6 replies to this topic

[nomininolife]

Hi Guys

As above, is it viable to turn down valves and have the seat re-cut?

I have 29.4mm exhaust valves and they need reducing by 3mm so they do not hit the block (this is to try and save pocketing for the sake of a couple of mm)

Thanks for your help

Regards

David

[MRA]

Will they still fit your head ? our valve seat inserts are 25.4mm internal diameter, your valve would have a diameter of 26.4mm so I doubt if it is going to be that easy, maybe a bespoke valve seat insert would work, or stick to a lower lift cam, as apparently this works as well

[01smartc]

Yes it can be done...

We turn down 29.4mm Valves to 26mm for our Stage 3 998cc heads.

Turn the valve down then recut the seat on the valve... you will then need to re-cut the seats in the head, if its a 998 head then you can just cut the seats a little bigger.. if its a 1275 head then you can do like above and fit some 25.4mm inserts and cut them bigger.

However i would say that fitting a 1275 head then putting smaller valves in will be a bit of false econamy as it will only flow aswell as a 998 head again.. so I hope you mean your fitting bigger valves to a 998cc head

Chris @ Smart Performance

[nomininolife]

Hi Guys,

Thanks for the replies.

Yes it is larger valves in a 12g295, 26mm will do the job just fine, it will be a lot better having the seats re-cut than having the block milled.


Thanks again guys


Regards


David

[MRA]

I assumed that this was for a 12G940 head..... because it was to avoid pocketting the block.

The issues with turning down a valve and refacing them are ......

1) concentricity
2) correct seat angle (45 degrees)

The best tooling for this is a valve head refacing and lapping machine not normally found in a conventional machine shop

If this job is not performed correctly then you may find that your valves burn out quickly

[01smartc]

I agree with above.. this is not a job for a balsa wood lathe from aldi

You need precision tools to put the seat back on the valve properly to ensure long life and performance

What inlet valve are you planning to use?

Chris

[nomininolife]

Hi Guys

I have decided after all to just get on and pocket the block, it is the easiest way to do it, when i thought about the seat and then the valve is going to be further recessed into the head thus meaning having to reduce the length of the valve stem.

So dremel meets cylinder block!!


Its going ok so far, plenty of masking and patience lol


Thanks again guys


Regards


David