33 replies to this topic

[kyle9832]

First I would be assembling it and make some measurements to check that you do actually have a real and not perceived issue.

then there is the other option of sell head and get another more suitable.

you are correct, I could be worrying over nothing but I was just checking my options if I do find it does hit the bock

[kyle9832]

By far the cheapest/easiest would be to recess the valve into the head. But you can only do this a limited amount, so it will depend how much clearance you require.

Phil.

the valves are already to tall for my roller rockers and I have had to use shims so I think if it does hit I will have to get the block pocketed... cheers for the help

[blacktulip]

What size pistons have you got?

+60 nural flat top pistons

Really? With 23.5cc your cr is gonna be really high. I'm building a similar spec but I have been told to aim for 26cc with the pistons flush to the deck. That should reach around 9.5:1 cr.

[Turbo Phil]

They will be 1275 valves, that's why they're longer. I've just reread your original post and realised you're just pushing them down by hand. You need to do a dry build and see if they still hit with the cam/rocker combination you're using. It might be fine.

Phil.

[kyle9832]

 

 

What size pistons have you got?

+60 nural flat top pistons

Really? With 23.5cc your cr is gonna be really high. I'm building a similar spec but I have been told to aim for 26cc with the pistons flush to the deck. That should reach around 9.5:1 cr.

 

the c.r will be 10.5.1 which is ok as I will be using super unleaded so should be fine!

[kyle9832]

They will be 1275 valves, that's why they're longer. I've just reread your original post and realised you're just pushing them down by hand. You need to do a dry build and see if they still hit with the cam/rocker combination you're using. It might be fine.

Phil.

yes I hope so, I was just seeing what options I had if it does hit the block, I will update when I do the dry build

[blacktulip]

 

 

What size pistons have you got?

+60 nural flat top pistons

Really? With 23.5cc your cr is gonna be really high. I'm building a similar spec but I have been told to aim for 26cc with the pistons flush to the deck. That should reach around 9.5:1 cr.
 

the c.r will be 10.5.1 which is ok as I will be using super unleaded so should be fine!

Should be a little pocket rocket when finished :)

[kyle9832]

 

 

 

 

What size pistons have you got?

+60 nural flat top pistons

Really? With 23.5cc your cr is gonna be really high. I'm building a similar spec but I have been told to aim for 26cc with the pistons flush to the deck. That should reach around 9.5:1 cr.
 

the c.r will be 10.5.1 which is ok as I will be using super unleaded so should be fine!

Should be a little pocket rocket when finished :)

 

oh I hope so! haha:)

[kyle9832]

I did a bit of a dry assembly with just the cam and a pushrod and found out of all 8 valves, only the far left exhaust valve touches the block, the rest clear it fine, and it touches it by a hairline, and i mean very small ammount! What are my options here? Machine the radius a tiny bit off the valve on a lathe? Pocket the block on one bore? Any ideas?

Edited by kyle9832, 13 June 2015 - 09:38 PM.

[blacktulip]

Did you fit the head gasket?

[kyle9832]

no but it hits the block no where near its full lift so I don't think that will cure it, and I would rather it didn't touch the block like the rest of the valves, it is only about 20 thou (0.5mm) to big and just clips the very edge of the valve...

[blacktulip]

Something seems very wrong with this. The valves don't usually go into the bores much. If you pocket the block you will upset the cr on that cylinder. It may be worth looking into having the valves recessed. Or speak with vmax about what's going on.

[kyle9832]

Something seems very wrong with this. The valves don't usually go into the bores much. If you pocket the block you will upset the cr on that cylinder. It may be worth looking into having the valves recessed. Or speak with vmax about what's going on.

all the bores have been bored out to +60 aswell so if they hadn't it probably would be touching the exhaust valve on all of them!, but as I say its a hairline touching the valve! such a small amount, im thinking like moke spider says the manufacturing tolerances were rubbish when the heads were produced so that valve is half mm further to the side than the rest, causing it to touch the bore, it has larger valves and is skimmed ALOT so is very close to the top of the block and has big valves! just seems strange its only on one!

[blacktulip]

I would still sit it on the head gasket and see what its like. Also might be worth seeing if there is any movement between the studs and if they are straight.

[timmy850]

I have a 12G295 with 32 and 29mm valves like yours. It's also been skimmed a bit as well. On a +040 998 block the exhaust valves just hit the top of the block. I was planning on using it with +080 flat top pistons which should solve the problem..

When I install the collets with no springs the valves stick down this far, which would be absolute furthest it could go. I'm not sure if the springs would bind first?