Timing jumping on 152

N

natefank

Member
So im having trouble tuning my Scout 80 with a 152. So I was trying to get it tuned today and noticed that the timing would hold solid when I had it at about 2500 rpm at about 20* btdc then all of a sudden it would jump to like 10* atdc, then go back to 20* btdc. What would cause this? The distributor was just rebuilt, same with the carb. I couldn't find any vacuum leaks. I set the carb with a vacuum gauge so I know that is correct, and the timing is set. I just don't know what is causing the jumping. Thanks
 
Disconnect and block the vacuum advance. The mechanical advance also comes in at rpm above 800 rpm idle. Set the initial timing to 10-12 while idling at 500.
 
The manual says to set timing at 4 at 500 rpm idle. But that also doesn't help the fact that the timing is jumping.
 
That's just a starting point. You can dial in some additional advance with no problem. Plugging off the vac advance line May prevent the timing from jumping around which is why he suggested it.
 
natefank said:
the manual says to set timing at 4 at 500 rpm idle. But that also doesn't help the fact that the timing is jumping.
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Well in that case look up " why is my timing jumping in the manual". :lol:
I gave you a test to run and depending on the outcome I would have recommended a next step in the process. I guess you want a magic fix all statment. You aint going to get it in one single easy step. There are a few possibilities to what you are seeing. One is a hanging vacuum advance. Another is a wonky dizzy rebuild. Still a bad set of cam bearings. I thought the simple possibilities are the first.
 
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Ok so I messed with it today and my mechanical advance wasn't working so I messed with the springs and got it real close to where it should be advancing but I'm still getting sporadic jumping of the timing. Any other ideas? The distributor was rebuild by the philbin group, which was recommended by people on binderplanet.com.
 
It wasnt messed up, just the springs were wayyyy too tight so it wasn't advancing. Like I said tho, I got em working but it's still jumping all over the place
 
How's it running while the timing is jumping 30*? You should experience major changes in run quality. Will it stabilize at any rpm?
 
So I thinks it's something internal on he engine. It started making a noise that was coming from the cam/crank area. Anyone wanna buy a Scout 80?
 
Time to drop the oil pan for a thorough inspection of the the bottom end. I know this is frustrating. If it turns out that some component of the engine has been severely damaged, replacement 152 engines in running condition are fairly plentiful and can generally be had quite reasonably.
 
About the only inernal situation that could come and go would be the cam moving fore and aft. The can has a locating plate held inplace by two flat head screws. It guides the cam on the back side and the cam gear on the front.

The pan is easy to pull takes about 30 minutes. Then you can take a look at the gear situation. Even pulling teh fromt cover is quick. Again with or without the pan that is fairly quick. Don't give up on the old lady just yet. :icon_sad:
 
So after getting some ideas from another site I believe it is the cam gear. I can move the crank about 5-6* back and forth without the distributor moving.
Robert: the locating plate you are talking about, I can get to it from the oil pan? I tried taking off the timing cover but I only got as far as getting the crank bolt out, I need a puller for the pulley. What should I be looking for when I pull either covers?
 
natefank said:
so after getting some ideas from another site I believe it is the cam gear. I can move the crank about 5-6* back and forth without the distributor moving.
Robert: the locating plate you are talking about, I can get to it from the oil pan? I tried taking off the timing cover but I only got as far as getting the crank bolt out, I need a puller for the pulley. What should I be looking for when I pull either covers?
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With the timing cover off, it will look almost like this, only without the left bank of cylinders & left cylinder head.
 

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Get the crank bolt out.sometimes the dampner will come off w/a slight tapping w/rubber or hard plastic mallet.Jeff( leave the pully's on to tap)
 
So I got the timing cover off, everything seemed ok, the only thing I found was that the timing on the gears were off about 2 teeth. Would that be the problem? And the plate for the cam was tight and there was no movement in the cam. Any thing else to look for?
 
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