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TDC flywheel marking

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post-1321-0-95728100-1365978776.jpgS3 turbo LC

I am confused about the correct position of the TDC marking in the flywheel inspection hole.

I understand it should line up with the metal pointer on the right hand side of the window at TDC.

I have aligned the cam sprocket dots and the flywheel TDC does not seem to line up with the metal pointer.

When I set my strobe to 12 BTDC and run the engine at idle the TDC is pointing to the marker perfectly. Car runs moderately well at the moment.

Am I missing something, maybe the flywheel TDC marking is not meant to line up at static TDC ?!

Or my cambelt has slipped.  Picture attached.

 

 

 

 

 

Edited by robc

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Go at it the other way and let us know what you find. With the flywheel marker aligned at TDC where are the dots on the cam sprockets?

Flywheel markings are absolute so should be in line with the marker at TDC whatever the engine sped.

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Since the camshafts run at half engine speed, trying to check the alignment by working from cam to flywheel is liable to error. As Andy says...set the flywheel to TDC, then check the cam dots. It is unlikely that they will align perfectly, but they should be very close to alignment...remember the only adjustment is one tooth either way on the cambelt, so you can't get perfect accuracy. A small fraction of error wil make no appreciable difference to performance; but you can get vernier cam pulleys so that each cam can be set exactly to the correct setting. With a rubber band driving them and spring loaded tension adjustment, there is bound to be a fair amount of wobbling about whilst the car is being driven!

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Now that there's an image showing it's fairly simply, that's circa 5 degrees out, possibly one tooth on a cam sprocket so I'd say either it has slipped since belt was fitted or error when fitting.

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I love this forum, thanks Andy and John.

I will do as you suggest and line up TDC on flywheel and picture the cam dots to see if its a cam belt slip.

I didn't fit the belt, a lotus specialist did.  It could have slipped a tooth whilst running - is this common ?

I have had various performance issues over the last 2 years, so its difficult to say if I would have noticed a belt slip.

I presume the associated power loss is very noticeable?

thanks again chaps.  I will post a picture when I next get near the car next weekend.

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Cambelts do slip, and the first symptom is power loss. I know this to my cost.....I didn't think of the possibility and then the arrangement slipped more teeth and ate the inlet valves. Anytime you get a loss of power, first thing to do is to check the cam timing...set the flywheel to TDC on the firing stroke for no.1 and have a very good look at the cam dots.....(!) Snubber settings are quite critical, I think, as well as tension. Sadly, it was only after the disaster that I thought of cam timing.....

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Agree, my money would be on cam pulleys being out, rather than the flywheel.

 

While rebuilding my engine, I wanted to make sure engine TDC markers were accurate, so I carried out a 'true TDC' check.

 

They were almost bang on- only 0.5 of a degree out.

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A local TE owner (Simon) had a belt slip only a few days after we'd fitted it, and I know we'd tensioned it correctly. It only takes a small amount of excess resistance to rotation and the semi-auto tensioner lets enough movement in the belt for it to slip. We're now moving it to a fixed / manual tensioner of the later cars. 

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Loosely related:  wookie and I were working on a dry sump engine (removed) some time ago.  The belt had very recently been changed (not by us, I hasten to add).  I'd reinstalled the head and towers and was refitting the belt.  With crank pulley at TDC I checked the cams. "Perfect" I said.  Chris was at the other end and disagreed.  The flywheel was about 7 or 8 degrees out.

 

After a few minutes of disbelief and head-scratching, we removed the crank pulley, to find the woodruff key mashed.  It looked like the pulley had been hammered into place, maybe by a vicious power tool, and had offset clockwise several degrees.  Nasty.  Naturally this kicked the valve timing out.

 

Prior to this I'd always taken a keyed crank pulley as an absolute reference.  Nowadays I double-check the flywheel too...

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Hi Chaps,

I lined up TDC on flywheel exactly this morning.  I then took a picture (attached) of the cam sprockets.

one tooth out I think - your thoughts?

post-1321-0-62023200-1366471314.jpg

  • Like 1

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I think you're probably right, it may be one tooth on one or may be one tooth on both, it depends because you need to compare to the absolute line from the centres of the shafts, in that respect you're better off doing it on the other side of the engine where you can put a decent straight edge in to compare to.

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Definitely out if crank is at TDC.  I'd come at it from the other direction: Line the cam dots up perfectly, then see how far out the crank is.  I reckon one tooth on the sprocket.

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Is this photo taken from the gearbox end looking forward? Should the phot not be taken from the other side of the cam sprockets where they are timed from?

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Mine's the same both sides, and it's a jolly sight easier to work from the gearbox side! There's definitely a cam timing error in the photo; I agree with Gary, probably one tooth out on the crank sprocket. I'd loosen the tensioner, slide the belt off, set the pulleys correctly and slide the belt back on again. Remember that the belt should be tight from the crankshaft pulley to the exhaust cam, the exhaust cam to the inlet cam and the inlet cam to the auxiliary pulley. Make sure the ignition timing is correct, too....once those three lengths are nicely tight and all aligned, then the tensioner takes up the slack from the auxiliary pulley to the crankshaft. It's all too easy to make an error by not getting the right bits taut...that gives the sort of error you show. Once you have it correctly positioned, turn the engine over manually at least twice and recheck the alignment. Set the tension properly and make sure the snubbers are aligned and the clearances are correct!

Edited by molemot

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Thank you all, excellent advice.  Would anyone guess what kind of performance loss this would cause?

I have been chasing performance issues on this car for many months, done many things carb rebuild and re balance, plugs leads cap etc, but stupidly not checked the flywheel TDC until now !

Its due a cam belt so I think I will replace and service the tensioner at same time.

 

I read someone suggested fitting a superior later tensioner than the standard fitted.  Any advice?

Also not done a belt on this car yet myself, Krikit, Borroughs or frequency/Hz tuning ?

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I had a belt out by a couple of teeth, it ran  but was lumpy on idle and lacked the usual grunt, getting better (more even) as it got to higher engine speeds but still missing a fair bit of power.

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mine is lumpy on idle, and flat with a bit of excitement as the turbo cuts in.

I spoke to an experienced engineer this pm, he was surprised that the belts slip.

Sounds like from what Molemot suggests its poor tensioner setup that makes the belts slip.

I would still love advice on what tensioner technique people advise.  Krikit, Burroughs or the frequency tuning technique.

 

thanks to all for the advice given.

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Frankly, I'm more inclined to believe that many belts are incorrectly fitted, rather than slip.

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I didn't think it was possible for the belt to slip until it happened to me!! I was driving back from the continent, the beast was going nicely....got to Dover and, on the trip back from there to Staines, I noticed a distinct loss of power. After I had finished the journey I tried to find out why...never thought of valve timing, that had been set up precisely and the belts don't slip, right?(!) I swapped coils....checked carburettion...fuel delivery....couldn't see anything. Would rev OK with no load, but when driving it wouldn't pull the skin off the proverbial dessert. In the end, in total frustration, I must have revved it too much or got a load reversal on the belt by being stupidly ham fisted, and the thing came to a sudden halt. Compression testing revealed that there wasn't any in any cylinder, so I finally checked the valve timing and found that the inlet cam had slipped on the belt. Then she went on a trailer back to the workshop at Mole End and a new set of inlet valves went in...etc.etc.etc.!!

After this, the first thing I recommend if anyone has a power loss is to check the valve timing....it being easy and free to do, and disasterous if allowed to continue in a duff state.

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I reckon mine has been in this state since my last big service, since then I started to notice lumpyness at low revs and flat performance.  This was 2 years ago (! silly me), over which time I have done so much to try and correct my performance issues: rebuilt carbs and balance, fuel pressure delivery check on the road, air leak search, ignition timing (only at flywheel !) and leads plugs arm etc, compression checks etc etc.  I have even shown the car to another 'specialist' who said the car is very good but a bit lumpy on low revs needs a tune + he left my bonnet unlatched (strange man).

 

Don't worry I wont drive the car again, although I have driven it like this for hundreds of miles. I need to change the belt anyway.

 

What a great forum. I love it.

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Hi,

 

A foto of my engine when I did the cambeltchange myself (engine out)

It might be usefull ?

 

distributieriem.jpg

 

Geert

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The reason Lotus changed from using the earlier trapezoidal toothed belts to the later semi-circular toothed belts was because of belt slippage, very prevalent when starting on cold, frosty mornings. A well charged battery & a loosely tensioned belt can slip when the starter motor starts to spin a cold engine with thick, viscous oil. Also bump starting can cause the belt to slip if the clutch is engaged too quickly.

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I recall reading that when the first Esprits were shipped to America, they were sent by rail across to Seattle (iirc). These early engines didn't have any spring loading on the cam belt tensioner...and it was the dead of winter...so everything got cold soaked in transit. When they tried to start up the cars to drive them off the train, the engines had contracted sufficiently for the belts to be loose enough to come off!! Thus needing a full set of new engines to be shipped out.... 

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Thanks Geert, useful picture.

 

i have an oil leak on cam covers and a rear centre sump bolt (which i believe goes into an oil well).

The belt is extremely dry and no signs of oil at all.  So i firmly believe oil has not caused the slip.

However i think its time to extract lump and do the honest thing and sort these things out.

 

Although the passion in me says lets just try changing the belt and realign the cams.

I changed the water pump with engine in place which wasnt fun.

 

Changing belt in place. tell me more ..

position TDC, tensioner off and service, crank pully off. and then set tension as Molemot described no slack on belt path apart from where the tensioner is.

 

what cam belt tensioner techniques do people recommend.  I have heard a frequency tuner is an extremely accurate way to do it and easy for me to do.

i dont have a Krikit or a borroughs gauge.

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Hi,

 

A foto of my engine when I did the cambeltchange myself (engine out)

It might be usefull ?

 

distributieriem.jpg

 

Geert

Hi Geert,

 

Out of curiosity do you have a single 'v' crank pulley, or double?  mine is a single 'v' with the belt going to alternator and water pump but looking at the parts catalogue I can't see a reference to a single 'v' pulley at all, only double 'v' and triple... As I'm trying to add an aircon compressor it will be important. 

 

Also All, what do you think about the crank pulley mark?  I'm about to do my belt, I've lined up the dots and the flywheel has a blob of paint in the right spot (I didn't look closely enough for a TDC mark but will do that tomorrow), but the crank pully mark is nowhere... the guide there has timing marks of -20 and -10 but none for 0. 

 

Is there an easy way to tell if I'm at TDC for cylinder 1 (apart from the obvious of putting something down the spark plug hole?

 

cheers

Simon

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