JonnyG, Even the ones that use hydralic pressure still have a spring. This is what keeps the tensioner from retracting when the engine is shtdown. Most also have what apears to be a rack on the back and a little cam. As the tensioner extends the cam locks down on the rack. This prevents it from ever retracting. If you try to do a cam swap on this design you have to use wedge tools to prevent their movment before removeing tension from the chain. If you do not the second you remove the cam sproctes they extend out. IF this happens you must remove the timeing cover and rest them or you will never get the cam sprokets back on.
THe other design uses spring tension to partial extend the tension and shoe. This ensures that the shoe is always in contact with the chain. Then once oil presure is up it increases the force that the tension puts against the chain.
If either one of these systems fail you would get one of two things. A ton of timing chain wip and clatter or it would jump a tooth.
Some systems combine all of these features. Only a moron for an engineer would depend solely on hydralic pressure to tension the chain with no provision for cold start lose of prime situation.
I suggest you go to your local parts store and check out a timeing chain tensioner. If you want one I know can be retracted with no special tools after extending it out use a 1995 Toyota Tacoma 2.7 I4. The lever to retract it is on the back side.
If you want one with no lock use 1986 4Runner it has a spring with no lock. You can push it in and out like a shock absorber. Both of the above use hydralic pressure as their primary force to provide tension.
[ May 12, 2004, 09:56 PM: Message edited by: JohnBrowning ]
THe other design uses spring tension to partial extend the tension and shoe. This ensures that the shoe is always in contact with the chain. Then once oil presure is up it increases the force that the tension puts against the chain.
If either one of these systems fail you would get one of two things. A ton of timing chain wip and clatter or it would jump a tooth.
Some systems combine all of these features. Only a moron for an engineer would depend solely on hydralic pressure to tension the chain with no provision for cold start lose of prime situation.
I suggest you go to your local parts store and check out a timeing chain tensioner. If you want one I know can be retracted with no special tools after extending it out use a 1995 Toyota Tacoma 2.7 I4. The lever to retract it is on the back side.
If you want one with no lock use 1986 4Runner it has a spring with no lock. You can push it in and out like a shock absorber. Both of the above use hydralic pressure as their primary force to provide tension.
[ May 12, 2004, 09:56 PM: Message edited by: JohnBrowning ]