35 replies to this topic

[Dusky]

I d use grinding stones for your purpose, it'll be safer I think :)

[ACDodd]

If you want a margin, go for 9.5:1.

[skoughi]

I think you could be right, I always need to take the safer route!

[ACDodd]

The secret to this is to deepen the chambers. This will entail recutting valves seats etc.

Ac

[skoughi]

I don't think this will realistically be an option for me as I won't be able to get this done locally. I'm not prepared to spend money on sending the head south to get this done, more important things that need money spent on unfortunately. I'll spend time researching where I can remove material without deepening the chambers, can you help with any info regarding taking this route instead?

[ACDodd]

As I said, I deepens the chambers. How much so you need to increase the volume?

[skoughi]

Looking to increase by 2.5cc on one and 2cc for the other three.

[ACDodd]

That's about 0.030" deeper chamber and valves. Removing the beak will only get you about 1.5cc.

[skoughi]

Oh ok. I was hoping that I wouldn't even need to go as far as that. I'll need to find a lot more money from somewhere then! Getting a bit fed up with this mini lark......

[ACDodd]

No need to get fed up. This is an all to common problem. You are not the only one.

Ac

[skoughi]

Aye I know, just got a bit fed up with it last night! Got most of the rest of the engine/clutch/gearbox together today so going to concentrate on the head this next week. I also was in a local machine shop today getting some bolts and they said they would be able to sort my valve seats so at least I know I can get this done locally. Starting to think I maybe should have fitted the lower compression 21251 pistons instead then I would've been able to skim the deck and head surface to make sure they were true and clean and therefore take the c.r. up instead of the hassle I have now.

[ACDodd]

No low CR pistons are not really strong enough. The right way to do it is as you are use quality strong piston and machine the head to suit.

 

AC

[skoughi]

I see, I was wondering about the valve seats, if the unleaded ones I have in the head new will there be enough metal in them to remove the .030." that you suggest or is it a case of removing the seats then cut the .030" out of where the unleaded seat fits into?

[ACDodd]

No, usually plenty, most inserts are around .200".

Ac

[skoughi]

Okay good stuff, this may be not such an issue then if my local machine shop is able to cut the same angle on the seats then. I would imagine whatever gets removed from the seat will need to be matched in a shim on the spring side? One other issue while I have your attention my good sir, The kent 266 cam kit I bought has a set of double springs however as I'm intending to drive this thing sensibly, i.e. won't be reving the nuts off it, I feel these double springs aren't required and may end up simply putting more strain on the valve gear whilst driving at low engine revs which it'll probably do most of the time. Also since I've still to remove the valves etc from my head I'm not 100% sure the caps are suitable for double springs so if not will end up with another bill for ones that can fit these double springs. What are your thoughts on fitting these and if it's worth it for my intended driving style?