Greenlight

I think that there are several factors that must be considered.

1) As Billman stated, some oil is bleeding off due to clearances between the valve piston and the piston bore. Thicker (or fresher) oil will reduce the bleed off on a worn assembly. In other cases, the tolerance stack up of components may contribute to this problem.

2) The amount of slack/wear in the timing chain. As the piston is required to extend (due to timing chain wear or, in the case where a cylinder head has been milled or a thinner head gasket it used) the spring tension is reduced. The reduced spring tension allows for a reduced ability to control the timing chain "whip" on the slack side of the chain.

After reading posts on this subject for several years, it appears that the people who experience this problem the most are the ones who "hot rod" them the most. These vehicles will likely have the most timing chain wear/stretch and even multiple chian tensioner replacements do not solve the problem. Does anyone else agree with this?

I would like someone (read Billman) to measure the amount that the piston is extended in a noisy tensioner and measure the amount of piston extention in a car that has never exhibited a tensioner noise. Then, remove the main piston spring and measure the spring force at that particular spring length.

This can be done by removing the allen head screw on the cylinder head that is used to "pull the pin" and making a mark on the piston prior to removing the tensioner.

Billman, BTW, several monhts ago I asked about purchasing one of the used tensioner assemblies from you so I could use it on a spare engine that I'm building. Is that offer still available? I'm almost finished with the new engine and will need a tensioner within the next few weeks. Thanks.

fperra

For a linear rated spring, which this spring is, as long as it is compressed, the force it exerts will remain the same. In other words, if it is less compressed by 1/16th of an inch because of wear, it will still exert the same force on the chain as long as it is still compressed. Basic spring mechanics.

My thinking says the problem lies with that threaded mechanism that sits inside the cylinder that pushes on the chain.

Slows2k

I've replaced tensioners on high and low milage cars, all AP1's (but some AP2's are noisey) some of the cars are driven hard. Some are granny owned.

RED MX5

I'm sure higher revs, more often, do lead to more timing chain wear, but given the way I drive, and the fact that I haven't had a TCT problem yet, I don't think it's related to hard driving. If it was I'd surely have had a problem by now.

I thought the tension was determined by oil pressure rather than the spring.

mxt_77

That's not right, is it? Linear Springs are rated at a certain amount of force per distance, like kg/mm, right? So, if it's rated at 1kg/mm and you compress it 1mm, then you get 1kg of force. If it's compressed 2mm, then you get 2kg of force. So, the more it's compressed, the more force you get.

Not sure how the hydraulic factor of the tensioner comes into play, though.


Just another reason to go FI and put on a thicker head gasket.

RED MX5

Yea, springs are rated in terms of force/distance, like 400 lbs/in. In such a case, one inch of deflection requires 400 lbs and two inches would take 800 lbs. It's the rate of increase that is linear, not the rate itself.

RED MX5

Bill, is it the spring or the oil pressure that actually supplies the tensioning force?

jasonjm

And oil thickness/temperature.

No?

Maybe the guy was running some 20W50 hehe

Or maybe his engine was all sludged up?

fperra

After rereading my post, I didn't do too well in the explanation. The big spring is approximately a 6 lb/inch spring from by measurement. Assuming it is compressed 1 inch during normal operations, it is exerting 6 lbs of force on the chain. If the chain streches and relieves the spring by 1/8 inch, it is now only applying 5.25 lbs. Not much of a difference.

In any case, it seems to me that this weak of a spring is not the main force that is applying tension to the chain. Measuring the small spring, it is more on the order of 10 lb/inch. But its purpose appears to be to allow the threaded thingy inside the cylinder to take up slack in the chain, but not to exert force on the chain. So, that leads me to believe that oil pressure is the source of the force. Maybe Billman is right in suspecting the small check valve on the front of the housing. Or maybe those cars that are having this problem have low oil pressure at low rpm's. Not low enough to cause engine damage, but not enough pressure for the chain tensioner to work.

Greenlight

O.K., I've wanted to do this for some time, but I guess I've been too lazy.

I measured the one tensioner that I have and performed some basic calculations.

Piston Diameter - 0.628" ...... Area - 0.30975 in^2
Housing Bore - 0.631" ...... Area - 0.3127 in^2

Delta Area (housing minus piston) - 0.00297 in^2 ...... Equiv. Dia. - 0.0614"

Oil Inlet Orifice Dia. - 0.090" ...... Area - 0.00636 in^2
Oil Bleed Orifice Dia. - 0.030" ..... Area - 0.000707 in^2

Effective Area (Inlet oil minus outlet oil) - 0.002682 in^2 ..... Equiv. Dia. - 0.058"

This means that you have an effective hole 0.058" in dia. orifice feeding the oil to the tensioner.

Idle oil pressure (service manual) 36 psi @ 176 F

Force on tensioner due to oil pressure @ idle - 36 psi x 0.3097 in^2 = 11.15 lbs. (w/ no pressure loss due to leakage)

Force on tensioner @ 85 psi - 85 x .3097 = 26.3 lbs.

Spring force:
Note: My spring has been stretched a little, so this value may not be the same as a stock unmodified spring. I marked the piston position before removing the assembly, then measured the spring force with the spring at the appropiate length.

6.3 lbs.

After taking several measurements the spring constant "k" was calculated as 4.42 lbs. per inch (remember F = k x from physics).

Total force of piston on the tensioner 11.15 + 6.3 = 17.45 lbs.

If the head is cut 0.050" the slack in the chain will increase by ~1/2" (hard to believe, but take a piece of string and test it for yourself).

The spring force will be reduced by 4.42 lb/in x .5 in. = 2.2 lbs.

This is a 13% reduction is total tensioner force and a 35% reduction in the force on the tensioner caused by the spring (at idle).

Some other things to consider:

1) This estimation assumed that the "leakage" did not reduce the oil pressure at the piston.

2) This estimation assumes that the piston "bind" in the bore (if any) has no effect on the apply force.

3) This estimate assumes no leakage by the two o-rings that seal the apply oil.


Everyone can draw their own conclusion from this basic analysis. I've only presented this as an informational component for further analysis and discussion.