8 replies to this topic

[Zik]

Hi all, I'm working on a 12G940 head at the minute, learning to port and polish etc and while I'm working on it the valves are looking a little tired and I think they could do with replacing along with the springs and guides.

The valves are standard big valve dimensions - 91mm by 29 and 36mm, with a single grove collet. I'm also planning to fit 200lb double valve springs and new iron guides.

 

Does anyone have any recommendations for valves? I can't really justify the expense on rimflos, but minispares have valves at 10 pound a pop - does anyone have experience with these?

 

Valve guide wise, I've seen plenty of arguments between iron and bronze but I think on the spec of engine I'm building I would rather have the reliability of iron - is this a bad idea?

 

Are double valve springs worth it? Is 200lb a good weight for an SW5-07 cam with 1.3 rockers? Do I need the lower guide for the inner springs to sit on? What top caps and collets do I use?

 

Finally, does anyone know where I can get a punch or drift for knocking guides out of the head? All the ones on ebay have too great an inner diameter to fit in mini guides.

 

Is the sky blue? Sorry too many questions :)

 

Cheers

 

Zik

 

Edit: And to save me making another thread, has anyone thought of blanking the heater take off and using a sandwich plate to feed the heater and act as a bypass to avoid drilling umpteen holes in the thermostat?

Edited by Zik, 12 September 2013 - 05:40 PM.

[racingbob]

valve spring to suit revs your going to use, you probably don't need 200 lb

[Zik]

In all likelihood the engine will never see more than 5k rpm - what weight would you recommend? 

[minimadles]

iron guides are fine on chrome plated valve stems eg. standard valves if you up grade to stainless valves you would have to fit  bronze guides. after fitting new guides the valve seats will need re-cutting and the guides will probably need reaming back to size to restore stem to valve clearance .the vizard yellow bible is where you need to look for head tuning and valve shapes

[Zik]

iron guides are fine on chrome plated valve stems eg. standard valves if you up grade to stainless valves you would have to fit  bronze guides. after fitting new guides the valve seats will need re-cutting and the guides will probably need reaming back to size to restore stem to valve clearance .the vizard yellow bible is where you need to look for head tuning and valve shapes

 

Thanks, yep have a copy of the big yellow bible in front of me! It doesn't, as far as I can tell, reference spring weights though (unless Im being blind!). I think the ream is 9/32" and some seat work was on the cards anyway as I'm considering an unleaded exhaust conversion.

[minimadles]

yes ream is 9/32 page 293 and 294 for some info on springs

[Zik]

yes ream is 9/32 page 293 and 294 for some info on springs

 

Thanks, think I have a different addition as springs are on 318 in mine but I was looking in totally the wrong section! Cams not heads 

[Zik]

Another question valves like http://www.minispare...px|Back to shop

those, have a thinner stem section close to the valve face. Obviously that's better for flow but does that impact valve life or durability?

[Turbo Phil]

The race valves with waisted stems are a high grade stainless & one piece, so are stronger than the road spec two piece valves. {where the heads can come off if used at high rpm for prolonged periods} 
If you're going to keep the revs under 6,000rpm the road spec valves & iron guides will be fine. If you have access to a lathe the road spec valves can be modified as per the Vizard book & will flow as well as the race valves at the lifts you'll see.
As you already have single collet caps & collets buy the single collet valves to suit.

Phil.