Standard Valves In Big Valve Head !!

[Lotus fan]

Took my big valve head to a local recommended machine shop to have new seats, guides and valves inserted (because I couldn't do it myself - heating head etc.).

Anyway, I got the head back all nice and clean and with a 0.001 skim.
While I was putting new valve springs into the head I decided to measure a new inlet valve that the machine shop put in.
Aaaarrrrggghhhh........ they had put in standard valves and not the big valve ones !!!!!

The ID of the seat is flush with the port so nothing will impead the air/fuel mixture.

I have read Miles Wilkins book re: the Super S/E and also these threads........
elan-plus-f13/sprint-cams-t18318.html
elan-f15/reprofiled-camshafts-opinions-t23688.html

So in essence I do have a Super S/E

D type cams
10.3 : 1 Compression ratio
Suitably jetted DHLA 40 Dellortos
Standard !!!! inlet valves

So really is it worth demanding that the machine shop put the 'proper' valves and seats in
or would the increase in BHP be so negligible that its not really worth getting annoyed about.

The engine will NOT be raced.

Some of my fellow CLOG's think it should be ok.
http://autos.groups.yahoo.com/group/che ... nersgroup/

Sorry for the rant.

Ian F.

[trw99]

Ian

I don't think you would notice any difference in day to day driving, to be honest, especially with well tuned Dellortos.

Tim

[AHM]

Ian,

Technically you can discuss on way or the other.

I think that you should ask yourself if you will be happy, or if it is going to bother you for years.

Personally I would make a polite call to the machine shop to discuss. Valves are easy to change and the same price, seats may be able to be machined in situ or changed. If there is any work involved you will have a sensible conversation about who pays and how much, you might find that they say whoops sorry sir bring it in and we will change them right away. If they had the old valves and seats they could have checked. I wouldn't demand anything until you have had a sensible discussion!

But if you don't ask you won't know, and it will niggle you!

Simon

[gjz30075]

If you asked for, and PAID for, big valves, then by all means call the shop to make them make it right. However, you probably won't be able to tell a difference. I have standard valves in my 150hp, 1720 cc motor and was told, before it was built, it's not worth the effort and cost to fit them.

Greg Z

[bcmc33]

The Big Valve engine was bullsh*t anyway. As long as you had the head ported to some degree - that will make the difference you're probably look for to make the performance meet the published figures.

[AHM]

Some of the best brains in engine design at the time went to the trouble and expense of testing larger valves, got more horsepower, and it is dismissed at BS?

Another, David Vizard, says on the subject "The head in its standard form is very efficient. If any modifying is contemplated it must be done with perfection to realise a worthwhile gain".

[Andy8421]

Miles Wilkins' twin cam book mentions that the inlet port throat on the big valve head was opened up using a different form tool to the standard valve head.

If so, it seems surprising that a standard valve insert could be fitted to a big valve head with "the ID of the seat flush with the ports"

It may seem a daft question, but you are sure it was a big valve head to start with?

[elan_fan]

It doesn't really matter what valves you have got in your head, it's the port size that they sit in that maters. That is where the extra flow comes from. If say you had Lotus big valves in a big valve port (which are only something like 60 thou bigger) and a head with the same port size and standard valves which have been gas flowed and a proper radius on the valve seat with a perfect 30 thou seat that is right on the outside edge of the valve the gains would be quite significant over the standard big valve head. There is quite a bit to go on the ports to even maximise a standard size valve setup. How far has the machine shop gone with your head in terms of preparation.

I think that in your case you need to go back to them and show them their mistake and put it right/have it put right for you own peace of mind. You will be annoyed with the whole big valve engine with small valves. In terms of real world performance I suspect that given the way that most machine shops build engines you will gain very little to nothing from the swap.

regards
Mark

[alan.barker]

i think the most important is if the valve seats were fitted correctly. big valve or small, i don't think it matters
Alan B

[elansprint71]

Is the O/D of the "Big-valve" seat the same O/D as the normal valve seat? I would have thought it was larger but what do I know?

[UAB807F]

I know you could get oversize O/D inserts for cases where the head was damaged getting the old guides out but otherwise I thought the seats were the same for both std & big valve heads. Way back in the 70s I bought some 1.6 inlet valves from Paul Ivy as he said that was pretty much the largest valve you could fit without going to oversized seats. 1.62" comes to mind for some reason but I can't remember if that was the valve diameter or the seat O/D. To fit the 1.6's all I did was to cut a new surface & relieve the bore to smooth the flow which is basically what Paul said he did, so I'd guess they are the seats are more or less the same in both std & sprint heads. (mine was std)

Getting back on topic, I think if I had the head sitting on the bench then I'd swap the valves because it's easy to do and only minimal cost. If the engine was assembled & in the car, then I wouldn't bother because although I'd know the valves weren't "right" I doubt I'd ever tell the difference in practice. As to how much difference the larger valves make, I'm sure I remember an article in Club Lotus which said most of the gain was from the new cams, higher C/R & re-jetted webers with larger valves being a minor contributor but the valves made for better marketing hype; does "Big Valve" sound better than "Different Cams".....

Brian

[Lotus fan]

Thanks for the replies guys.
Andy8421 - It is a Big valve head with an 'N' next to spark plug 1.

I'm going to speak to the machine shop tomorrow just to tell them what they've done.
It seems that the general consensus is to leave it as it is because I've got the D cams and Dellortos.

The funny thing is - the person who I bought the car off in '97 had the car religiously serviced every 3000 miles
at Miles Wilkins' garage !! He had the car from 1982-1997 and spent 21 grand on it !! ?864 of that 6 months before he sold it to me
I probably would have taken the head to Miles if he was about 200 miles closer.

[Lotus fan]

Ok, spoke to the guy in the machine shop.

His reply was simple and concise.
Because the head in his opinion/experience had previously had 'a big skim' he didn't want to put in big valves
and then for me to have valve to piston contact. He said he erred on the side of caution.

I'm happy with his response as I don't really want to give the head any more hassle (changing seats etc.) !! It is 39 years old !!

Cheers,

Ian.