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JeepSaffer View Drop Down
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    Posted: 27 May 2017 at 2:32pm
I would appreciate some help from the wise heads on this forum, to advise me on my current L134 engine.

Mindful of the 95 Octane fuel we have here, and my understanding that this means you have to advance the timing to account for the slower rate of burn compared to the 68 Octane these little guys were designed for, I armed myself with a vacuum gauge, tachymeter/dwell meter, and set to work this morning. I connected the vacuum gauge to the inlet manifold at the vacuum port. 

My results are a little disappointing, and I hope that I can get some guidance as to what might be wrong, what to do about it, and the best way forward.

My stats: 
  1. Standard L134 go devil engine. Not rebuilt by me, but rebuilt at some unknown time in the past. Bored 0.06 over.
  2. NOS Carter 636SA carb.
  3. Newly gasketed engine, NOS carb gasket, copper head gasket. 
  4. Carb torqued down (but can't get my torque wrench in the space to set the torque... it's just "tight")
  5. Head torqued to spec and retorqued after getting to temp.
  6. All cylinders getting even compression of 87 PSI on a warm engine.
  7. Dwell set to 41 deg.
  8. Plugs gapped.
  9. Valves adjusted.
  10. I can get the engine idling OK at 800 rpm, but a little rough. 
  11. Oil pressure steady 40psi at idle. Engine temp around 160 deg F at idle.
  12. I am at 3,500 ft elevation.

My readings with the vacuum gauge are a little disappointing. When I adjust the distributor, I get a maximum of 15" Hg at idle of 800rpm, and the needle is jumping very rapidly between 13-15" Hg. By very quickly I mean it is just a blur. When I open and close the throttle quickly it will drop to around 2"Hg, then go up to around 18"Hg, and then settle back to 13-15"Hg. When I blip the throttle it will drop to 0, then up to 20", then settle back to 12-14". At 3000rpm it sits around 12"Hg, and although the needle is still not exactly steady, it has a much smaller range, say 11.75" to 12.25". 

My own research says that all good engines at sea level should read between 17-21"Hg, with 1" drop per 1000ft elevation above 2000ft.
If that is correct, and even working off the bottom of the 17-21" range, I should be reading at least 15.5"Hg.  So 13-15" seems definitely too low. And the rapid fluctuations of the needle doesn't look right...

Now for the fun part... the diagnosis! Smile

My own research says that lower than normal reading can mean worn rings, vacuum leaks or poor compression. Would a lower than normal vacuum reading with 87 psi compression confirm worn rings?
Rapidly fluctuating needle indicates possibility of weak springs, but needle fluctuation should INCREASE at 3000 rpm whereas mine decreases (becomes more steady)? 
A last note I found in my research suggests that "Fast Fluctuation between 14 to 19" Hg indicates worn intake valve stem guides". Can anyone confirm this?

I would appreciate anyone with experience in this to give me some pointers on what problem I likely have. I can do any other tests that you might need.

Mike

(Once I get some feedback on the most likely causes, my follow-on questions are going to be if there is something I can try without a complete rebuild of the engine (perhaps replacing worn valves guides?), or alternatively am I being too critical of this engine? Maybe it is a little tired and not as good as a freshly rebuilt engine, but still acceptable for a little while? Will I damage it if I drive it like this?)



Edited to correct the statement that timing needs to be advanced, not retarded.

Edited by JeepSaffer - 30 May 2017 at 4:01am
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Mark W. View Drop Down
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87 PSI on a warm engine is getting real close to the worn out engine range. Anything below 90 will show marked reduction in power.

I believe you are spot on with how you read your results. There are a very excellent charts on line that show how to read the results of a Vacuum test.

As to the 800 rpm Idle I would look for a minor air leak on the intake side. How is the Throttle shaft through the carb body? Its a well known wear point. If this is leaking or your gaining air somewhere else that idle should drop when fixed and the Idle vacuum should raise a couple points.

With an engine bored to .060" over you are just about at the limit of the block. Yes you can find .080" pistons but as I found out when getting ready to have mine machined its not the best idea to try cutting them out that far. SO you could be looking at Sleeving. Sleeves cost around $40-45.00 each here in the States and then you would have the extra boring to set them in place.

Thats my two cents on a Saturday morning
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Mike,

Base on your post I would look for a vacuum leak first.  I have had success with setting up an L134 at 2,000 rpms.  Take the engine up to 2 grand and turn the distributor  while watching the vacuum gauge.  Max out the vacuum and lock down the distributor.  Then adjust the idle screw and idle speed.

I will check the vacuum at idle to give you an idea of valued and bouncing.  I am at 800 feet above sea level here.  


Edited by Stev - 30 May 2017 at 2:03pm
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Thanks Mark and Stev. I will try your suggestion Stev, but will only get to it tomorrow. It is now 5:30pm here.

Originally posted by Mark W. Mark W. wrote:

 How is the Throttle shaft through the carb body? Its a well known wear point. 


It's a NOS carb, so it really can't be throttle shaft.

I have been watching some Youtube videos so I can see what a "good" vacuum test looks like. Most striking to me is that on a good engine the needle is very steady. On mine it is vibrating very quickly as described. The dead certain blame for this seems to be worn intake valve stem guides. Looks like that is definitely part of my problem.

New question 1: Will worn intake valve guides cause vibrating vacuum needle as the SOLE symptom, or will they ALSO cause low vacuum reading? ie if I replace the guides and valves will I only fix the needle vibration, or will I also improve the vacuum reading as well?

New question 2: Am I correct in saying that I can do a valve job without taking the engine out of the frame? Just the head and manifolds have to come off, right?
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I just answered my own question no. 2: Yes
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Mike,

I just checked two running L134 with the vacuum gauge.  At idle the vacuum gauge does not bounce.

My readings at idle were:

22 pounds of vacuum at 39 psi of oil pressure.
23 pounds of vacuum at 45 psi of oil pressure.

Yes, you can replace the guides and do a value job with  the engine in the frame.
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When you put the carb on did you use a brand new gasket between the carb and manifold? It has to be a good gasket with adequate tightness to crush the copper rings tight. Squirt some carb cleaner on it with the engine running to check for bubbles/leaks. This is a major vacuum leak point if not done properly. I only harp on this because this was my problem and it took months for me to figure out. I know everyone has given you sound pointers but that was another. May not be your problem but a good nugget to store away for future reference.
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Originally posted by damar2yxr damar2yxr wrote:

When you put the carb on did you use a brand new gasket between the carb and manifold? It has to be a good gasket with adequate tightness to crush the copper rings tight. Squirt some carb cleaner on it with the engine running to check for bubbles/leaks. This is a major vacuum leak point if not done properly. I only harp on this because this was my problem and it took months for me to figure out. I know everyone has given you sound pointers but that was another. May not be your problem but a good nugget to store away for future reference.


X2, remove the gasket and crush the rings in a vise, then re-install it.

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Thanks Dave and Lee for the pointers.

Carb gasket was NOS,meaning it doesn't have the copper rings. So nothing to crush!

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Originally posted by JeepSaffer JeepSaffer wrote:

Thanks Dave and Lee for the pointers.

Carb gasket was NOS,meaning it doesn't have the copper rings. So nothing to crush!


As the saying goes, never say never. IN THE OLD DAYS. (sorry I hit the caps lock). The OEM gasket came with the crush sleeves and it could be a pain to seal things.
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Originally posted by Unkamonkey Unkamonkey wrote:

Originally posted by JeepSaffer JeepSaffer wrote:

Thanks Dave and Lee for the pointers.

Carb gasket was NOS,meaning it doesn't have the copper rings. So nothing to crush!


As the saying goes, never say never. IN THE OLD DAYS. (sorry I hit the caps lock). The OEM gasket came with the crush sleeves and it could be a pain to seal things.

Well this is the carb gasket that came with the NOS carb. As I said, no copper rings to crush.



I have been reading every guide I can find on how to interpret vacuum gauge readings. One I found contained the following description:

Needle vibrating very rapidly indicates worn intake valve guides. How rapidly the needle vibrates indicates how many guides are worn. The needle will have less vibration at 3000 rpm than at idle.

These are my exact symptoms and I described them in my first post, even before I read that guide. So I am fairly convinced now that worn intake valves guides is my primary problem.

Interestingly, that same guide pointed out something that had escaped me initially, which is that worn intake valve guides are really allowing the introduction of crankcase air into the combustion chamber around the valve stem. So this really is nothing more than a vacuum leak, simply that it is an internal vacuum leak rather than an external leak. Looking at it that way, it is easy to see why my idling is also rough, and I am battling to set the mixture etc etc. It also answers my question above relating to if replacing the valve guides will fix not only the needle oscillations, but also improve the vacuum reading. It will, just as much as fixing an external vacuum leak will. Think of it, a vacuum leak not only in one place, but on each of four intake valve guides!

I guess I will be figuring out what is required for a complete valve job and then placing an order soon.

Thanks for all the input.

Mike
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Spray the carb cleaner anyway. Just make sure it ain't leaking there.
Here is another thing that bothers me. NOS means "new OLD stock" the key word here is old. Old things dry up . I would really make sure everything is buttoned up tight. I don't remember from the beginning of your build thread but this engine was running at the start right? Did it run good then? Nothing should really change from then until now except for all the new parts. Think through all that stuff first before you try the valve work.

Edited by damar2yxr - 28 May 2017 at 3:29pm
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As I look at that gasket I can see the laminations of the material. The glue that holds those laminations together can dry up and the air will get in through the laminations. If you ever meet me you'll notice the dents in my head from pounding it on the table after discovering this over the months of my frustration. It's often the stupidest thing.
Just double check that for me.
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I sprayed all around the carb,throttle, gasket and inlet manifold with carb cleaner, and no change in rpm.

Not sure if that's good news in my case   
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Will the engine run below 800 rpm with the choke out a little ?.. Also in your first post you mentioned retarding the timing due to 95 oct. fuel. I believe you need to advance it.

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You are quite correct on the need to advance the timing, rather than retard. I did in fact advance the timing.... just a slip up in the write up.

I have edited the original post.

I can get it to idle at around 700rpm by playing with the stop screw and the mix screw, but it is really rough and is always on the verge of quitting. Not what I would decribe as a "smooth idle".
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Is it possible that you distributor bushings are worn out?  How much side to side play do you have in the distributor shaft?  Remove  the distributor cap, the Rotor, and the dust cover.  Then try to wiggle the distributor main shaft,that the Rotor attaches to, from side to side.   There should not be any play.  Also check to make sure the rotor is not wiggling on the main shaft - it should be a tight fit.  Check the condition of the rotor and cap also.

If you want a perfectly smooth idle, the distributor needs to be in excellent condition.  Warn bushings will cause the engine to sound like a coffee percolator at idle even with a new cap and rotor.

Also ohm out the spark plug wires -  they should all give you the same resistance reading.  I think it is around 8 ohms or something close to that.  Set your meter on resistance / continuity put you probes on the ends of each plug wire.

When everything is perfect You can get it to idle at 400 to 500 RPMs.  Smooth like a well oiled sewing. machine.


Edited by Stev - 30 May 2017 at 2:32pm
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Mike,

Were you able to fix your problem? I'm experiencing the same symptoms as you and trying to figure out what it could be. 

Mark
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