valves

[street]

As part of my engine rebuild I am getting a new set of valves as the stems are at limit to be cut down any more. I am getting frustrated on 3rd parties lack of urgency in sourcing a new set (from USA) apparently the exhausts need to be .5mm oversized?
I have a standard head, is this anyone has come across before, recommend options etc. I have been waiting three months now so all options will be considered.............

[rgh0]

I have never had any issues sourcing valves either standard or large size long stem competition versions. But you are after special standard length but 0.5mm oversize head valves which are not a standard item so a wait may be expected in these Covid times especially.

It sounds like your valve seats have been cut / ground to many times and your valves have recessed and the valve stems ground to get adequate clearance. Is it being recommended that you fit oversize valves and recut the seats to suit ?

Normal practice would be to fit new valve seats but I guess it is probably possible to fit oversize valves with re-cutting of the existing seats depending on the rest of the head details.

cheers
Rohan

[street]

Rohan,

"it sounds like your valve seats have been cut / ground to many times and your valves have recessed and the valve stems ground to get adequate clearance. Is it being recommended that you fit oversize valves and recut the seats to suit ?"

From what I understand yes, the engineer has told me the meat left on stem for collets would be minimal.

The 3rd party in between is the one sourcing parts from JAE? in USA. Apparently another update tomorrow.

In your opinion, new valve seats, better overall option, i see they are reasonably priced at Burton Power.

[2cams70]

If it were me I'd be immediately getting my engine out of that workshop as far and as fast as possible. The suggestion to increase the exhaust valve head diameter by 0.5mm to compensate for valve seat recession is extremely poor advice. There's good reasons why you can't get off the shelf valves to this specification. These valves are for a pedigreed Lotus Twin Cam engine and not for some pre-war kerosene powered Lister stationary engine. You have been warned - they could cause you a lot of extreme heartache and expense further down the track!!

[rgh0]

Rohan,

"it sounds like your valve seats have been cut / ground to many times and your valves have recessed and the valve stems ground to get adequate clearance. Is it being recommended that you fit oversize valves and recut the seats to suit ?"

From what I understand yes, the engineer has told me the meat left on stem for collets would be minimal.

The 3rd party in between is the one sourcing parts from JAE? in USA. Apparently another update tomorrow.

In your opinion, new valve seats, better overall option, i see they are reasonably priced at Burton Power.

Yes you don't really want to go much under 0.1 inch / 2.5 mm of groove top to valve stem top otherwise you can affect the collet stability so you do need to do something!

What shim thickness are you down to as you can potentially go thinner than many think? You can also fit thinner followers to enable thicker shims.... lots of relatively cheap options

Its not a normal solution to recut the seats for a slightly larger valve heads to restore the valve seat height. No reason it could not work.... just unusual for a Lotus twin cam.

Seats are cheap.... but the fitting of new ones expensive and you need to make sure the shop doing it does not overheat the head and gets the right interference fit so they are properly secured. Every time you heat a twin cam heat you shorten its life so its not something you do if you don't have to.

I know NZ is the heart of engine innovation but I would personally want to see the details of what's being proposed ( and know the providence of the shop being used) before I could endorse it over a conventional route of replace the seats and use standard valves solution.

If your not planning on ever selling the car then building a non standard engine is a risk you can take, and something I do often in the name of performance! Hopefully any future owner can figure out what you have done if they ever have to pull it apart


cheers
Rohan

[2cams70]

Normal practice would be to fit new valve seats but I guess it is probably possible to fit oversize valves with re-cutting of the existing seats depending on the rest of the head details.

Agree but typically with a cheap machinist the larger valves will be dropped in without the requisite opening out of the throat area and blending in of the valve seat area to match the larger diameter valves (been there done that). It takes considerable time and effort to do this properly. If not done properly your flow will be worse than with standard size valves. In any case the standard exhaust valves are already large enough in a Twin cam unless you need something for racing. Bigger is not necessarily better.

Your machinist probably doesn't have the skills necessary to do the job properly to replace the seats which is why this is being suggested. New seats will be better able to cope with the effects of unleaded fuel too which will help avoid recession in future. If you are going to replace the exhaust seats you may as well do the inlets too as well as fit the larger Sprint spec. inlet valves.

As a matter of interest what other work is he proposing to do the head? Usually cutting the seats is only just the start of it!

[Craven]

New seats are the correct way to go, BUT you could use new thinner pad cam followers/buckets if you are just looking for extra 0.050” clearance. May be an easier option.
https://qedmotorsport.co.uk/product/cam ... -thin-pad/

[street]

Paramount engineering, north shore, NZ - they come very highly recommended are extremely busy and being NZ still have lots of old engines coming in for work.

I do not have an issue with these guys, feel free to take look.

In discussion with them this morning, the inlets have been cut down to much and seats need refacing, exhausts are fine but i need new valves as stems are worn.

The ranges for new valves to avoid new seats are follows;

Inlet – Minimum 1.565” – maximum 1.580 diameter. Shaft Length – 98.5mm max, can go shorter. Shaft 5/16th

Exhaust – Minimum 1.325” – maximum 1.340 diameter. Shaft Length – 97.5mm max – 97mm minimum. Shaft 5/16th

I have gone to SJS and Burton power, any other suggestions

[promotor]

Paramount engineering, north shore, NZ - they come very highly recommended are extremely busy and being NZ still have lots of old engines coming in for work.

I do not have an issue with these guys, feel free to take look.

In discussion with them this morning, the inlets have been cut down to much and seats need refacing, exhausts are fine but i need new valves as stems are worn.

The ranges for new valves to avoid new seats are follows;

Inlet – Minimum 1.565” – maximum 1.580 diameter. Shaft Length – 98.5mm max, can go shorter. Shaft 5/16th

Exhaust – Minimum 1.325” – maximum 1.340 diameter. Shaft Length – 97.5mm max – 97mm minimum. Shaft 5/16th

I have gone to SJS and Burton power, any other suggestions

G&S Valves (ie REC Valves) make Lotus Twincam valves (amongst plenty of others) and are as good a quality as you will need (and can make custom valves too):

http://www.gsvalves.co.uk/

http://www.gsvalves.co.uk/assets/race-e ... alogue.pdf

[rgh0]

Standard big valves for inlet and standard exhaust valve sizes are at the bottom end of your head diameter range. You can probably get more flexibility in acceptable length by using thinner followers so standard valves may still be a possibility. There are lots of custom valve makers around and I would have thought there would be someone in NZ that could make you valves more in the middle of your target range if standard valves cannot be made to work

cheers
Rohan

[alan.barker]

In Auckland maybe Jim Gamsby who works on TVR and LOTUS could suggest something.
Alan