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Is it possible to do calculate cylinder deck height?
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Jonasand
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PostPosted: Wed Jul 28, 2021 10:34 am    Post subject: Is it possible to do calculate cylinder deck height? Reply with quote

Is it possible to calculate cylinder deck height in a way that is "good enough" instead of measuring?

For example..

My heads where fly cut by a pro and I was told the fly cut removed about 0,2 mm

The old head gaskets were 0,75 mm (most likely as my hardware seems to be all stock and therefore the 0,75 one in the gasket set would be a direct replacement. Though I cant be 100% sure as I dont have the old gaskets anymore.)

The shim at the bottom of the cylinder was 0,2 mm

So if I remove the 0,75 headgasket and remove the old 0.2 mm shim and account for the flycut of 0,2 then perhaps I could use a bottom shim that is 0,75+0,2+0,2 = 1,15 mm

The closest I can get in the VW shop here is 1mm so that would be a deck shortening of 0,15 mm.

The guy in the VW shop told me to keep the head gasket since I'm keeping my old cylinders. He said that they probably have a groove where the pistons change directions at the top. And this groove would come further down and interfere with the pistons movement. He said I could feel it with my finger and see it if I looked inside my cylinders.

However, I don't see any groove and I cant feel one either. The cylinders have been honed also, but I don't know if that could eliminate have eliminated the groove if there ever was a faint one.

So what do you think of this? Is it good enough?
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PostPosted: Wed Jul 28, 2021 11:30 am    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

no. You have to clamp the cylinders down, measure the dish or dome, measure the head camber with a spark plug in it, then calculate it based on the bore and stroke if you know it. Each case, head etc is different. Or you can just go with what you have and hope for the best. That is what we used to do when parts were really standard new. Today the stuff is all over the place.
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PostPosted: Wed Jul 28, 2021 1:04 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Well I believe all my parts are from 1986 or older except the 1mm shim I was planning on getting. This was the year the bus got a new case.

Case, Heads, Cylinders and Pistons seem to be original German parts.
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PostPosted: Wed Jul 28, 2021 3:24 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

so you either throw your fate to the wind or you check it. You are guessing because you don't want to spend the time or money needed to check. Nothing wrong with that other than you have to be willing to accept your fate when you roll the dice. No one but God knows the what it will be just based on a guess.
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PostPosted: Wed Jul 28, 2021 7:12 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Check out page 3 of my build thread. https://www.thesamba.com/vw/forum/viewtopic.php?t=...highlight= and look at how I measured DH. I used deep sockets and washers to clamp down the pistons and cylinders to measure DH with a micrometer I got at the hardware store.

Not professional, but good enough for me and I’m pretty confident in my skills.
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PostPosted: Wed Jul 28, 2021 11:01 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

This is one good reason that I always leave the longblock with an experienced engine builder. There’s just too much to risk otherwise.
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PostPosted: Wed Jul 28, 2021 11:53 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Deck height it not hard to check. A piece of square tubing with a couple of holes drilled in it will hold the cylinder down and allow you to check the deck height with a set of feeler gauges.

If you honed your cylinders and don't have a ridge showing then you should be good to go. BTW, removing the head sealing rings and installing shims between the cylinders and block raises the cylinder slightly so the rings would be less apt to hit any ridge than if sealing rings were used, not the other way around.
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PostPosted: Thu Jul 29, 2021 8:55 am    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

I'll try this with feeler gauges, then.
My friend is coming over with the parts to build a clamp.

How do I find exact TDC without a dial indicator? Any tricks?

Do I fill fluid into the cylinder dishes and the head or is the measurement with the feeler gauges enough?
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PostPosted: Thu Jul 29, 2021 9:44 am    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Jonasand wrote:
I'll try this with feeler gauges, then.
My friend is coming over with the parts to build a clamp.

How do I find exact TDC without a dial indicator? Any tricks?

Do I fill fluid into the cylinder dishes and the head or is the measurement with the feeler gauges enough?


Same way. Build the flat stop clamp bar that spans across the open cylinder. Dead center in the bar...drill a hole and thread the hole. Put in a screw...fine thread.

Start on #1 piston.

Bring the piston up to where you see that it is close to TDC. Screw the screw down until it just touches the piston. Turn the engine opposite so the piston moves away from the screw. then reverse it slowly and carefully until it touches the screw.

Turn the screw out a very small amount and advance the piston until it touches the screw again. Repeat this until it stops touching the screw them move the screw in a very minute amount. Repeat.

Just a couple of minutes of this and you can find TDC within a few thousandths. Now inspect your fan pulley timing marks and compare to the scale or case centerline. Mark this.

Its crude but works very well.

Ray
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PostPosted: Thu Jul 29, 2021 2:50 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

You can get close by eye and touch. Just watch until you see movement, then go the other direction. Mark the flywheel in both spots at the part line with a sharpie and TDC should be 1/2 in between. Frankly a dial indicator and magnetic base is so inexpensive these days for the type work you will be doing. It will also help set the crank end play.


HF magnetic base is like $12 and dial indicator $16
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PostPosted: Fri Jul 30, 2021 4:01 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Bought a dial indicator with magnetic base today for about 45 dollars (the cheapest one) made a bar to hold the cylinders in place with bits of copper tube as spacing for the nuts like I’ve seen pictures.

Want to check cylinder deck height on #1 so need to install cylinders and pistons but having trouble with the piston pins. Using a rubber hammer but find it’s hard to get it in straight. It gets stuck. Any tips?

Also if you are there @SGKent, could you instruct me the steps involved in making this measurement with the dial indicator, if you have the time?

And where can I fasten the magnetic base since the case is aluminum?
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PostPosted: Fri Jul 30, 2021 5:31 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

you can put the magnetic base on a cylinder fin but be gentle. If the flywheel is on you can attach it to the side of the flywheel. You can unscrew the base and use a long bolt of the same thread to attach it thru a hole in the case then when you put the base back on toss the bolt and washers in the box with it because there will be times that will work better.

You measure the deck above the wrist pin on the piston top to minimize rocking. I usually let the crank rotate say .020" piston drop on either side of TDC and make a fine mark on the flywheel at the case part line each time. Measure the distance, 1/2 between is TDC. Make a mark there and you can use it as a reference when you put the timing scale on later so you can bend it so 0 is actually 0. MAKE SURE YOU ARE ON #1 cylinder when you make those marks.

for the wrist pins, use a wrench extension centered inside the pin and use a lead, brass or steel hammer on the extension. When you get it out, make sure each pin slides into the piston without binding. With light oil on it, it should slowly slide thru the piston on its own weight. If it is too tight, I use a small brake cylinder hone wrapped in 2000 grit wet and dry that has a light oil or mineral spirits on it to make a couple light passes with it. The paper is wrapped in the direction it won't bunch up. You do that just a couple times until the pin slides in and out smoothly but not too easily. With oil on it, it should only slowly fall out. That is a perfect pin fit.

when you finally assemble it, the flat side of the circlip faces out. Check each one 3 times to be sure it is fully seated in the groove.
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PostPosted: Sat Jul 31, 2021 11:20 am    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Thanks a bunch SGKent!
The sanding trick made it a lot easier to get the pins in.

We spent several hours trying to measure with the dial indicator, but we could not get it to work reliably. So we did a variant on 60vwnewengland's method above.

This is what we did, only difference is you get TDC baked into the measurement.

1. Back the cylinder down from TDC a bit
2. Push the calipers depth gauge out a bit (more then what your expected measurement will be.
3. Place the caliper as in 60vwnewengland's method
4. Push the piston up with the flywheel so the piston moves past TDC and back down again in one go.
5. Read the caliper


Link



The result we got was 0.51 - 0.52 mm (about 0.020 inches) with no shims at all just cylinders against case. Results for three tests were 0.51, 0.52, 0.52

When doing 60vwnewengland's method, we got 0.0.43, 0.53, 0.48 so a bit more variance.


What deck height should I be aiming for?

This quote by wildthings from another thread was interesting;
Quote:
You want a deck height of no more than 0.060" and no less than 0.030 unless you are being very careful in your build in which case you could go to 0.025". With uncut stepped heads, uncut block, stock cylinders and pistons, and no cylinder base gaskets you will tend to end up around .040"


For reference;
0.060" = 1.52 mm (max deck height)
0.030" = 0.76 mm (min deck height)
0.400" =1.01 mm (Everything stock deck height)

If I would add the 1 mm shims I bought the deck height would be 1.51 am I right? And that would be almost be to much if I read wildthings right.

So would adding 0.5 shims be better if aiming for a stock compression ratio? 0.51 deck height + 0.5 shim = stock deck height = about stock comp ratio?


Thanks for helping out!
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PostPosted: Sat Jul 31, 2021 1:45 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

So what do I do next after deck height?
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PostPosted: Sat Jul 31, 2021 2:26 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

the deck height is between the top of the cylinder and the top of the piston with the piston all the way up. Measure over the wrist pin area so you aren't measuring the piston rocking. With the piston at TDC put the bottom of you calipers on a flat smooth surface and zero it. Then over the wrist pin with it as level up and down as you can, measure down to the top of the piston. That is the deck. Of course the cylinder is clamped down squarely.

Next CC the heads with the spark plug in unless the shop already did it for you. CC the piston dome. Then you can use the bore and stroke with those in a compression calculator to see what your C/R is now. From that you can decide on the best shim. In a type 1 bus 8.0 is fine. In a 2L bus I'd suggest 7.3 -7.6. In a 914, 912e, or 411 etc maybe 8.0 to 8.5 depending what fuel one wants to use and how long between engine rebuilds, whether it is going to the track or not for playing around. We used to use 11.5:1 in the water cooled race car. Funny thing today is that a stock Honda that uses a computer to control timing, knock, etc., will run 11.5:1. That is how much engine design and control has improved since the 1970's.
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PostPosted: Sat Jul 31, 2021 3:41 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

What parts do I fill with water?

Are these correct (red circled area) ?

Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.

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PostPosted: Sat Jul 31, 2021 4:48 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

How far up the cylinder head do i fill with water. Is it only the ”pool” area in the middle where the valves are seated, or does the area add any volume?
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PostPosted: Sun Aug 01, 2021 5:34 am    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Ok, so I made a CC dish from from an old CD spine, after checking out this video https://www.youtube.com/watch?v=df_fwtCisMo

Put Vaseline on the edge around to seal and used ethanol mixed with a bit of blue food coloring.

I think ethanol worked better then water as the surface tension was lower. Also the color helped more then I thought.

Results;

Head volume = 53.5cc
Piston volume = 15cc
Total comp =53.5+15=68.5cc
Bore = 94
Stroke = 71
Calculated deck height for achieving 7.3 CR = 1.33
Measured Deck height without any shims: 0.52mm
Shim for achieving 1.33mm deck height= 1.33mm-0.52mm=0.81mm

Seems the CBperformance calulator rounds the cc volume upwards
If rounding down to 68cc instead;
Calculated deck height for acheiving 7.3 CR = 1.47mm
Shim for achieving 1.47 deck height= 1.47mm-0.52mm=0.95mm

If I use the 1mm shim I already bought then I would have a CR of 7.2

In Sweden we have a choice of fuel with 10% or 5% ethanol.

Should I compensate for what fuel I am going to use?


SGKent? Others? Thanks for any input, comments and correcting!
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PostPosted: Sun Aug 01, 2021 10:04 am    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

it looks like the heads have a sealing ring cast into them. If you laid the measuring tool on the chamber inside of those you need to add their depth to the deck. If you measured the cc to include them you don't add that height to the deck.

using a 7.5 to 7.6 CR will be Ok if you have good octane fuels there.
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PostPosted: Sun Aug 01, 2021 2:12 pm    Post subject: Re: Is it possible to do calculate cylinder deck height? Reply with quote

Image may have been reduced in size. Click image to view fullscreen.


I don't think I have a sealing ring. Posted above photo for clarification.
Are you referring to the lip (red line in photo) or something else.
The area where the green line crosses is totally flat.


The photo below shows where I laid the plastic disc. I smeared petroleum jelly along the outer edge under the disc to seal.

Image may have been reduced in size. Click image to view fullscreen.



SGKent wrote:
using a 7.5 to 7.6 CR will be Ok if you have good octane fuels there.


Could you please clarify your reasoning? (Just want to make sure I understand)

At first you said that a bus should be between 7.3-7.6 CR
Are you saying that 7.5 to 7.6 CR is better considering the 5 to 10 percent ethanol in fuel? If so, is this because ethanol has less energy and therefore warranting higher compression?

Is 7.3 CR the "stock" compression ratio that VW recommended?

If I use a 7.2 compression ratio what effect will this have compared to 7.5 to 7.6 CR? The reason I'm asking is that we already put everything togeather, with the 1mm shim so now I have 7.2 CR, so I'd like to know if I it is worth it to tear down again and aim for 7.5?

Thanks again for you helping me!
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