Gasket help and lapping

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chancee
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Gasket help and lapping

Post by chancee » Tue Feb 12, 2013 4:41 pm

Hi Guys
2056 type IV in a vw splitscreen Scat c35 cam 36 dells.
Thanks for the help some of you put forward when building my engine last year :) Having done 4k miles - last summer through Spain the Pyranees and France there was a small oil leak and a blurp/squeek when the engine turned over (sounded like air escaping under pressure but only for litterally a couple of mins whilst cold then it stopped. Therefore I thought it would be a good idea to take the engine out to have a look......

All four of the barrels were leaking very slightly where the heads mate to the barrel. (slight discolouration on the metal gaskets where they had leaked). I also had a chirp on turn over and start up, that vanished quickly when the engine warmed up – sounded like air escaping. The barrels and pistons are 96mm from a UK supplier not a branded make as far as I am aware,

Do you guys recommend the metal gasket between the case and barrells are left out (these were used)

I did not lap the barrel faces on 1200 grade wet and dry paper before they were fitted (someone has recommended I should have done this, so I am to try this and check they are flat and true).

If all proves to be ok with the barrels, I can only assume the heads might need machining back.

Any ideas guys.

Colin

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Re: Gasket help and lapping

Post by Type 4 Unleashed » Tue Feb 12, 2013 6:36 pm

What you should do on new barrels is have the tops trued at a machine shop to insure they are flat, which is trued to the bottom of the cyl's.

Then you take some fine lapping compound and lap the cyl into the head, each cyl in it's own location on the motor. That means you will not run the aluminum head gaskets, which is recommed by VW in a Tech Bullitin.

You'll need to re-calculate your compression ratio, meaning cc your head chambers and run the numbers with the deck you have and adjust it with shims as needed under your cyl's to get your C/R where you want it.
Richard

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have the money to do it right, but can always
find the money to do it twice ?”

chancee
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Re: Gasket help and lapping

Post by chancee » Wed Feb 13, 2013 2:14 am

Thanks for that so no gaskets barrel to case or barrel to head ?
Cheers
Colin

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Piledriver
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Re: Gasket help and lapping

Post by Piledriver » Wed Feb 13, 2013 2:53 am

No. Head. Gaskets.
Installing them is like installing damage.
(not my line, but it is true)

You DO need a block and heads with a flat deck, but you need that regardless.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

chancee
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Re: Gasket help and lapping

Post by chancee » Wed Feb 13, 2013 3:16 am

Piledriver hello again - thanks for responding.
Option 1 So if I go steady and lap the barrels both ends on a piece of 1200 paper (on a flat surface like glass as a base) then gently use valve compound to check for seating against the heads (checking colouration where the paste has worked for gaps). Leave out the head gasket but use the case to barrels gaskets. it might sort things?
Do you think this would be ok to do?

Option 2Alternatively I could remove the head gaskets and just bolt up, seems odd that all four were slightly blowing through.??

I am getting married in three weeks and was planning to use the van.

I am hoping thatthe above might prevent me having to use a machine shop. Which of the two would you guys recommend (if any :)). Over to you guys for your thoughts (time is running out)

Thanks again
Colin

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Piledriver
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Re: Gasket help and lapping

Post by Piledriver » Wed Feb 13, 2013 3:25 am

Toothpaste, cream not gel (gel WILL work, eventually, but not as fast as old school toothpaste) is a very fine abrasive and will show you your contact pattern very clearly w/o removing any significant metal unless you have a lot of patience.
Very easy water cleanup and leaves a minty fresh breath, or something.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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dstar5000
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Re: Gasket help and lapping

Post by dstar5000 » Wed Feb 13, 2013 4:16 am

Use a piece of glass, preferably optically correct. An old copier glas is great.

Use wet 600 paper on the glass and give the tops of the cyls two or tree twists
and turn 90 degrees, do it again and again till you have 5-6 complete turns.

NOW take a black Sharpie pen and color the tops. Do this again till there is no black
Sharpie left, about 3 complete turns.
:)

Now, just use Clover brand, fine lapping compound, waterbased for easy clean up, slathered
onto the sealing surface of the heads, works a treat and does it fast.
You will see when it is flat. IT will have a shiney ring COMPLETLY around it.

Clean up and bolt them up!
EASY PEASY!
:mrgreen:

DOn
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chancee
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Re: Gasket help and lapping

Post by chancee » Wed Feb 13, 2013 12:34 pm

Hi Don
Thanks again
Just out of curiosity what happens when you use the gasket does it cause leaks. If so that explains why all four of mine had mild leakage
Thanks again guys
Colin

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Re: Gasket help and lapping

Post by Type 4 Unleashed » Wed Feb 13, 2013 1:47 pm

Lapping the cyl's on glass will make them flat but it will not make them true, whats the point of having the cyl's flat if that flat surface is slightly angled from it's base, which sits against the case ? New cyl tops have to made true and the only way that can be done is machined.

The quality of the machining of new parts is questionable, especially from china.
The barrels and pistons are 96mm from a UK supplier not a branded make as far as I am aware,
Richard

EMW

“Have you ever noticed how some people never
have the money to do it right, but can always
find the money to do it twice ?”

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Clatter
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Re: Gasket help and lapping

Post by Clatter » Fri Feb 15, 2013 2:45 am

The big big issue that i have always found is that the case needs decked.

Doesn't matter of you finish the tops of your cylinders,
if your deck is .004-.006" taller at the center main area,
You will never get the heads to seal.

If you had all four leaking,
I'll eat my hat if your deck is flat.

Are you _sure_ you had the case decked 4K miles ago?
Last couple of rebuilds i did we decked the case, but re-used the bearings...

Sorry if it messes up your wedding plans.
Either strip it and take it in for decking,
Or slap it back together and do it right next time.

Lay a straight-edge across your cylinders to see what is up.
But beware, you will have to look very very closely to see something that is a few thou off.
And that few thou can ruin your party.
"Oh, You don't need to do all that... The valve seats are just going to fall out of it anyway!"
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Beginners' how-to Type 4 build thread ---> viewtopic.php?f=1&t=145853

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fusername
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Re: Gasket help and lapping

Post by fusername » Sat Feb 16, 2013 2:08 pm

this one time I decked my own case. 6k and no signs of leaking, but I'd never do it again. I also lappedthe hell out of my heads and got things perfect.
give a man a watch and he'll allways know what time it is. give him two and he can never be sure again.

Things are rarely just crazy enough to work, but they're frequently just crazy enough to fail hilariously.

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Gnasha
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Re: Gasket help and lapping

Post by Gnasha » Tue Dec 19, 2017 11:19 am

If you have to use shims between cylinder and block to adjust the CR will these shims seal on there own or will some sort of sealant have to be used? copper cote etc

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raygreenwood
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Re: Gasket help and lapping

Post by raygreenwood » Tue Dec 19, 2017 11:56 am

Gnasha wrote:
Tue Dec 19, 2017 11:19 am
If you have to use shims between cylinder and block to adjust the CR will these shims seal on there own or will some sort of sealant have to be used? copper cote etc

Yes....you need a sealant. It needs to be something pliable but high film strength. A good, high temp, oil resistant RTV like permatex ultra black or ultra gray.

Once your cylinders are true and lapped to the respective head positions.....put a thin, very even smear of RTV all around the cylinder base. Put the cylinders on and the head on with just light finger pressure on the nuts. You do not want to squeeze the RTV completely out.....but you want good even contact. Let it cure for most of a day.
Also....the mating surfaces must be CLEAN, CLEAN.....no traces of oil or solvent at all. I clean with carb cleaner.... then several wipes with acetone or denatured alcohol. This is important....because oils and many VOC's "can" spoil or extend the curing of the RTV. Once its cured....then fully torque the head.

The Permatex Ultra gray is the stiffest and most aggressive in grip.

Ray

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Re: Gasket help and lapping

Post by wreck » Tue Dec 19, 2017 4:54 pm

After your happy with the deck heights ,tension up the heads , leave it sit over night ,then carefully remove the heads and use a straight edge to check the cylinders are even . I got caught out recently , even though the case was decked ,all decks were within .001" of each other . I had #2 and #4 .003" shorter than #1 and #3 . (most likely the throw on the crank ) .

If they're flat all good and start assembling , if not ,shim the cylinders out . A few thou won't affect the compression that much . There's a picture on my custom shroud thread on what I'm getting at .
No matter where you go , there you are !

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Piledriver
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Re: Gasket help and lapping

Post by Piledriver » Tue Dec 19, 2017 10:38 pm

If you are lapping the jugs into the heads or block just to see if you have a true flat seal, use toothpaste.
Easy cleanup, minty fresh smell, and won't remove significant material in a hurry like even fine lapping compound will.
I suspect this was a Jakeism. It works very well and it doesn't destroy an existing good seal.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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