The Official 356Talk Forum

Hate to admit my stupidity, but I'm old so I have to accept it.
I did my engine last winter and just run out of time for various reasons so
the heads was installed without machining the sealing surface. Had to install
new cylinders and lapped them with valve grinding paste to the heads.
Just slightly cleaned the surface in the heads.

At initial start the cylinder #1 leaked a little, but after couple of heat cycles,
could not hear any leak. Now when the engine is out it seem that the heads
have found their place and don't leak. Leak down "same" on all cylinders, 5-7%.

But the head nuts are not "correctly" in the heads. These are the new style nuts
with a groove and one correct washer (I believe correct as they are ground flat and
have same outside diameter as the nuts) was installed under every nut.
Torqued with a calibrated torque wrench. They are not leaking oil.

Wondering why are the nuts are angled? What did I do wrong? Look how the center
nuts overlap and short ones are not center in the hole.
Should I pull the heads and have the sealing surface machined?

(How do you folks clean the engine parts as when I look at others photos,
case and other parts look like new?)

Hello Juha,
You have your pushrod tubes in backwards. The extended ends go into the crankcase.

Apologise for the misleading photo. I have Ron's excellent pushrod tubes and
took the circlip off and pushed the tubes up so they look like being backwards.

Your heads need to be machined to the exact same depth where the cylinders seal to avoid leaks.

The surfaces where the nuts and washers clamp the head usually do not need any machining but there can be problems. You can't mix and match the early vs late length long nuts. The later type have a groove in the middle and require a washer of a very specific size. Mixing parts causes height differences where the rocker stands mount. Not good.

You also need to check each bolt hole with a magnet before fitting the head. Some washers have a tendency to jam into place in the head and you don't want to add another washer to that hole.

The washers are 2mm thick, hard, and not too large OD but suppliers have sold washers with the wrong dimensions so be careful.

Early long nuts without the middle groove do not take washers, they bare directly on the aluminum head.

All your cylinders must also be the same length from the crankcase sealing surface to the head sealing surface or you have leaks.

That left-center head bolt/nut is correct. It is probably one of the early ones with no large shoulder beneath the O-ring. The other nuts have a shoulder to keep them centered. Porsche addressed this problem later on by making a head nut WITH a shoulder, just like the other ones.
If it's not leaking oil, don't worry about it. If you have to change it and can't find a shouldered one, you can re-machine one of the other type to create a shouldered left-center nut.

For cleaning cases and heads I gather that vapor blasting is what makes them look new again. I believe it is expensive and I have not been able to find a place near where I live that does it. Glass bead blasting the heads is ok because you can't see them, but other than being very clean, the case would not look good that way, not a correct surface finish at all.

Looking at my stash of parts, I have also couple of these new style bolts.
Old style small head nut is even 18mm, new style has a 20mm shoulder.
The big head nut that go under the rockers have also 20mm shoulder but
end against washer is 19mm.
There must be a unknown to me reason why the this is 19mm
compared to the other nut 18mm. The short barrel nuts are 18mm.

Keeping the faith is challenging when I make constantly something wrong.

Juha,
Maybe you should concentrate on where you want to end up which is with same height cylinders, bearing on same depth head surfaces, about .030"-.050" crush on the O-rings, all rocker stand head bolt bearing surfaces in the same plane, and the rocker shaft at the factory location relative to the crankshaft center line.

Machining the cylinder to head mating surface isn't always necessary, it depends on the condition of the surface, and I don't think lapping is needed, but if you do machine, that will alter the rocker geometry. You can compensate with shims under the rocker stand. Front wheel link pin shims fit.

Machining the bead bolt bore bottoms will alter the o-ring crush, and the rocker height. You can compensate by machining thicker head bolt washers. (The original washers are pretty hard, but seeing as they bear on aluminum, I just machine them out of 8620.)

If you end up with too much crush on the O-rings they can split after a short while. Or you can actually bend the head floor.

If the head bolts are not in the same plane you can bend the rocker stand.

I hope this helps you.

Well explained, Harlan.

Hi Harlan,

Maybe you should concentrate on where you want to end up which is with same height cylinders, bearing on same depth head surfaces, about .030"-.050" crush on the O-rings, all rocker stand head bolt bearing surfaces in the same plane, and the rocker shaft at the factory location relative to the crankshaft center line.

I did following:
- The case was machined and the crankshaft was centred in the block.
- The cylinders have same length
- Heads was not flycut, so the even depth is a but uncertain. My height mike rod is so thick that could not measure it properly.
- Did not measure the crush on O-rings, but there is some, but not excessive crush.
- All rocker bolt surfaces shimmed to same plane and correct? height so that valve adjustment screws are in the "middle"
- Location of rocker aluminium cradle location to crankshaft was not verified, the head bolts kinda determined this.
How is this done?

Machining the cylinder to head mating surface isn't always necessary, it depends on the condition of the surface, and I don't think lapping is needed, but if you do machine, that will alter the rocker geometry. You can compensate with shims under the rocker stand. Front wheel link pin shims fit.

I'm not the first one doing this engine, had to raise the rocker cradle to get the valve adjustment screws in the middle so
rocker oiling work.

Machining the bead bolt bore bottoms will alter the o-ring crush, and the rocker height. You can compensate by machining thicker head bolt washers. (The original washers are pretty hard, but seeing as they bear on aluminum, I just machine them out of 8620.)

I probably take the heads off and have them flycut. Then either shim the rocker cradle or make shorter pushrods.

Hello Juha,

Juha Vane wrote: Location of rocker aluminium cradle location to crankshaft was not verified, the head bolts kinda determined this.
How is this done?

I usually just delta off the head. If I have to cut the sealing surface by x then I shim the rocker shaft by x. The purpose of maintaining the rocker shaft position is to maintain the rocker geometry.It sounds as if you are already aware of this as you have shimmed the rocker shaft to get the adjustment screw about right. If you are really concerned, then you can put an indicator on the valve retainer and measure the valve lift vs crank angle and check the rocker geometry. Of course, adjusting the pushrod length is an alternative to shimming the rocker stand.

Since the leak down is very good it is not clear that machining the sealing surface will improve anything.

If you do machine, you must maintain the depth of the sealing surface shallower than the space between the top of the cylinder and the first fin. If you have to cut the sealing surface too much only then do you have to machine the bottom of the head to get the clearance back.

What is this "vapor blasting"?
Me thinks it is abrasive particles suspended in liquid.

I have heard of the mysterious "vapor honing".
Also likely abrasive suspended in liquid.

So we don't sand blast engine parts. We vapor blast them.
Tell me I am wrong. And tell me how vapors abrade a surface.
I am skeptical.
No abrasives left behind when done?

I don't know much about it and I haven't found anybody near me to do it but vapor blasting produces a like new surface and is not as risky as bead blasting. I never bead blast an engine case.

read this
https://www.vaporblastingequipment.com/ ... ng-process

http://www.arnoldsdesign.com/Gallery.html

If you scroll down there are some before and after photos that are pretty impressive.