hambone]

Bummer man. Might as well check other things out while you have the engine out.

[SlowLane]

I'm going with either Jake or Adrian for heads. Just e-mailed Adrian and waiting a reply.

Len Hoffman does all of Jake's heads. You can contact Len directly here

Anything need to be done prior to head install such as redo deck height check, exhaust manifold alignment etc...

All that, and do a meticulous job of cleaning up the casting flash on your new heads.

[72Hardtop]

Update:

I contacted Jake for heads and only issue is...wait time. 1-3 months

So I'm going with Adrian who'll have them sent in 1 week. Head will be new AMC castings 42x36 valves all new hardware installed (Tool steel exhaust seats, SS valves, Chromolly intakes, SIL Brass guides etc..) Once heads arrive tear down will begin. I'm also going to replace both front & rear seal, have deck set, 911 adjusters installed, check clutch and also fix a small leak at the oil filter mount gasket. Heads come with 55cc chambers. Will update soon.

[Sylvester]

I did not know Len was in Athens Georgia, just a couple of hours from me. Does anyone know if he does type1 heads?

[Amskeptic]

I did not know Len was in Athens Georgia, just a couple of hours from me. Does anyone know if he does type1 heads?

I didn't either, and I am curious too. I have used heads in the back and some questionable new Italian exhaust valves that may be installed in the next few days.
Colin

[72Hardtop]

With regards to the deck height...the new heads according to Adrian will bolt on with stock CR 7.3:1. I'm pretty sure it was set up originally with shims to 8.0:1. I guess at this point I'll need to confirm the deck again and make adjustment/s accordingly? As for any adjustment that may be needed. I'll need to slip off the cylinders for that? If I do that I may just go ahead and re-ring it. What are you guys using to seal the cylinder bases up with? I was thinking...Permatex Aviation or Curil-T.

Working on the carbs now (40IDF's).

[dtrumbo]

When Adrian did my heads he included .060 cylinder shims and said by using them I would have 7.4:1 CR. Of course he would know the combustion chamber volume of the heads he worked on, but how on earth he would know the other variables in the equation is beyond me. I ended up needing .020 shims and have a nice set of .060's that will live forevermore in my parts box. The engine assembler must measure deck height, combustion chamber volume (including piston dish if applicable) and use the appropriate shim (or not) as necessary.

I used Permatex Aviation on both sides of the shim. Won't know for awhile ('til it's running!) how good it works.

[ruckman101]

I slipped the thin paper gaskets under my cylinders, but that was it. Nothing else. Looked like someone used blue permatex in abundance on the SP I just got into Bertha. It was goobered up real sloppy.

CR? Don't remember on the 1641, but no shims or adjustments, if I recall it was on the high side of seven, but under eight.


neal