Quote:
Originally Posted by yuke
Well about 3 yrs. ago when I got the 85 300 SD a mechanic told me I should replace the timing chain because when he adjusted the valves he could see the chain tensioner was near the end of its adjustment to keep tension on the chain.I did some research on chain replacement and no place did it mention by looking at the tensioner that would dictate chain replacement every where said to measure stretch by either of 2 ways 1st lining up marks on cam tower I got 0 or 1 degree. The more precise way to measure by taking lash out of 1 intake valve then measureing the reading when the valve drops 2 mm or .078 which I did and again came up same reading 11 right on or 12 degrees . All the rails looked good the spring in the tensioner did show some wear and was about 1/4" shorter then the new one so I did replace that but think I am not going to replace chain as I do not see how I can better the readings I got. Looking from top of engine down the adjuster is sticking out about 1/4" against the tensioner rail. The car has about 300,000 on it but dont know the history on it. Like to hear some thoughts on matter. Oh and I really do'nt know why you would have to pull whole tensioner out when all you have to do is take center bolt out to take spring out and release tension when rolling a new chain in?
|
Some would view the replacement of the chain as insurance against the catastrophic ramifications of chain breakage. With 300,000 miles, I would probably side with that group.
You indeed have to remove the tensioner as the tensioning pin has grooves in the slide mechanism that only allows the tensioner to slide in and not out. There will be a couple milimeters of slide action allowed that you can see when the spring is released, but you will be unable to reset the length unless you remove the tensioner and reinsert the pin from the outside.
Note: when the tensioner is removed, ensure the gasket mating surface is clean and shiny prior to installing the new gasket. Kinda difficult to simply scrape it off; I ended up using a small die grinder with a scotchbrite attachment to polish it. If I recall, (but verify) sealant should be applied on the gasket to tensioner side but not the gasket to cylinder head. Others please chime in if this is not correct.
You indicate that the measurements show that the chain is not elongated, but also you don't know the history of the motor. It is possible that a previous owner went the route of an offset key on the top timing gear to bring the timing back to spec. This could explain the measurement being correct, but the tensioner being at its max insertion limit. Just a possibility, but personally I would have just rolled in a new chain as opposed to inserting an offest key. The offset key will bring the valve train back into time, but will still leave the IP slightly out of sycnh with specifications if the chain is elongated.
Mike