I've just installed a newly rebuilt cylinder head but am having trouble getting the engine to run. The car will start and will run (somewhat roughly) if the throttle is actively operated but it will not idle. I'm pretty sure the ignition timing is proper and I've set and checked the lash 3 times. The head installed is not the one I removed from the engine but from the same SV engine type. Any suggestions where to look - I've exhausted all of my limited mechanical knowledge and almost all of my choicest swear words. Thanks.
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New Cyl Head - Won't Run
- Thread starter johnd
- Start date
RootesRich
Donation Time
Two things come to mind...
Double check your spark plug lead connections and look for a vac leak, especially between the intake and cyl head.
Double check your spark plug lead connections and look for a vac leak, especially between the intake and cyl head.
H One-Twenty
Donation Time
I'd start with checking the firing order, then look for air leaks/disconnected vacum hoses from the intake manifold (booster hose, distributor vacuum pipe). Will it run any better/worse when you use the choke? Might be worth checking the compression if you have the tools, but I'd bet on it being a fuel or ignition problem.
Hope you get it sorted out
Hope you get it sorted out
H One-Twenty
Donation Time
Ha ha, Rich was faster on the keyboard than me by a whole 4 mins.
Thanks guys - I really appreciate the help. I did attempt to hook-up a vacuum gauge yesterday but because of interference between the manifold port, Weber carb housing and gauge fitting I couldn't be sure if I had a good seal around the port. The gauge reading, however, was extremely low. I'm going to try to find an elbow fitting today that will give a good connection and try another reading. The manifold gasket was brand new and I was careful (at least I think was) when I installed the manifolds - hard to believe it is leaking.
kwhite
Donation Time
I had exact same issue on engine and head rebuild. My culprit was crankcase vent tube so I weigh in with those suggestions in previous posts. After 100 or so rough running miles to get it right and over 2,000 super smooth miles on rebuild, a faulty release bearing has everything out again. It is always something!
Try pinching off line while rotating distributor which worked for me by accident. Good Luck.
Try pinching off line while rotating distributor which worked for me by accident. Good Luck.
mccormac98
Gold Level Sponsor
Just to confirm, did you adjust the valves?
RootesRich
Donation Time
I'm not dismissing by any means, just stumped on the troubleshooting sequence (and trying to learn something today
)How would advancing and retarding the timing have any effect on the crankcase vent and identify the blockage?
That being said, verifying there are no impasses in the crankcase vent system is a solid suggestion.
kwhite
Donation Time
The best guess I have is that the inner diameter of the hoses I used to replace were different from original.
My experience was that when I slowly rotated ignition timing and gently pinched tube from oil filler neck, idle evened out. My temporary fix was adjutible clamp on that line. Perhaps permanent fix will be in place when I reinstall motor.
It deffinitately seemed to me to be "air" /vacum related rather than fuel or fire.
My experience was that when I slowly rotated ignition timing and gently pinched tube from oil filler neck, idle evened out. My temporary fix was adjutible clamp on that line. Perhaps permanent fix will be in place when I reinstall motor.
It deffinitately seemed to me to be "air" /vacum related rather than fuel or fire.
Yes - I did set the lash - at least 3 times. I set inlet/exhaust at .012/.014. The PO claimed that the car has a Holbay cam but I'm skeptical of that claim. (I understand the setting for Holbay cams is different.) I set the lash on the old head at .012/.014 and the car ran OK at those settings.
RootesRich
Donation Time
Now I'm even more confused (which isn't that unusual). If the hose from the oil filler housing is run correctly, that is, it is connected to the air cleaner of the carb, this has no effect on vacuum as the gasses entering the carb are subsequently metered by the carb itself. Effectively all you did was raise the idle speed of the engine by increasing the timing. Pinching that specific line off does nothing at low rpm. Perhaps your issue all along was the timing was too retarded.
The crankcase vent hose runs from the engine to the intake manifold and vac is controlled by a one way valve. If there was an issue with the valve, then I could see how pinching off that line could have some effect on the engine.
John, I would suggest that you verify static timing and the plug leads and put fresh clamps on all the vac hoses. Start the car and raise the idle speed up to where it will idle. Then I'd spray around the manifold gasket with soapy water to see if you can find a leak. I know you stated you used a fresh gasket, but I lost count of how many guys I know did the Weber conversion, used a fresh gasket and contacted me when their car ran like crap. The new intake gaskets seem to be of very poor quality and leaks are very common.
Nickodell
Donation Time
I believe Rich Vose's diagnosis - air leak - nails the most likely culprit. This will still allow the engine to run at large throttle openings, since the manifold vacuum (technically not vacuum, but depression) is very low and will suck in much less air than when the throttle is closed, or nearly so. I had the same problem after doing a head job on Matilda; the engine would work great at large throttle openings but die when I lifted up on the loud pedal, as the engine sucked in lots of air and weakened the mixture below a combustible one.
It was a PITA to fix, as a new gasket didn't do the trick, nor would adding Permatex. This was perplexing, as a steel rule on the manifold and head showed no warping. My final solution was to make a thicker gasket out of a roll of material from Pep Boys, tracing out the openings and cutting them with an Xacto knife. After that, all was well.
If you block off all other possible air leaks, such as manifold ports, and the trouble remains, that would be my guess.
It was a PITA to fix, as a new gasket didn't do the trick, nor would adding Permatex. This was perplexing, as a steel rule on the manifold and head showed no warping. My final solution was to make a thicker gasket out of a roll of material from Pep Boys, tracing out the openings and cutting them with an Xacto knife. After that, all was well.
If you block off all other possible air leaks, such as manifold ports, and the trouble remains, that would be my guess.
Thanks Rich & Nick and everybody else as well. The first thing I intend to do tomorrow when I get back at it is check for a vacuum leak around the intake manifold and carburetor base. I only have one vacuum hose that runs from the carb to the distributor. I've never clamped it before - I'll try that as well.
RootesRacer
Donation Time
The one that goes for the vac advance should not need a clamp as it should not make any vacuum with the throttle closed.
Should be a nice tight push at each end of hose.
Your vacuum leak will be a far more gross leak, like a leaking gasket or faulty PCV valve.
Nickodell
Donation Time
I remember years ago, when I was a member of Tigers East/Alpines East, Tom Ehrhart ("Tiger Tom") saying to get rid of the PCV valve as with the small number of Alpines in use they don't make a pin's worth of difference to the planet's atmosphere and are a constant source of trouble.
RootesRacer
Donation Time
The purpose of PCV is your engines benefit, not the environment.
PCV causes a flow of clean air through your crankcase so blowby gasses are prevented from fouling your oil (which causes sludge and oil acidification).
PCV alone is the reason that in the 60s, engines went from a 50,000 mile service life to over 100,000 miles.