8000 rpm/300 bhp 3.2 rebuild

[911hillclimber]

Thank you Tim; I'll be making one as the alum bar is awaited off ebay, Tuesday delivery.
I know how it works, just needs some careful lathe work. however...
If I fail I will remember your offer about Xmas time when I hope the JE pistons will arrive (maybe)

I shall practice on my old 3.2 pistons to test my efforts.

[Magnum]

Hi Graham

It seems Design911 aren't brilliant with customer feedback and dealing with issues such as your "missing/out of stock" main bearings and chains. I've certainly had frustrating experiences.

Given the time-critical nature of your build you might want to touch base with "Type911" on Impact Bumpers (where you're also posting) - he seems to deliver a more personal experience, coupled with great knowledge.

Just a suggestion....


BTW - after your recent comments about a brilliant feeling 915 gearbox, did you get any insights as to why it was performing/feeling so great. I've still got that occasionally baulky shift up/down into 2nd gear that we share....

[911hillclimber]

Thank you.
I've used Type911 many times over the many years and they are indeed good at Customer Service.
Des911 have much the same stock but Des911 offer the discount that can add up, I had 7% this time round.

I like 'one-stop-shopping' for simplicity.

I will chase Des911 for an update again to see what is happening. If I am still without the bearing shells and chains at the end of Nov I will change tac, cancel and find parts possibly at type911.
Chatting to many at the DDK swap meet yesterday it seems there is indeed a supply of parts issue.

As to the shift.
The box is a untouched 915 on it's original clutch and 70K miles old. The coupling bushes were changed recently for slop to round hole bushes (as my car is) and adjusted. This was by a garage who had not done it before. The change is fabulous.

I managed to buy the only 915 stock gearshift tower there yesterday, and will fit this in the spring as the 911 is in storage right now.

I can't help feeling it is all down to original parts.
That SC felt like it would have left the factory that way.
It is a remarkable car (and for sale!)

[911hillclimber]

Greatworth Classics will be installing the WEVO Gateshift for me at the end of Nov, back to me for Xmas.

I've been cleaning and degreasing etc the main cases and various bits, and taking the heads to the HeadShop tomorrow for twin plug machining.
They will be back for end Nov latest, and if I can get some titanium valve spring top hats I can at least build the heads up read for the Big Assembly.

Found I had ordered some wrong parts through Des911, but they have sorted that, so have a small(!) list of things to order, again so if the pistons/rods turn up in Xmas ish time I'm ready.

I really want/need to have the engine built by end Jan/mid Feb (2022).

I think I will be forced to sell the lovely Honda CB 175 and my Peugeot BIMA to help things along and keep the peace a bit, but that will be late spring time.

So financed, I can go Clewett twin spark module.

[911hillclimber]

Getting bored now while I wait for parts which are about 2 months off yet from the USA.

Made a knock-off of the Stromski Racing wrist pin clip insertion device.
Anyone who has inserted these know they ca be a very free spirit when they escape, and hard to find after landing.
Made it, tried it, and it sure works well!

Cost: £0.50

[MikeB]

Well done, Graham, certainly a handy tool, when I changed to the Wossner slipper style pistons, the Stromski tool was the only way of fitting those springy little blighters Mind you I stilll make sure I have all the openings into the crank case blocked off, just in case

[911hillclimber]

Yes, you hear a very satisfying 'click' as the clip snaps into place. Nice to make on my 1937 lathe, a beautiful tool to have in the garage.

[MBEngineering]

"Getting bored now while I wait for parts "

you could have been looking inside your gearbox to see what condition it is in, but

[911hillclimber]

You won't catch me in a Porsche box.

I think the box has done about 500 gearchanges since you did it Mike.
There were some slivers on the mag plug when I drained the oil, prob the reverse gear that could crunch at times, but ut functions well, just the lousy gear linkage...

[911hillclimber]

Anyone with real experience of racing valve springs?
The Kent items (usual twin springs) are such that the inner spring is a light interference fit to the inside of the outer spring. Stock springs have a large clearance by comparison.
Coil springs increase their diameter when compressed, so the outer spring will expand more than the inner so there may be a clearance when installed and working.

Is this reasonable thinking/assumption?

[RobFrost]

No real experience, but gifted at physics etc. To my mind I see no reason why the diameter of the outside of the inner spring will expand differently to the diameter of the inside of the outer spring. Moreover, it sounds like you're imagining they would rub. But since they're compressed in unison there will be no significant "rubbing" movement relative to each other in service, to cause wear. Light interference is probably the best situation because it will prevent distortion radial to the valve's axis which could bring them into contact at isolated points, yielding much greater localised pressure (due to a. carrying radial momentum followed by impact and b. contact occurring over a smaller surface area) and thereby causing localised wear on the springs.

[911hillclimber]

Thank you Rob, good to read.
On another (hillclimb ) thread, I had this from a Professor in engineering recently who I've known for many years, your views are the same which is assuring. The Sping set cost over £400 so need to be right.

Titanium tops

Hi Graham, my two pennyworth:

I had a similar question with my 2l dohc C20Xe. It seems to me that the resonant frequency of the valve spring stack needs to be well below the forcing frequency of the engine, remembering camshafts rotate at 1/2 crank speed. So at 8200 rpm max the cam goes at 4100 rpm = 68.3 Hz.

Mass of inlet valve stack = 34mm valve (55.5gm), 1/3 of spring mass (13gm), steel valve cap (15.5gm), collet pair (2.3gm), cam follower (38.3gm) and shim (2.3gm). Total = 126.9gm. NB: Use 1/3 spring mass for dyn calcs.

Mass of exh. stack with 29mm valve (47.4gm) otherwise same = 118.8gm.

I fitted the inlet valves with Ti valve caps (9.4gm) which reduced the stack mass to 120.8 gm, i.e very close to exhaust valve stack mass.

The resonant frequency (Fres) of the inlet stack = 1/2Pi (sq. root K/M) where K is the spring stiffness of 47N/mm for my QED double valve springs.

Doing the sum this give Fres = 99.2 Hz i.e. well below the forcing frequency.

So, because the inlet valve is always heavier than the exhaust valve (typically 1.15 x the head diameter), Ti valve caps on the inlet valves brings the 2 stacks close in mass, which seems pretty ideal to me and only half the cost!

Racing Springs:

Hi again Graham. I think that is standard practice for there to be a light interference between inner and outer springs – it provides some friction (Coulomb) damping which will be useful vis a vis the harmonic oscillations we saw in DD’s YT link. Mine are exactly as you described in their fit.
Incidentally Dennis mentioned spring rotation: well because of the deliberate offset of cam lobes relative to followers, so they will rotate, there is always same torque applied to the valve assembly and with Rob’s inertial effects it may not be so surprising that the whole assembly might slowly rotate at high rpm.

[911hillclimber]

Really twiddling my thumbs now...

The racing springs are correct with slight interference fit according to Kent Cams. Stops the springs from vibrating.
Have to use the titanium caps with the springs, stock steel ones will not fit, 12 caps here thanks to a ddk'r.
Installation length of the racing springs is 36mm. Not sure what tolerance is on that. (+/- 0.1mm?)
Stock installation length for both valves is 34.2/34.5mm

Not convinced the shims in the heads removed will give me 36mm so fingers crossed. Approx. 1.6mm to come out.

Heads should be back in 2 weeks time from m/c to twin plug, so can be built up while the long wait for pistons/rods continues.(update requested)

Might have to do the garden instead....

[PeterK]

Really twiddling my thumbs now...

Might have to do the garden instead....

You're welcome to come and do my garden !

[911hillclimber]

No chance.
I (used o) have a phrase:
'If I can't weld it, I'm not particularly interested'

Still stnds, but if I'm bored then I will set my mind to it.
Raining tomorrow, so got out of the sweeping up of the carpet of leaves dropping, so will make a Valve Spring height device.

Looks simple enough if I have the materials and can find a light compression spring.

Each spring set needs to be 36mm +/- 0.1mm

Can buy the Porsche tool, but £100!!

https://th.bing.com/th/id/R.2d3aeff2f6c ... ImgRaw&r=0