Mi16 Double Spring Head Build

[petert 550]

Here's a build of just a cylinder head, based on Kawasaki Z650/900/1000 parts and custom valves. It's still a reasonably expensive exercise however, due to the machining involved of various parts and the head itself. It's definitely not a "bolt on" exercise. When I get an inquiry to build such a head, more often than not, people are alarmed at the price. So I thought I'd outline the parts, process and typical prices involved. Then you can do it yourself! First, a summary of the parts and where to buy them.

 

36.5mm and 30.0mm long stem valves - Competition Valves Australia

VSP520 Springs - APE Race Parts

Single Groove Keepers - APE Race Parts

TVSRK1000 Titanium Retainers - APE Race Parts

33mm Shim Under Buckets - Z650's, APE Race Parts or Arrow

Spring Bases - make them yourself

Edited December 7, 2010 by petert

[petert 550]

Buckets

I'll start with the buckets as this determines the design of the valves, etc. Most Mi16 heads now have worn bucket bores, which whilst ok for street cars, are not ok for 8000+ race engines. The std. Mi16 bucket is OD32mm. A larger bucket has two advantages. It enables a clean up of the bucket bore and also more aggressive cam profiles can be used. A 33mm bucket is ideal for just a gentle cleanup without reducing structural integrity. Touring car heads I've seen had 35mm buckets but also experienced cracking across the bridge between the buckets.

 

The desired bucket clearance is very tight. The bucket should fit in the bore when both head and bucket are cold. If held in your hand for a few minutes, the bucket shouldn't fit in a cold head (at room temp). You can't have a bucket rocking around in the bore and expect to make reliable hp.

 

The machining place I use has a CNC seat cutting machine. They use the same machine for the bucket bores, thus getting repeatable accuracy with a high quality surface finish. Expect to pay $20-$25 per hole.

 

The buckets I choose are Kawasaki, as fitted originally to a Z650 many years ago. These became a popular upgrade for the drag racing Z900/1000 scene, as the shim was under, rather than on top. So they're relatively cheap ($30ish) and plentiful, but not a lot cheaper than any other after market bucket. Having no pin in the centre means a longer stem valve needs to be used. If getting new valves made it's not an issue, as you can have any length.

 

The other alternative is to use a 33mm Clio 16V bucket. They have a 14mm pin rather than 12.8mm for a Peugeot (see Arrow website). I'm unsure if there's enough clearance to get a shim in there with that extra length.

[petert 550]

Spring Bases

In this case, the spring bases do two jobs. Firstly, locate the inner and outer spring and secondly, control the spring seat pressure. I make the bases from 4140, then harden/temper. Ideally they should be case hardened to give a hard skin with a soft inner to absorb shock loads. A mock up spring base (shown) is used to measure the installed spring heights. Then adding/substracting as required, the bases are faced on a lathe to give the desired installed spring height. CNC seat cutting machines are reliable at giving repeatable seat heights, but there can still be +/- 0.5mm variation. This might vary the spring +/- 10lbs around the desired seat pressure. Using the bases to control the seat pressure means no spring shims are required, which is a bonus as the heat transfer from the spring is better, not having to pass through multiple faces.

 

The cylinder head needs to be modified to accept the spring base. Head material is removed from around the valve guide. Expect to pay $10-12 per hole for this operation.

 

It's possible to buy the spring bases. Special Tuning use to sell them for approx. $15 each. I'm not sure if they'd fit the Kawasaki springs however, and you'd still have to use shims.

 

Retainers

The APE titanium retainers are approx. $21 each, compared to $30 each from Special Tuning. Be aware that the installed height varies between an Mi16 retainer and a Kawasaki retainer, even though they're both 7mm x 7 deg. So the retainer needs to be matched to the groove position on the valve. At less than half the mass of std. retainer they're well worth the expense and effort.

[petert 550]

Valve Springs

Before making the spring bases, you need to know the installed height of the spring. The VSP520, as the name suggests, is designed to accommodate 0.520" of lift on a Z900/1000. These are 8V engines and thus have a large, single inlet valve. They run seat pressures of 120lbs and rev to 9500+. One set of springs usually does a drag race season. So handling a smaller, lighter Mi16 valve at 8000+ is a walk in the park for them. At just $11 each they're a bargain. I use a seat pressure of 80lbs. This equates to an installed height of approx. 38mm. At 0.430" lift there is 220lb. So with the desired 38mm in mind, you can measure each installed spring height.

 

This is done by trial assembly of each valve and mock up base, without springs. A tube of known length (31.85mm in my case) replaces the spring(s). The retainer and keepers are fitted to the valve. The retainer is then dropped on to the tube and the drop distance recorded. For example, if you dropped 6.00mm, the installed height for that valve would be 37.85mm. Repeat this another 15 times and you've got the data required for the spring bases. Thus a bit of labour time here.

 

Be careful when measuring new springs as they need to be cycled a few times to get a true reading.

 

Whilst the VSP500 spring also looks attractive, it doesn't have enough installed height.

[petert 550]

Valves

I get the valves from Competition Valves Australia in Melbourne. Last price was $66 per valve, regardless of diameter or length. These are premium quality, with both the inlet and exhaust made from 21/4N and tuftrided. I use 36.5mm for the inlet and 30.0 for the exhaust. The additional 0.5mm on the exhaust allows a new seat to be cut and keep the head high in the chamber. I've done quite a bit of work with John White (the owner of CVA) in developing angles of the valve, so you can reap the benefit. You can order them in any length and put groove any where you want. I've also bought them in standard length with the single groove. Then you can use the Kawasaki keeper with an Mi16 retainer. This combination works well with the Catcam single spring.

[edbar 6]

Really good read, thanks Peter! Makes me want mi rather than xu10 now!

[welshpug 1,622]

MI is an XU10

 

 

how much would this cost in total and at what kind of power/rpm levels would it be necessary?

[edbar 6]

Or an xu9! I think you get my drift though!

[petert 550]

how much would this cost in total and at what kind of power/rpm levels would it be necessary?

 

Here's typical retail pricing, including postage of parts from USA:

 

36.5mm inlet and 30.0mm exhaust valves 16 66 1056

cut seats and service head 1 400 400

port head, flow test 1 1200 1200

double valve springs 2 100 200

collets 2 20 40

titanium retainers 2 220 440

shims 16 10 160

new solid buckets 16 38 608

new inlet cam 1 425 425

new exhaust cam 1 425 425

valve spring bases for double springs 16 15 240

machine head for double spring bases 16 15 400

machine bucket bores 16 25 400

labour 12 40 480

AUS$6314

 

Provided you've got the bottom end to match, 250-280hp on 2000cc @ 8000-8500. Expensive, isn't it. You can see why builds like DrSarty's are so cost effective. It would be nice if Arrow made a 33mm bucket with a 12.8mm stem.

CF_137__Renault_Clio_16V_.pdf

Peugeot_Mi16_Solid_Lifter.pdf

Kawasaki_33mm_lifter.pdf