anatomy of timing belt tensioner

[teigan]

i decided to change the timing belt while i had the car apart. however, i used a 4mm nail instead of a paperclip this time. the nail came shooting out once i removed the last bolt. is there a parts list or drawing of the internals? i doubt i can extract it tensioned, and i'm afraid of losing parts. it's currently precariously wedged in place by the loose timing belt. i'm gonna try and catch the flying tensioner parts in a towel. hopefully, i can retension and get a paperclip in later by using a bench vise. the gremlins seem to be out in force this week.

[wedg1e]

I use a 4mm drill bit. Clamp the tensioner body in a vice (vise to you lot ) and use a pair of water-pump pliers to compress the piston, then get the drill in quick!
If it's dropping apart on the car, as you say just catch all the bits in a cloth and reassemble on the bench. Still scary though, handling it with all that tension in the spring...

[hilly]

You may find if the tensioner has been removed a few times then a 4mm pin will not hold it all together under tension. This is because the pin locates in a groove in the tensioner piston which is only made out of plastic. After while a couple of things can happen .............

a) due the impoosble position of this thing when the engine is fitted to the car, the groove gets damaged

b) where the groove is OK, due to the plastic piston being a loose fit and only having a thin side wall (the tensioning spring fits inside it) the edge bends and the pin pops out of the groove. Hey-presto bit of expensive tesioner with loads of energy making a bid for freedom

This is what I found with mine so I made a clip from a bit of wire which fitted round one of the bolts of the tesiner bearing and the stud for the alternator. Once the tensioner assembly is put back on the engine and the belt fitted this bit of wire can be pulled off.

Here is picture of the tensioner before the belt is fitted, but with the whole thing clipped up. In the photo the clip is arrowed. Also note I have wound the tensioner screw out as far as possible to help everything stay together.




Unfortunatly when you buy a tensioner service kit the only bit you don't get is the plastic piston. I got fed up with the whole thing in the end and made a new piston out of Delrin.

Hope this helps

Andy
1981 S3


'

>> Edited by hilly on Sunday 26th February 10:53

[teigan]

thanks for the replys. i was able to get the thing recompressed and back in place. contrary to warnings in the official lotus manual, the parts didn't go flying akimbo. i also ended up not needing the vise, because the spring tension wasn't much more than your average jack in the box. i pushed the spring in from the tensioner screw side, then compressed it using the earlier removed screw behind it. checked the timing belt tension, and verified everything is to specs. i field stripped the tensioner when it was out, and there really isn't much to it. there's a spring inside a spring that butts up against the tensioner screw on one end, and the piston on the other end. the pivot joint for the idler pully has some really cheap nylon bushings that were worn on mine. i'd bet this would be the first point of failure on these units. hopefully, i can find ready replacements for next time.

[Esprit2]

[quote=hilly]Unfortunatly when you buy a tensioner service kit the only bit you don't get is the plastic piston. I got fed up with the whole thing in the end and made a new piston out of Delrin.quote]

Delrin has poor resistance to petroleum products and degrades relatively quickly. No need to run right out to the garage and replace it now, but be aware that it's life will be short compared to the factory piston. And when it fails, it will become brittle and crack/ crumble.

The OEM piston is made of Nylatron which is a brand name for a Nylon containing molybdenum di-sulfide anti-friction additive.

Regards,
Tim

[Esprit2]

teigan said:

contrary to warnings in the official lotus manual, the parts didn't go flying akimbo.

The tensioner won't go sproing just because the belt is removed without the keeper pin in place. There's a stop in the hinge and the tensioner can not open up far enough for the piston to shoot out.

However, if you remove the tension adjusting screw before releasing most of the spring tension (letting the hinge open all the way out against the stop), then it is likely that a few parts will shoot out a ways.

teigan said:

i also ended up not needing the vise, because the spring tension wasn't much more than your average jack in the box. i pushed the spring in from the tensioner screw side, then compressed it using the earlier removed screw behind it.

I vice works well. I've also gotten them back together by hand. A simple expedient is to put the tip of a large flat-blade screw driver between the tensioner roller and the crotch of the fork it's mounted in.

place the end of the fixed portion of the body against the work bench or floor, then use the screwdriver for leverage to close the hinge, forcing the piston into the bore. The piston will want to cock off axis and will need a little two-finger alignment help before it will slide in freely. Then insert the 4mm pin (drill bit shank) before releasing the pressure on the screwdriver.

teigan said:

the pivot joint for the idler pully has some really cheap nylon bushings that were worn on mine. i'd bet this would be the first point of failure on these units.

Early tensioners didn't have the plastic bushings. They're inexpensive, but not "really cheap". On the old, all metal version, the hinge would wear, the bore would get large and out of round, and the hinge would break. Or if it didn't break, at least the articulated end would cock off to one side and the belt would track off-center on the pulleys. Far enough to rub on nearby metal bits and fray badly. Left un attended, the belt could break. Whether it's the belt or the tensioner that breaks, the result is just as bad for the valves and your wallet.

The plastic bushings are a worthwhile improvement that can be retrofitted to older tensioners. Hinge life is much longer with them, and the hinge is rebuildable (replace the bushings) as long as you catch any excess wear before it starts cutting into the metal bore.

Regards,
Tim

[teigan]

thanks tim. do you have a part number and source for those bushings? mine were out of round and hence a bit mushy in perofrmance. i noticed a consequence of using the nylon was massive buildups of static electrical charge. hence the need for a ground wire; not present on early cars. this ground wire will fail of course from constant flexing with the pivot. if i were lotus, i'd have opted for ball bearings, providing longer service than the nylon and eliminating the static buildup.

[Esprit2]

teigan said:

do you have a part number and source for those bushings? mine were out of round and hence a bit mushy in perofrmance. i noticed a consequence of using the nylon was massive buildups of static electrical charge. hence the need for a ground wire; not present on early cars. this ground wire will fail of course from constant flexing with the pivot. if i were lotus, i'd have opted for ball bearings, providing longer service than the nylon and eliminating the static buildup.

Bush, Pivot, Belt Tensioner B907E1163F
Just call your favorite independent Lotus parts supplier and ask for them. No availability problem.

It's not a slip fit, so you'll need to press them into the housing. It's a low-force deal, so pliers will do it... BUT you run the risk of getting them started crooked and then messing up the entire installation. Using a vice is much better.

A ground strap is necessary and was original equipment on your car. If it's not there, then somebody omitted it at some point. Braid, Timing Belt Tensioner Earth, A082M4209F
You can make one from a piece of wire and a couple of crimp-on ring terminals. No big deal.

Actually, the ground strap was called out way back into the early 907 days even for the semi-automatic tensioners without the plastic bushings.
EF22, Earth Strap, A075M0329F. "075" indicates the 4-seat Elite.

Bushings are more appropriate for this type of pivot than ball bearings. It isn't a bad design. And plastic is actually better than metal in may ways because it's self lubricating in a place that might not otherwise get routine service attention.

The original design was not as good because the pivot bores were drilled directly into the cast housing. When the "inevitable" wear occurred, the housing was ruined and there was no factory option other than to replace it. The prevention (expectation) was frequent maintenance, which of course, Americans didn't give it. We just complained when it failed out of neglect. Adding bushings made the part serviceable/ re-useable, but it still needs to be serviced regularly.

Ball bearings are good for fast moving applications, but terrible for static applications. The tensioner hinge is basically static most of the time, but needs an ability to flex a bit and to slowly adjust to belt stretch with temperature changes or age. A ball bearing under static constant load like the tensioner would fail due to the balls bedding into the race over time (Brinelling... it happens). Bushings with their relatively large contact surface area are much better for supporting that kind of load.

The tensioner requires maintenance. The problem is that we Americans are absolutely the world's worst for maintaining anything. "What do ya mean I was supposed to change the oil... (smoking hulk in the background)." Things are supposed to last for ever, untouched, right? Wrong.

The Lotus engine requires regular maintenance, more than most. Given the vintage of your Esprit, the tensioner should have been rebuilt before now. Probably several times. If yours is "original" and is only showing the wear you describe after 20-plus years, then that indicates it's actually served very well. Above and beyond the call.

Don't wait 20 years for the next tensioner service. The tensioner is as important to the valves' good health as the timing belt. Treat it with the same level of healthy paranoia.

Regards,
Tim Engel
Lotus Owners Oftha North

[teigan]

i'll be replacing that part next timing belt change. the car has a little over 35K miles, and this is the third timing belt change. you are right that the bushings have never been changed. there is no mention of the bushing examination in the lotus service manual, so it's not just traditional american neglect to blame. it's also not mentioned in any of the online user posted timing belt instructions. [ we should add it ]
the ground wire was replaced twice before by previous owners due to breakage. when i made the latest one, i extended the length of the wire by 2 which should distribute the stress better. as for the tensioner having a static load, just looking underneath the car with the engine idling will reveal the tensioner is always making minor adjustments. through a full rotation cycle, the tension of course undulates every 120 degrees. that's a lot of flexing, which is why we get the rapid static buildup. i can't pretend to know as much about these cars as some of you, nor did i intend to when purchasing the esprit. the inherent fragility of these vehicles has forced us all to be reluctant experts.