Valve seat wear and Optimax

[Tim Falce]

My engine (4.2 Jaguar) ran all last season without a problem. This year, although I have only done 2 races with 2 dnf's, it has been a bugger to start. I have had to rebuild it due to bearing failure and it hasn't run since May or June. When I came to start it the other day, it wouldn't go and after a bit of investigation I found it had absolutely no compression on 3 cylinders. This was due to the valve clearances closing right up so the valves weren't closing properly. After 2 days of re-shimming it is now OK.
So why could this have happened? I haven't touched the head so there has been no changes by me on that side. The only thing I can put this down to is some serious valve seat wear. I ran the car on Shell Optimax all last year and the valve seats are supposed to be hardened for unleaded (1984 head) reconditioned 3 years ago by so called professionals.
So any theories as to why this may have happened and so quickly, could it be the petrol?
BTW the engine wasn't run all last winter although it was stored in the garage.

[graham bahr]

i ran my beemer on optimax without an additive on seats that were not supposed to be hard enough for unleaded fuel without problems for many seasons dipite reving the thing to 8K and never had a problem, in any case seat resession happens slowly not suddenly.

i have come across this when seats have been fitted but didn't go fully home, until halfway through a race season.

its also possible although less likely that your valves have stretched, although that normally only happens with old high mileage two piece valves.

you didn't get the jag bits mixed up with briggs and stratton bits did you?

[Tim Falce]

Originally Posted by graham bahr

you didn't get the jag bits mixed up with briggs and stratton bits did you?

No, that just smokes like a Jag

[Al Weyman]

It is more likely to be that everything has settled down and bedded in, collets locked in to the retainers, valve seats bedded in etc. I used to service old jags years ago and shiming clearances was a pain for sure. I always give the end of the valve stems a good whack several times with a mallet to make sure they were sitting down snug, not very scientific but works as any minute bit of crap can cause them not to sit down and give you a dodgy reading.

Ain't hydralic tappets a wonderful thing.

[zefarelly]

I didn't even fit hardened valve seats to my head this year, I figured the life is so short between checks its not an issue, and with big valves theres no point in taking the risk of them falling out!

the one thing I always do however , is start the engine regularly . . . . .make sure nothing gets the chance to settle too comfortably

[graham bahr]

Originally Posted by Al Weyman

Ain't hydralic tappets a wonderful thing.

err no, they are a pain in the preverbial,

i've got an alfa engine in the garage with a load of bent valves due to them pumping themselves up, they can also be a real pain when timing up cams.

me i'd go for bucket and shim every time, almost set and forget, tim must need more practise with shims it shouldn't take two days to sort.

Al i would tend to go along with your thoughts on tims clearances, infact when i build a new engine i always set the clearances 2 thou big to allow for some bedding in, and if things dont bed in and close the gaps up, well thats no prob i dont know of any engine that wont run happily and quietly the the gaps such a small amount on the large side

[graham bahr]

Originally Posted by zefarelly

I didn't even fit hardened valve seats to my head this year, I figured the life is so short between checks its not an issue, and with big valves theres no point in taking the risk of them falling out!

quite! and it has the bonus of being cheap!

[Tim Falce]

Originally Posted by graham bahr

err no, they are a pain in the preverbial,

i've got an alfa engine in the garage with a load of bent valves due to them pumping themselves up, they can also be a real pain when timing up cams.

me i'd go for bucket and shim every time, almost set and forget, tim must need more practise with shims it shouldn't take two days to sort.

Al i would tend to go along with your thoughts on tims clearances, infact when i build a new engine i always set the clearances 2 thou big to allow for some bedding in, and if things dont bed in and close the gaps up, well thats no prob i dont know of any engine that wont run happily and quietly the the gaps such a small amount on the large side

Agreed on the hydraulic tappets, I've had no end of problems in the past with them.
As for practise shimming the head, that's the first time I have ever attempted it. I didn't have any spare shims and it was a matter of swapping some round until I got the correct clearances and machining down the oversize ones.
I am now worried that the valve seats may have come loose and moved, is that possible or likely?

[graham bahr]

Originally Posted by falcemob

I am now worried that the valve seats may have come loose and moved, is that possible or likely?

does the engine have the origonal jag ones? if it does its unlikely they have moved, unless the head has been seriously overheated in which case they will try and fall out, and you'd soon know if they did.

if the engine has had replacement seats fitted its a bit more likely that they could have settled further in the head, if they hadn't quite gone fully home when first installed. how much too tight were the clearances? and how many valves had a significantly tight clearance?

[Tim Falce]

Graham there were about 4 valves affected, 3 inlet and 1 exhaust. The worst was 16 thou out. The others were not as bad but still leaving the valves slightly open. The engine is a rebuilt one and more than likely had new seats but I am not 100% sure. The engine was seriously overheated earlier this year but the starting problem was happening before that. If the seats had tried to fall out then the gaps would be bigger not smaller.
Will wait and see if I still have an engine next Monday. If not I will have to talk nicely to my aged uncle to see how busy he is this winter

[zefarelly]

I've never actualy had a problem with loose seats, the more likely problem for me is hitting the water jacket when fittingthem, or leaving so little meat between them that the head cracks.

Until I find an aluminium head I'll stay as I am !

[Eric Falce]

I'm not so botherd about valve clearances,valve seats or what as long as Tim has got(as his fav aunt would say) his happy head on this weekend.

[ian_w]

You can get significant inlet valve seat wear if you run without an air filter. Its not worth the risk of running without a filter, there is no performance benefit to be gained - you don't see F1 engines without air filters.

As regards Grahams tip of shimming a little on the large size - you need to be cautious here, the valve clearance values specified by the cam designer are not arbitarily set.

The opening and closing portions of the camshaft are called the 'ramps' these are very gentle and designed to take up the valve clearance and make sure the valve is in contact with the cam before the cam whacks the valve open and also insures that the valve returns gently back onto its seat. If the clearance is too large the valvegear will make a fearsome clattering noise as the cam hits the valve during opening and of more concern is that the valve will be dropped back onto its seat very violently - its is quite possible to crack the valves if you do this. I have experience of a valve cracking issue on a race engine that was fixed with a 2 thou reduction in tappet clearance!

[Tim Falce]

Originally Posted by ecktic

I'm not so botherd about valve clearances,valve seats or what as long as Tim has got(as his fav aunt would say) his happy head on this weekend.