Valve clearances.....

[glynherron]

Hi guys again..........

So while we're almost all in very small pieces, I've checked the valve clearances.

These are my findings

Exhaust spec

0.010" to 0.012"

0.011

0.012

0.011

0.010

0.012

0.013

0.012

0.012

Inlet spec 0.005" to 0.007"

0.008

0.008

0.010

0.011

0.015

0.008

0.008

0.008

Question: as valves and valve seats wear I would expect the clearances to decrease. But just about all except 1 are on the max clearance or greater.

Exhaust no 4 is the only worry to me, being on the minimum. I guess inlet number 5 will be a little noisier?

Again, comments please.

Thanks

Glyn

Edited June 21, 2011 by glynherron

[andydclements]

Valves and seats wear tightening clearance as yu sate but also you get wear on the top of the valve stems and the shims themselves wear at the point they meet the valve stems, ther's also potential for the lobes of the cam to wear (but miute amounts).

It's not unusual to remove a shim and find a visible recess in the centre of one face where the valve stem has warn it away despite both being hardened material. I've never bothered to measure the differenc ebetween outer edge and inner area but I'd gues I've seen some shims with the best part of .2mm gone. I'd go and check some of now if I could but my neighbour hasn't found my box of 200 shims yet (I trust him that he will, he just doesn't know where they are at present).

Yes, I'd say inlet no 5 would be a little noisey, but the others aren't too far behind. they will cost you a little power as the inlet valves will not be open quite as long as they shouold and not quite as far as they should.

[glynherron]

So how if clearances decrease with time, can the clearances be larger than the max spec?

The obvious answer is that whoever did the last work on the top end didn't have enough shim sizes and left them on the large size?

Can you think of any other explanation

ps I'm using clean Bluepoint feeler gauges and no other tat

Glyn

pps good luck with your neighbor finding the shims!!

[Jonathan]

Just done this job on mine.

Specs were :

Valves back>front 1/1000" (exhaust 11/9 8/13 12/12 11/11) (inlet 6/6 6/7.5 6.5/6 6.5/6.5) Tollerance = 10-12 Exhuast, 5-7 Inlet

Mine is and always has been a bit tinkly and I assume this is the 9''' and 8''' under tollerance. I was gonna have the tower off this time but considering my mileage I thought I'd skip it (right or wrongly)

Over tollerance....I thought that'd be a bad thing cus the valve would not have time to operate correctly esp at high rpm. Nor would it follow the cam profile correctly - depends on how far you wanna take it out of spec.

[glynherron]

But would under tolerance lead to potentially zero clearance when hot, and excessive valve temperatures?

I think that over tolerance is better than under, although none it ideal??

Comments please!

Glyn

[Jonathan]

The tollerance is an optimal window, there really is only 1 right answer.

Either way, above or under the valve is gonna follow a different profile than intended.

Having said that mine clearly has issues on the exhaust (clearly mine were not checked past C service which is why I do it all myself).

I could have done mine this time around, but I wanted the car back and running - I'll probably sort it later as I dont think I'll get that many miles in the mean time.

I'd say if you're gonna set the things up go for upper tollerance, so 12 and 7 thou

[DanR]

Old tuner's rule of thumb: Tight for torque and loose for top end.

[andydclements]

and the determination of whether the clearances tighten or loosen when hot takes this into account

the head i ali and gets quite hot but is cooled directly (water and oil), so it expands moe for its given temperature than steel.

The valves are steel and get very hot (main face in in the combustion chamber) they are cooled indirectly (heat transfers to head which is cooled, plus there;s the air coming in that cools the inlet side a bit, so expands less for the given temp but gets hotter than the head.

valve seats- minimal materal so expansin should be minimal, ditto cams themselves and followe rbuckets and shims.

If you try and take that all into account you end up with a nightmare of calcs, hence Lotus spceify it when cold and we have to assume they made sure it was all good when being designed. As Jonatan said, spec is optimal and as long as it's in the window it's fine. ideally aim for the middle of the window but don't worry if it's in the woindow.

[glynherron]

So is the concensus of opinions to take off the cam towers and re-shim?

I'm now thinking of removing the head too and relapping in the valves etc while I'm at it.

Any idea as to the cost of the parts required eg gaskets, shims to do this work from where I am now?

I need another job..........

Glyn

[Jonathan]

I think it's def worth doing both, the inlet is well out so youi might as well get them both in, in for a penny in for a pound.

I really struggled with whether to do mine, cash is very tight atm and I really just wanted the car back on the road for the small mileage I will likely do - next opportunity I will definatly re-shim.

This is what winds me up though about C services and some garages - they say the clearances were done but me not being a complete mug do you reakon that 2 of my valves have dropped 2-3 thou over 3,000 miles.... ?

At least DIYing it you can have a record of whats done and KNOW it has been done and done propperly.

[Mike6]

Interesting comments about valve clearances. One of my cam carriers has gone and cam has damaged top of valve. So head off time but I checked inlet clearances and could find no clearance at all on most of them. Not even sure valves were closing properly. Purchased a set of thinner feeler guages and just about managed 0.009mm.

How can they be so out - suspect a bodged job as all shims are identical thickness which would not be logical. Its a difficult job to get right and takes time. I guess no garage is going to do the job properly when they can cut corners - not as if its visible when you get the car back.

Logic tells me that clearances will increase with usage (valves are hardly likely to stretch themselves) so this must be an area where corner cutting is taking place.

[andydclements]

Yep Mike I'd suspect a bodge job as well, it's very unlikely that they bought a set of shims and then had the valve stems ground to suit the shims.

[lotus4s]

Logic tells me that clearances will increase with usage (valves are hardly likely to stretch themselves) so this must be an area where corner cutting is taking place.

Actually, the opposite is true. The valve clearances get tighter over time as the valve continually hammers into the seat. It's best to shim to the higher limit of the spec as they will close up over time. Generally, the only time the valve clearances open up is if there is a build-up of some kind not allowing the valves to fully close.

Edited June 23, 2011 by lotus4s

[Mike6]

But surely if the valve hammers into the seat it is going to wear away material making the gap at the cam greater rather than smaller. However I am probably wrong

[glynherron]

As the valve seat wears, the valve is allowed to go further into the cylinder head. The camshaft is fixed, so the valve gets closer to the camshaft, so the clearance decreases....

[mc21.8]

Just do the inlets

[Rich H]

A noisy tappet is a happy tappet!

As above larger gaps are 'safe' as smaller gaps will result in the gap closing up when hot and potentially holding the valves open and loss of compression/burned valves adn so on.

I need to do mine at some point...

[Mike6]

Rich

I reckon that was a problem on my car. Shattered exhaust cam follower started me off but took compression test before strip down and couldnt get any reading on any bores. Then discovered nil clearances on inlet valvest which must have meant that on hot engine valves would not have closed properly. One thing lead to another and I now have pistons and liners out.

What I am finding hard to grasp is that the top compression rings are so thin they can the slid up and down the bore without having to be squeezed together. I keep having to go back and look at the rings - the wear is unbelievable.

[Rich H]

Bloody hell!

[glynherron]

Mike, how many miles has your engine done?

[Mike6]

Purchased the car as a project with no service history or mileage. Understood to have been serviced regularly and maintained by Bell & Colville but then stood up for a number of years (1 owner car).

Managed to run the car for a couple of years but wondered why it was so slow and difficult to start. A significant amount of the coating on one liner has gone but the top comperession ring on each cylinder has worn to a very small band. Luckily the crankshaft looks ok with some wear to the shells but no scoring etc. Unfortunately dismantled in situ so cannot get crankshaft out.

Dave (CHANGES) is helping me out with parts and advice so thank goodness for such nice enthusiasts.

[andydclements]

Well, having paid circa £200 for a few hundred assorted shims I went and did SimonF's Engine shimming job (I have swapped his old ones of the incorrect sizes with mine of the correct sizes), I came home and for once thought I'd better put them somewhere safe so that I do not knock the off the shelf and end up loosing several. I found a suitable location, moved a few things and picked up the biscuit tin that has cable ties in. I then swore for a while but not due to knocking the shims onto the floor. I found the box of Hesketh motorcycle shims that I thought I'd loaned out and had lost trace of. At least I should have enough of any given size.