Have you ever run a really tight deck height like .030"

[74 Thing]

Have you ever run a really tight deck height like .030" and if so did you encounter any problems?

[67rustavenger]

Nope!

You could get some "Play-Doh" from the Dollar Store and place some on top of a piston. Then install a head and valve train bits and cycle through a full revolution.
See just how close the valves are to the piston tops. Depending on the cam and lifters, You could be ok. Or find out that all hell is gonna break loose if you run that tight.
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[txoval]

I ran a .037 deck on my Okrasa engine, but that’s closer to .040

Valve clearance shouldn’t be an issue

[oprn]

My last engine came out at .037" deck, I don't normally use them but I put the paper gaskets under the cylinders to gain a wee bit more. So far so good!
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[tattooed_pariah]

So due to a series of mistakes while rebuilding my 1776 like 10 years ago.. i wound up only putting like 700 miles on it before rebuilding it again about 5 years ago.. I was living in an area where i couldn't find a machine shop that i trusted with VW heads, so I put it together the best I could..

IIRC I am currently running with a deck of about .021

I know you should never run anything less than like .026, but I did it anyway, and so far I haven't had any issues.. I am just VERY careful when adjusting timing because I know if i go too far either direction I will probably smack a valve.. :/
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[Vanapplebomb]

[tattooed_pariah]

[nsracing]

For race-only engines, I have run 0.028- 0.030" deck.

But for street engines, I stick to 0.038- 0.040" -rule.

[Brian_e]

I think a lot of it has to do with measuring skills, and how it was done.
One guys .028 might be another guys .040. Is everyone measuring at the center of the piston? Rings or no rings, feeler gauges or depth mic, torqued or not......

I have .038 on an 1835cc, and it’s great.

Brian
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[Pruneman99]

[bugguy1967]

.038" in my 96 bore Type 1.
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[jpaull]

[evanfrucht]

I'm running 0.038 too Nothing's happened yet...
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[Wreck]

You don’t need expensive tools either . I just use a piece of aluminium billet bolted diagonally across the bore and loose feeler gauges .
A little fiddly any not the best with dished pistons but it is accurate .

I’ve 0.003 deck with a 1mm copper gasket , they have been annealed and reused at least 4 times so would be well under 0.040 now . Last time I pulled a head off there was no evidence of contact . Considering a fair coating of carbon as well .

[FreeBug]

Are you guy seeing the shape of the combustion chamber printed in carbon on the piston top? Like ALL the combustion is happening in the chamber? with the edges of the piston top very clean...?

I have a very nice tool for measuring., and will run 0.97-0.96 in my latest build, so, not much lower than 38... I have street engines, tens of thousands of miles expected from the builds, My ability to measure things was pretty bad for toooo long.... and I'm chicken.

And at some point, why? The desired squish/quench needs are met.....why go looking for trouble trying to get the piston to kiss the head?

[FreeBug]

[Wreck]

[slayer61]

[Alstrup]

When we are talking super tight decks the subject becomes a little diffuse, because then we really need to know 2 things. 1. Which type of piston. And 2. Where do you measure.
Almost all cheaper pistons, even regular Mahle are a hairswidth domed. So if you measue dead in the middle of the piston you will get one reading. If you measure in the sides above the piston pin you will get another reading, which is higher. A true 0,030" measured at the cylinderwalls is at the very limit. 0,030" measured at the center of the piston you can probably get away with. True forged pistons are usually flat. So there the numbers should equall each other, +/- the inaccuracy in the rod bushings.

It is also somewhat bore related as Wreck mentioned (I thinK) The larger the bore the more deck you need in order to prevent the pistons from "tilting" into touching the heads.

In an all out dragrace engine you would find the perfect deck by trial & error. You will keep lowering it until the you can see that the pistons juuuust touches the cylinderheads in the squish areas, - or at least knocks the soot away so you have a clear shape or "drawing "of the combustion chamber on the piston top.

On a street engine you would naturally not go that tight. I have experimented a little in that direction, and I have found no real gain in anything by going lower than 1 mm (0,039") unless you go all out to race specs. You can see a slight improvement on the HC and noX, but it is minor.
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[M. Notary]

OK.. I can't. But I had to leave something.

Anything less than 0.037 will leave a mark. You can go less but everything takes a beating.

Does anyone here have an assembly manual and read it?