Changing piston, cylinders and cylinder heads

[rmel]

It's disappointing when you get something new and it's not perfect
But, these aren't "New" they are "New Old Stock" cast some 50 years ago.

They won't be perfect. They got moved and kicked around from one storage
loc to another. Qualitatively, they look usable to me. A figure of merit would
be the amount of material needed to seal e.g. the amount from the
inside edge of the Head Bolt hole to the outside edge of the combustion
chamber. Looks like you got at least that even at the damaged area. I've
seen worse used ones that sealed just fine. Here's what I recommend:

Get a high quality German made flat file. Place the file on the top rim of each
cylinder and just carefully run around the top surface to remove any burrs.
No removal of material other than burrs ONLY as they will mar up the soft
aluminum head surface. Next up:

Even if the heads were perfect to the eye they STILL need some hand lapping
to match fit each head to it's respective cylinder. I would also put witness
marks on each component: "One dot" mark on Cylinder #1 and Head #1, a
"Two dot mark" on Cyl #2 and Head #2 ect. INSPECT EACH cylinder CAREFULLY
At one point in time Cylinder #3 was machined slightly differently than the
other 3 cylinders -- yours may all be identical. But if one is unique around the
fins (in the up direction when installed) then that is #3. Oh, I almost forgot.
Measure the length of your cylinders, from the top surface to the bottom
flange that rests up against the engine block. There are three different lengths
yours should ALL BE IDENTICAL -- just to confirm S-Tec didn't make a mistake.
The shortest length was for higher compression. I believe spare parts are mid-length?

BEFORE you insert the pistons hand lap these mating components. I find
it easiest to lock the cylinder in a large vise, apply Valve seating compound
onto the surface then place the head in place and grind away. Use water
soluble valve lapping compound not oil based -- either works fine but oil based
is just MESSY. When done clean thoroughly with brake cleaner if you can get
it or isopropyl alcohol.

In the course of doing the lapping, a lot of that surface damage will be removed
or at least recessed below the surface -- DO NOT attempt to remove it all !! The
goal is to get a sufficient mating surface not a perfect one -- you have plenty of
meat there for a good seal, just eliminate the surface scars and planarize -- that's all.

[Hugues]

Thanks for the advice, i will still inform S-Tec, so they are aware.
I guess there is no point in bringing them to a machine shop to get the surface milled ? Enough thickness for this work to be done ?
One of the head (the one with the biggest dent actually) has a rather smooth and shinny mating surface to the cylinder. The other 3 are more rough, wondering if that rough surface is fine to seal the combustion gas properly.
Would hand lapping help for the surface finish ?

I will do hand lapping of the head to cylinder,
do i need to hand lap the cylinder to the crankcase ? or only use the Hylomar sealant you mentioned earlier ?

[rmel]

There was more than one source for casting heads. There should be a casting mark on each head.
See if they are identical. In any case, no matter how good the mating surfaces look, hand lap them.
If they are pretty good to start with then it's a quick and more of a verification. Otherwise, the one
with the scars, it will just take a bit more patience.

You could get them surfaced at a machine shop, this would be a fly-cut and that will cost you and
they may be tempted to go too deep. I'd hand lap!

You do not need to worry about the bottom of the cylinder to engine block. Just make sure the surfaces
of the block are absolutely squeaky clean. There should be a lot of sealant to scrape off with a razor blade.

I'd ask S-Tec what sealant to use. Here in the USA we can't import that sealant. I have been told that the
sealant you can source is far more viscus than what is commonly used here in the US -- Permatex Aviation #3.
I have found that the Permatex sealant is not viscus enough. There are a lot of Hylomar products. The key
is using a "Zero gap" sealant, and high viscosity. I use: Hylomar Advanced Formula High Viscosity .
Which is 4X more viscus than the standard Hylomar AF. But if S-Tec has a recommendation use that. Or ask
them about Hylomar.

IMHO the hardest part of this job is CLEANING then Sealing. There's nothing worse than doing all the work
then see Oil leaks -- been there, done that

[Hugues]

thanks for the precious advice.
This morning i was going to pick up some new windows for our bedroom and realised i was passing by the machine shop,
the guy is specialized in classic Porsche and VW, so it thought i would bring him my heads and cylinders for advice.
He was not too worried about the dents, there is enough material on each side to seal properly. He will bring the dent down just to be sure it does not protrude too much, although its aluminum and the pressure will flatten it anyway. I left him the 4 cylinders, heads and pistons for him to check valves are seated properly, surfaces are flat, rockers don't have too much play.
He clearly said that one head is not new (NOS) but reconditioned, but it appears to be in good shape, see pic below, bottom right.
I show the markings as well on each heads. Cylinders and pistons are NOS
So it'll probably cost me a couple of hundred boy for peace of mind.

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[rmel]

A shop with VW and Porche experience is ideal, your in good hands.

I'd be curious what he finds w.r.t. Valve seating. I do buy some
engine parts from S-Tec.

[Hugues]

How do we remove the front left bolt from the front carb?
I need to remove the black panel around the back of the fan?

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[rmel]

Is your goal here to just pull the carb's off or more?

The front carb can be removed W/O removing the front tin,
but requires a high quality offset wrench. Otherwise removing
the tin would make it easier. Obviously the rear carb must
have the back section of tin removed.

[Hugues]

Thanks Ron, just cleaning them for now and changing gaskets.
In about 2 weeks I'll pull the engine out to change cylinders, pistons and heads.
I just want to be sure first everything is in order before installing the new parts.

[Hugues]

Normal to have 3 gaskets between the carb and the air intake manifold ? I have only one replacement per carb.

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[rmel]

The extra thickness helps insulate the Carb's from the heat of the intake manifolds.
So you DO want thickness. One layer is not sufficient, you should attempt to duplicate
the thickness.

I can't tell from your PIX but if your intakes are not insulated, insulate them. That will
make a huge difference in preventing heat soak and a form of vapor lock. Insulation kits
are available from puch.at

BTW you do not need to pull the motor from the chassis to perform a top end job.

[Hugues]

Thanks Ron,
I will put the old ones back for now and order 4 new gaskets then, and change them when i change my cylinders.
I will pull the engine out to change cylinders, pistons and heads.
I attach a picture of my intakes, lots of gunk, but i can feel the insulation under. Can i just clean it and re-use it ?

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[rmel]

Yup, they are insulated -- good.

Hard to remove to clean, put on with an adhesive. So just air blow them clean.

[Hugues]

What's the trick to remove the idle mixture screw ?
I could get one out blowing with air,
but the other one doesn't want to come out,
i pushed it with a small copper wire, sprayed wd40 in, air pressure,...i think the gasket is holding it in.

And second picture, inside the carb, where the idle mixture screw comes out, the metal is a little broken, on both side,
should i try to remove this or better to leave it there ?

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[Hugues]

What's the trick to remove the idle mixture screw ?
I could get one out blowing with air,
but the other one doesn't want to come out,
i pushed it with a small copper wire, sprayed wd40 in, air pressure,...i think the gasket is holding it in.
...

I managed to get the second idle mixture screw out, pushing gently with a needle while turning it with a screwdriver.
Now i know why it was stuck, the o'ring is all crumbling.
I bought the carburettor gasket set,
https://www.puch.at/en/products-&-spare ... of-gasket/
i would have think these o'rings are included, but the black one on the picture below is too big, and the red one too small

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IMG_20240801_192911.jpg (283.6 KiB) Viewed 6005 times

[rmel]

There are two different Carb kits, and one difference is the Idle screw types.
You may not have the correct kit for your carb's.

That said you may find what you need in a Metric assorted O-ring kit. Nitrile
or Silicon material should work. Typically O-rings are sized by measuring the
Cross-section and Inside diameter. Measure a good old one and pick the
appropriate size from the kit.