What if your cam belt was "out by one tooth"?

[Jackonicko]

Is it possible? (It was Mr GST's suggestion, so I take it seriously).

What would the symptoms likely be?

[Specky]

Elan Scan the old girl this week and get an expert like Geoff to give the Traces the once over...

I'm sort of available...

TTFN

[theelanman]

your timing would be out most of the time and itd run like a bag o nails.....

depending on when the belt and the cam revolutions coincided....

[Rambo]

Is it possible? (It was Mr GST's suggestion, so I take it seriously).

What would the symptoms likely be?

Ask Gerald

[Jackonicko]

Rambo,

Gerald's in Australia.

And he said that it was a possible explanation for my unhappy idle and roughness at certain points on the acceleration 'curve'. I just wanted to explore a little further afore he returns.



Specky,

You're a saint! It will cost you, though. I'll absolutely insist on taking you to the Beijing D!

[theelanman]

itd run like a bag o nails.....

[Jackonicko]

Cogent, Gareth, but a little long on brevity.

Care to elucidate? Could you expand?

[Rambo]

Gerald's in Australia.

Again ? Probably spending all those ££££'s he's had from PaulP, Gary and Rip over the last few years LOL

[theelanman]

yer inlet and outlet cams...valves will be all out of sync....
they start in the correct place....however the length of the belt and the number of teeth will cause the cams and thus valves to be in the wrong place at the wrong time.....for instance if you assume your inlet valves fully closed then the exhaust valves will be open on TDC, the close by a very small ammount on the next revolution of the belt, then a bit more, then a bit more then a bit more...until it start to work in reverse..the exhaust valve opens a bit more, and again, and again..etc util you have the valves back to where they should be...basicalyy the extra tooth pushes the cams round slightly out of sync...but for instance the 100th revolution puts it all back to where it would be.....

helpful???.....probably not

[Jackonicko]

No, it was absolutely helpful. Thank you Gareth.

You mean that the valves aren't quite working when they should - meaning that the old Suck, squeeze, bang, blow cycle isn't timed as accurately and evenly as it should be.

Which would presumably screw with the idle.
Which would presumably make the timing problematic.
Which would presumably cause roughness when accelerating hard.

So how cross should I be with the person who fitted my new cambelt?

[theelanman]

not very if youd supplied the part...however if theyve done the whole thing...very very unhappy

[niall]

Why would the origin of the belt be relevant? Surely it simply needed to be fitted correctly?

[theelanman]

Why would the origin of the belt be relevant? Surely it simply needed to be fitted correctly?

coz obviously someone has bought the wrong one......
if it was jacko then its his own fault....however if its the garage then I wouldnt take my car back there again.....would you????
relevant enough???.............

[theelanman]

jon
should have been this belt...

Engine : Timing Belt
GATES Part # T169 {Automotive Timing Belt 1" x 50 3/32" (159 Teeth)}

from rock autos......or similar
cheers
g

ps if not a gates belt then the important bit is 1" wide x 50 3/32" long......and most importantly 159 Teeth

[Jackonicko]

Said Belt was supplied and fitted by a Lotus specialist who makes a big deal of only using Lotus parts, to the extent of being quite iffy about aftermarket brakes, and who only fitted non OEM rad fans to mine because OEM ones were impossible to source.

I'd be astonished if it were found to be the wrong belt..... is there any way in which it could have been mis-fitted?

Said specialist comes highly recommended, and apart from the tune/timing/overboost issues on mine has been exemplary (servicing, electric windows, exhaust, etc.).

My faith has, however, been further shaken by the way in which timing has been adjusted on subsequent visits - without a timing light, without being hooked up to a Tech 1, simply by adjusting the CAS on its bracket.

[Specky]

we'll have a look some later this week...

I'll pop the top cover and see which belt you have fitted...

Calm down....

TTFN

[Jackonicko]

Thanks Specky,

I'll look forward to it. (And to the black magic art of Elan-scanning it). Just let me know when's good for you, and whether at the Swindon or Benson end.

I'm actually fairly calm, and I'm really very pleased that I might at last be on top of the niggling series of problems that have dented (not prevented!) my enjoyment of the car. It's all small-scale emotions, because despite the problems, driving it is still a pleasure, and the reaction one gets from others is so often heart-warming, and it has been a passport to a great community, and to meeting some very, very solidly good people. The thought of having all of this and a car which idles happily, and runs as smoothly as it did 'pre-belt' (but without the overboost) is a really exciting one.

[Specky]

Your end of the world...

I'll be in touch...

TTFN

[Enright]

While I don't disagree with Gareth about the engine running like a bag o nails, I've got a slight issue with the "length of belt" description.
As long as there's enough adjustment in the tensioner to keep the belt as tight as it should be, then it makes no difference if it's 5" or 5 miles long!
If it's one tooth out, it will always be one tooth out. The important bit is that the camshaft pulleys are ALWAYS twice the size of the crankshaft pulley.
It still needs to be checked and corrected, but unless the tensioner is allowing the belt to slip then it shouldn't get any worse.
As the CAS runs off the exhaust camshaft, if you can apparently time the engine up properly and get good compression readings, then my suspicion would be that either the inlet camshaft is out of sync, that the CAS itself is on it's way out, or that it's coil packs.

[Jackonicko]

It's not getting worse.

The Coil packs have been done.


Specky,

Another meet at the Cafe? I hope you're hungry! I don't do bacon and eggs alone.