timing

steven · Post by **steven** » Mon Mar 06, 2006 9:55 pm

When my LA 318 idles, I check the timing with a light and the mark I made on it doesnt stay in one spot, same at half idle or full. It sort of jumps around. Is the vacuum timing advance thingy plugged up, partially blocked, shot, or what? Anybody else have this problem, or is this normal, I would assume it isnt.

Thanks

Steve

JimE · Post by **JimE** » Mon Mar 06, 2006 10:06 pm

Did you tighten down the distributor hold clamp? As you increase rpm it should go up if the vacuum advance is working properly. Jim

PwrWgnWalt · Post by **PwrWgnWalt** » Tue Mar 07, 2006 1:13 am

Steve;

Not knowing anything about how much "mileage" that 318 has, or it's lineage, I'll offer this:

A 'jumpy' timing mark is often indicative of a worn timing chain.

If it has (or more appropriately - "HAD") the dreaded "nylon covered teeth" on the cam gear, this is likely the root of the problem.
Over time, these nylon teeth became brittle with exposure to oil, acids, and heat. I have yet to see one intact - except in the pictures. The metal underneath is usually ok, but by the nylon chipping away, it leaves the timing chain sloppy as a ... well, you know what I mean.

I don't profess to know when they used these, just know they did. I suspect it was after (or close to the end of when) these trucks were minted, but if your engine is a later year, or ever had it's timing chain replaced... this might be it. Could also be that the stock metal gears and chain are just worn.

Of course, the "no advance" symptoms you tell about are a separate issue and could be a bunch of other stuff, too. Make sure the vacuum can on the distributor is working (if you don't have a little handheld vacuum tester, have someone put vacuum to it while you read the timing mark). And make sure it's in the right Carb port! Check the easy (read: non-invasive) things first - like vacuum leaks, carb mounting, etc. Spraying some engine starter fluid at key points while the engine is running (and cold yet) is one good way.

BTW - the timing marks usually stabilized some at higher rpm's.

PwrWgnWalt

steven · Post by **steven** » Tue Mar 07, 2006 9:05 am

Yes I did tighten the clamp. It does advance, but its just jumpy. The motor has 90k on it, original, so it very well could be the chain and sprockets. What should the timing be set at? Should it be set at low idle or high? Thanks for the responses.

Steve

duracell · Post by **duracell** » Wed Mar 08, 2006 4:31 am

could a worn distributer be a cause as well