4.0 sohc experts, timing chain question.

[bradb460]

I'm in the process of getting another engine ready for my 00 xls before the timing chains start rattling. The engine I'm working on supposedly only has 88k on it, but who knows. My question is: with a new chain and sprockets and new guides how far should the tensioner be compressed? I'm talking about the rear chain. Thanks

 

[Tech By Trade]

Just pull the passenger valve cover and have a look. By far the easiest way to check.

 

[bradb460]

What I mean is I have replaced the guides on the rear timing chain and the tensioner is only about 3/16" from being fully extended, so I'm thinking the chain is stretched also.

 

[Tech By Trade]

Wow, you went through all the trouble of changing the guides and didnt change the gears and chains while you were in there? I didnt think you could even buy the guides anymore. I thought you could only buy a kit with chains gears and guides.

 

[2000StreetRod]

depends on valve spring compression

The distance the tensioner is extended depends on which valve springs are compressed and how much. If the crankshaft is rotated the piston will extend and retract as the camshaft lobes depress the cam followers compressing the valve springs. Did you use the OTC 6488 timing tool kit to time the camshafts? That's the only reliable method to set the camshaft timing correctly. Piston 1 is locked at TDC and the tensioner tool from the kit applies the proper amount of tension to the chain. The chains are very strong. I doubt that they have stretched.

 

[bradb460]

Wow, you went through all the trouble of changing the guides and didnt change the gears and chains while you were in there? I didnt think you could even buy the guides anymore. I thought you could only buy a kit with chains gears and guides.

The engine is on a stand, it's pretty easy to change just the guide on the stand. I have the new chain and sprockets and will use them if they need replaced.

 

[bradb460]

The distance the tensioner is extended depends on which valve springs are compressed and how much. If the crankshaft is rotated the piston will extend and retract as the camshaft lobes depress the cam followers compressing the valve springs. Did you use the OTC 6488 timing tool kit to time the camshafts? That's the only reliable method to set the camshaft timing correctly. Piston 1 is locked at TDC and the tensioner tool from the kit applies the proper amount of tension to the chain. The chains are very strong. I doubt that they have stretched.

So you're saying the tensioner is constantly moving in and out as the engine is running?

 

[2000StreetRod]

spring vs hydraulic tension

So you're saying the tensioner is constantly moving in and out as the engine is running?

The tension will move in and out when the crankshaft is rotated by hand but much less so when the engine is running. The spring in the tensioner is weak compared to the hydraulic pressure when the engine is running. The precision tensioner tool in the kit is a fixed length that will make the chain taught on both the traction and slack sides of the chain. If the camshaft is timed with just the tensioner spring pressure the chain will not be taught on the traction side. The amount of slack in the chain correlates to how far off the timing will be. However, it probably is less than a few camshaft degrees which is doubled for crankshaft degrees.

 

[bradb460]

Ok, I went back out to the shop and farted around with it a little more. I went ahead and knocked out the plug behind the jackshaft so I could get the lower sprocket off. I put the new chain and sprockets on and things look much better. with the drive side of the chain tight the tensioner is only 1/3 of the way out. So the old chain is stretched some.

 

[bradb460]

Does anyone know where to get a new block plug that goes behind the jackshaft?

 

[2000StreetRod]

jackshaft rear plug

Cover assy/rear of block jackshaft opening plug F77Z6026AB
Its probably only available from a dealer.

 

[bradb460]

Thanks!