Deck height. What is it and how to adjust it...

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Re: Deck height. What is it and how to adjust it...

Post by 2BugMe »

Hey Tony,

Please advize if this makes sense and if i should change anything:

Stroke: 69
Bore: 88
Deck Height: 1.5 ( as per your article above)
CR: 8.5 ( want reliability and performance with W120 cam)
CC's: 47

Im trying to figuer out in which direction i must go with the head??

Thanks for the education...

:mrgreen:


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Re: Deck height. What is it and how to adjust it...

Post by Tony Z »

that all looks good.
With that cam, I would go closer to 9:1 (43cc head), but thats me.
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Re: Deck height. What is it and how to adjust it...

Post by 2BugMe »

Thanks so much Tony..

I know those piston setup is not the best.. but thats what i have to work with for now..

Please can you explain a little y you say what you say re: CR of 9:1 for that cam??? I was also thinking in that line, but was worried bout detonation if the CR was too high..

Im keen to hear what you think?? 8)

Shot :mrgreen:
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Re: Deck height. What is it and how to adjust it...

Post by Tony Z »

it is said that the more cam duration you have, the more CR you can run. Basically, you only have full compression when the throttle is fully open, so CR doesnt really cause detonation at part throttle. The higher duration cam will loose some air and fuel at low revs due to overlap, so the actualy compression wont be as high at that engine speed as a cam with less duration.
At higher rpm things get hotter, but because the time for things to happen is reduced, that will also help to avoid detonation.

Listen to when cars come up a steep hill. The ones pinging are usually driven by old ladies at low rpm cause they dont want to change down a gear.....

8.5:1 will be fine, but 9:1 should also be good. Keep with the higher octane fuel instead of cheaper lower octane.
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Re: Deck height. What is it and how to adjust it...

Post by 2BugMe »

Tony Z wrote:Listen to when cars come up a steep hill. The ones pinging are usually driven by old ladies at low rpm cause they dont want to change down a gear.....

8.5:1 will be fine, but 9:1 should also be good. Keep with the higher octane fuel instead of cheaper lower octane.
LMAO... Old ladies rock... :jerkoff:

I had such pinging with my previous airkwled years ago built by some Franse guy in PTa and the harder i rode, especially up hill under load, the more it pinged.... Retarding timing also didnt help much hey..so number 3 eventually said bye bye.. :cry:

I think i know a "little" bit more and am so glad that there is some good advice out there..

Will be keen to try the 9:1 CR.. with good LRF..

Shot TonyZ and have an awsome New Years..

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Re: Deck height. What is it and how to adjust it...

Post by Tony Z »

you too, go huge


if it pings, pull the heads off and take a few CCs out of them.
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Re: Deck height. What is it and how to adjust it...

Post by ZeroAxe »

2BugMe wrote:
I had such pinging with my previous airkwled years ago built by some Franse guy in PTa
Just for the record, that wont be me! Never lived in PTA and been a Boer all my life. Only live in France since 4 years ago, so please dont hold it against me :mrgreen:
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Re: Deck height. What is it and how to adjust it...

Post by 2BugMe »

LOL... :shock:

His name was Frans man... back in'89/'90...

U luck bast..rd... hope u choke on the LeBug advertisements over there.. :twisted:

Cant believe u exchange froggs legs and caviar for braaivleis and beer in da sun... :drunks:

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Re: Deck height. What is it and how to adjust it...

Post by ZeroAxe »

2BugMe wrote:
Cant believe u exchange froggs legs and caviar for braaivleis and beer in da sun... :drunks:

:mrgreen:
I actually only have 'Parra-boude' once.... It was the best f*kk*n Chicken I had in my life! Almost got a slap from this French chic when I said:"Jislaaik, that chicken was nice!" :lol:

Caviar, it's not all that hot.

And if only I can get proper braai brickets here, I can have a lekker braai. Ask Chris what a bitch it is to try and gooi a braai with these stupid charcoal 'strips' :evil: But all is not lost, I have a "Care package" on the way that has got a Cadac Skottel braai in it. At least there is going to be SOME Afrikaans culture here in a month or so :hangloose:

Beer is not Castle or Lion, but not that bad :drunks:


Highjack over(I think :twisted: )
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Re: Deck height. What is it and how to adjust it...

Post by Nigel A. Skeet »

Blitzkrieg wrote:Tony, what induction are you using for your 2332?EFI or big slurpy Webers?
Tony Z wrote:48 IDF webers
A few years ago at a local autojumble, I had the opportunity to purchase a pair of large-bore, down-draft Weber carburettors, for the princely sum of £25, but decided against it, on the grounds that they would be too large for my 1911 cm³ displacement, VW 17/1800 Type 4 style hybrid engine.
Tony Z wrote:In simple terms, deckheight refers to the distance that a piston is away from the end of the barrel when its sitting at top dead centre (TDC).

I then also added various bits of shim stock that I had cut to size until I ended up with a deckheight of 1.05 mm.

On a side note, the deckheight does seriously influence the quality of the combustion process. A large deckheight leads to poor mixing of the air fuel mix and a slow burn, which does tend to promote detonation and slightly higher cylinder head temps. A tighter deckheight should improve engine efficiency and cylinder head temps.

The area to aim for is a 1.5 mm deckheight or slightly less. Try not to go lower than 1.2 mm unless you have top notch equipment inside the engine as things do stretch when at speed and you dont want the piston kissing the valves or the head. I have heard of guys running down to 0.7mm deck heights, but their conrods cost more than I would like to imagine just to reduce the stretch.
If you regard a deck height of 1•5 mm or slightly less, to be the preferred clearance, why did you adopt a deck height of 1•05 mm, on your own engine?

The following two books, dedicated to rebuilding or modifying, VW air-cooled engines, include these comments about deck height clearance:


Tom Wilson, "How to Rebuild Your Volkswagen Air-Cooled Engine", HP Books, 1987, ISBN 0-89586-225-5.

Chapter 7 » Engine Assembly » Page 131 » Set Deck Height


« How Much? - Allowable deck height varies from 0•040~0•080 inch (1•0~2•0 mm). Most cylinder and piston kits are designed to give 0•060~0•070 inch (1•524~1•778 mm) on a stock case. Optimum is 0•055~0•065 inch (1•400~1•650 mm), if you feel like tinkering. »


Bill Fisher, "How To Hot Rod Volkswagen Engines", HP Books, 1970, ISBN 0-912656-03-4

Section 13 » Cylinder heads » Page 46 » Stock Head Description


« VW's ability to use higher-than-stock compression ratios is seriously limited by a large clearance (typically 0•070 inch = 1•78 mm) between the combustion chamber's flat section and the top of the piston . Reducing this "deck" clearance provides improved "squish" or "quench" as originally discovered by Ricardo in 1922. By assembing the engine so that the flat portion of the head is separated from the piston crown by only 0•040 inch to 0•050 inch (i.e. 1•016 mm to 1•270 mm) at TDC, squish is improved to increase turbulence. »

« Increased turbulence insures reasonably complete combustion of the mixture because complete combustion cannot occur at very high RPM unless the mixture is in a state of violent agitation. The cooling effect of the piston crown and the flat surface of the head combine to "quench" any "wild burning" which might start in this areaa farthest away from the plug - thereby helping to eliminate detonation. »



Another engine-building book, which mentions air-cooled VWs, in various contexts, offers the following general advice re deck-height clearance:

A. Graham Bell, "Performance Tuning in Theory & Practice - Four Strokes", Haynes Publishing Group, 1981, ISBN 0-85428-275-6.

Chapter 8 » The Bottom End » Pages 158~159


« To assist in equalising compression and combustion pressure, the crown of every piston must rise to the same point in each cylinder. This is called the deck height of the piston. In a racing engine we would want to be running minimum deck clearance to assist cylinder scavenging, and to up the compression ratio. A good solid motor with steel rods can run with a minimum of 0•040 inch (i.e. 1•016 mm) clearance between the piston crown (not the compression lump) and the squish area of the head. ..... »

« Aluminium connecting rods stretch more at high revs and aluminium has a greater coefficient of expansion than steel, so we would need at least 0•070 inch piston to head clearance. Engines that have steel rods but suffer block flex or crankshaft whip (e.g. VW), will require 0•060 inch (i.e. 1•524 mm) clearance. »



In September 2000, I met a chap by the name of John Wright-Bailey, at the Essex VW Club Show, with whom I had stopped to chat, about his 1978 VW 1600 Type 2, Zenith campervan, converted in Germany. He claimed to have been an engineer, who at one time was extensively involved in developing air-cooled, two-stroke, motorcycle racing engines. He further claimed to have rebuilt his otherwise factory-stock, 1584 cm³ AS-Series, VW Type 1 style engine, using standard-sized, stainless steel valves, a compression ratio of 8•5 : 1 and a deck height clearance of 0•030~0•032 inch (i.e. 0•762~0•813 mm), which was said to run cooler than the factory-stock engine and fuel economy of more than 27 mpg.

When I was contemplating the design parameters of my 1911 cm³ displacement, VW 17/1800 Type 4 style, modified hybrid engine (i.e. 1971 VW 411LE, WO-Series engine crankcase and associated internal components, NPR 96 mm bore cylinder barrels & flat-crown pistons and modified VW 1800 Type 2 cylinder heads), I determined that a deck height clearance of 1•20 ± 0•05 mm was readily attainable without machining either the crankcase or cylinder barrels, simply by omitting the steel cylinder-head sealing rings & paper cylinder-barrel-base gaskets. Sealing would be achieved, as per the VW Type 1 style engines, by lapping the tops of cylinder barrels into the cylinder heads, using fine grinding paste and a thin smear of non-setting sealant, between the cylinder barrels and crankcase.

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For a 1968~79 VW Type 2 engine, running on 95 RON unleaded petrol, which was becoming the norm, throughout most of the European Union, I was recommended to adopt a compression ratio of 8•0 : 1. This was achieved by increasing the combustion-chamber volume by circa 5 cm³, of the VW 1800 Type 2 cylinder heads, to 60•0 ± 0•1 cm³; unshrouding the inlet & exhaust valves, upto the inner edge of the 96 mm bore, as part of the process, for which I used rotary files on a flexible drive and cut-out cardboard patterns to check the shape. The valve heads were also reprofiled, to reduce flow resisistance, into and out of the combustion chamber.
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Re: Deck height. What is it and how to adjust it..

Post by eben »

Nigel A. Skeet wrote: When I was contemplating the design parameters of my 1911 cm³ displacement, VW 17/1800 Type 4 style, modified hybrid engine (i.e. 1971 VW 411LE, WO-Series engine crankcase and associated internal components, NPR 96 mm bore cylinder barrels & flat-crown pistons and modified VW 1800 Type 2 cylinder heads), I determined that a deck height clearance of 1•20 ± 0•05 mm was readily attainable without machining either the crankcase or cylinder barrels, simply by omitting the steel cylinder-head sealing rings & paper cylinder-barrel-base gaskets. Sealing would be achieved, as per the VW Type 1 style engines, by lapping the tops of cylinder barrels into the cylinder heads, using fine grinding paste and a thin smear of non-setting sealant, between the cylinder barrels and crankcase.
Getting rid of the top sealing ring and lapping the cylinders into the heads were recommended by VW in a later Tech Bulletin for type IV's

Also one about notching your conrods to sling oil onto the bottom of the piston.
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Re: Deck height. What is it and how to adjust it...

Post by Tony Z »

Nigel A. Skeet wrote:If you regard a deck height of 1•5 mm or slightly less, to be the preferred clearance, why did you adopt a deck height of 1•05 mm, on your own engine?
Well, as both you and I have stated, decreasing deckheight improves combustion quality and helps to reduce knocking. Since I have got some pretty decent engine parts I decided to run a tighter deck height than I would with stock conrods and an unbalanced crank.

I have also been told that I CANNOT run a 2332 without an add on oil cooler.... I have taken this as a challenge and put my cooler back into the cupboard to prove the community wrong - and if I fail, then I will accept defeat and install the cooler. This also added to my decision to run a tighter deck height.

And one more thing..... If I have any bright ideas (stupid or otherwise) which I would like to try and think might work, I wont suggest others try it first and let me know... I'll try those things on my engines and if they work, will then suggest others try it.
I have a few more ideas up my sleeves, but need time (which I dont have) to test them.
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Re: Deck height. What is it and how to adjust it...

Post by Nigel A. Skeet »

eben wrote:Getting rid of the top sealing ring and lapping the cylinders into the heads were recommended by VW in a later Tech Bulletin for type IV's

Also one about notching your conrods to sling oil onto the bottom of the piston.
Nigel A. Skeet wrote:I have previously come across second- or third-hand references, to both of these VW Technical Bulletins, but have yet to see the original bulletins, from an accredited VAG source. Ideally, I should very much like to obtain the complete set of official technical bulletins, which are relevant to the air-cooled VWs; particlularly the 1968~79 VW Type 2s & 1972~79 VW 17/18/2000 Type 2s.

One illustration I came across, showed the con-rod notching, as a 1•5 mm deep, V-shaped notch, which seems contrary to normal engineering practice re stress concentration. Unless there is a particular reason to use a V-shaped notch, associated with oil-spray efficacy, it would seem more sensible to use a semi-circular notch, to minimise stress concentration and the likelyhood of crack propagation. The so called bulletin I came across, was somewhat vague as to whether the con-rod's "big-end" bearings should also be similarly notched, or remain unmodified! Can anyone clarify the official recommendation?

Is this the bulletin re VW Type 4 con-rod notching and increased piston - cylinder-barrel clearance, to which you refer?

http://www.ratwell.com/mirror/sfraser/techbull.html
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Re: Deck height. What is it and how to adjust it...

Post by Tony Z »

thats not the same bulletin that I saw, but the info is the same.
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Re: Deck height. What is it and how to adjust it..

Post by Blitzkrieg »

How do I set the deckheight?

My 1700 Type 4 has shims under the barrels, and the original factory head gaskets.

Common advice to type 4 owners is to remove the gasket and lap the barrels into the head with valve grinding compound.

Now, do I simply do that or just reassemble everything as stock, including the head gasket?.

Or should I dispose of the head gaskets, leave the barrel shims and just reassemble and hope for the best - apparently this would increase the comp ratio slightly -BUT what about the deckheight?

Advice from experienced folk would be appreciated...
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