Sealing rings at top/bottom of cylinders

[RalphWiggam]

So now I've got my heads off and have found the cause of my low compression on #1 and #3. #1 was at 75psi hot whether or not oIL was added to cylinder. #3 was at 100psi. The other 2 were right on the money at 135psi. 1972 stock 1.7l by the way.

Turns out the "sealing rings" at the top of 1 and 3 were burned through in a small section. More so on #1. No other damage to the heads. I will have them rebuilt anyway while I have them out. There are also very thin rings at the base of the cylinders where they mate to the case. Should I remove these? The ones at the base of the cylinders measure .005" and look to be in good condition. The rings that burnt through at the top of the cylinders measure .03". Will compression be too high if I remove all of the rings? Should I leave the ones at the base alone and just seal the cylinders back up to the case with some permatex before reassembly?

[Wasted youth]

The rings at the top of the pistons where they mate to the cylinders are often referred to as 'gaskets' and there is much discussion about the 'deletion' of these on the Type 4 engine and then flycutting the cylinder heads to make up for the difference of the material thickness.

I feel compression ratio should be adjusted by adding or subtracting spacers where the cylinders meet the case... and not at the combustion chamber. This prevents any chance of compression erosion/blow through/burning like what you are experiencing.

Removing or adding any rings in either location will definitely change your compression ratio. Adding rings anywhere will lower that ratio.

What I would do, as a minimum....

Remove all case studs, re-lap cylinders to case and relap cylinders to heads. Clean thoroughly and then carefully check deck height and piston stroke. Then you will need to 'CC the heads' which means determining the area of the combustion chamber using a liquid and measuring that volume of liquid in cubic centimeters (hence the term CC). Lots of Samba discussion on this process... it's really quite important to get this right, because with these measurements are found your correct compression ratio, which goes a long way in determining engine lifespan.

[Wildthings]

VW sent out a service bulletin recommending that the head sealing rings be eliminated and you are seeing why. What you are going to want to do is mock up the engine without the head sealing rings and determine your deck height. You do not want it to exceed 0.060" and it can be as low as 0.030" and maybe just a bit lower, this requires the making of a simple jig to hold the cylinders against the block. You may well find that without the head sealing ring you will end up right in the middle of this range. You can make adjustments by installing various thicknesses of cylinder base gaskets. Assuming you are running dished pistons and your heads haven't been cut down much then your compression ratio should be fine. If you have flat top or domed pistons or if your heads have been cut excessively then shimming the cylinders out to get a deck height of .060" may be required. Going greater than .060" will be counter productive for controlling knock.

[raygreenwood]

On 1.7L heads with domed or dished pistons.....as built factory deck height measured at the edge of the piston....not on the dish or dome......factors in the head gasket (which is right at .028" thick compressed and sometimes as thin as .025") and the single .010" cylinder base gasket shim..... is typically between .075" to .079".

Removing the .028" head gasket typically brings the deck to .048"- .051".

With no other changes....this typically increases compression by about 0.2:1 or 0.25:1. The 1.7L bus with twin carbs can handle this with no problems. Removing the base gasket shim makes compression increase about 0.3:1.

A .005" to .010" flycut can take compression upwards to 0.4:1 or very slightly higher. If you need to flycut.....I would leave the base shim in. This is if the combustion chambers are still stock volume. Ray

[SGKent]

http://kentcomputer.com/77VW/techbull.pdf

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_________________
“Most people don’t know what they’re doing, and a lot of them are really good at it.” - George Carlin

[RalphWiggam]

[SGKent]

[Wasted youth]

I used a two stage valve lapping compound when I lapped the cylinders to the case and to the heads. I rotated and processed them in the same fashion you would if you were lapping valves. Sandwiched the base shim in there during the Fine stage; it's held captive by the cylinder. Cleaned everything in hot soapy water when I was done. Reinstalled all the case studs, then measured out everything to set my Compression Ratio using suggestions and experience from asiab3, sgkent, wildthings and raygreenwood, and other helpful people.

I used Permatex aircraft sealant. It's dark brown, pretty runny and you don't need nearly as much as you think. No leaks. No sealant of any kind applied to combustion chamber.

My method is not as refined as a respected machine shop, but I am satisfied with the results.

[RalphWiggam]

I don't plan on splitting the case right now. The crank play feel's just about perfect. Will confirm with gauge. I'll get some permatex aviation. Also doing the flywheel crank seal (got the gowesty one) and the oil cooler seals. The dipstick boot, Viton pushrod tube seals as well. Any other "while you're in there" items anyone knows about (without splitting the case)? Also got a new clutch disc because the old one had some oil contamination. The throw out bearing looks very clean.

[Wasted youth]

Keep in mind there is no need to split the case to lap the jugs.

Also, buying the gasket kit is a real good way to go. It's got everything but the flywheel seal.

"while you're in there"... that really depends on how deep you went. For example, if you have the heads off, then you have the exhaust system disturbed. Time to refresh that. It would be a great time to verify all the tinwork is present and not full of hole or rust.

[RalphWiggam]

[raygreenwood]

[Wasted youth]

[Wildthings]

In most instances there isn't going to be any advantage to lapping the cylinders to the case as silicone or other goop is going to be able to make a good seal here. If the jugs don't sit flat against the case, machining would be required to reface the surface, lapping would not correct this.

[RalphWiggam]

[RalphWiggam]

Here are some pics for kicks

Cam looks good. The lifters also look good.

Super dirty.

Last trip before I pulled the engine. At Stone Mountain, GA.

[RalphWiggam]

So my end play is measuring at .01". That is about double the recommended end play. Is this something that I can adjust out with shims? I will pull the flywheel off later this week and see if I can measure any axial play on the thrust bearing. I am feeling somewhat of a double click when measuring end play. That second click might be the bearing. Any other advice?

[raygreenwood]

[Busstom]

Looking at your new thread about rebuilders, it sounds like you're on the right track.

Have you figured out where all of that .010 end play is coming from? If some of that is a worn thrust surface in the case, I'm afraid you're kind of hosed...a rebuild is inevitable.

[Alan Brase]

My experience is that type 4 thrust bearings don't wallow out the case bores like in a type 1 magnesium engine. I've seen type 1 engines functioning with about .125 end play. the only limiting factor was it would affect the timing because the drive gear was hunting around so much.
Sure, change your seal if it is 20 years old or known leaking and then try to get it down to .005. But I would not lose 5 seconds sleep if it was .015, let alone ten.
Type 4 engines are super strong on the bottom. Just mind the CHT. Make sure mixture and timing do not conspire to roast the heads.
Al
_________________
Al Brase
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