Max/Min Deckheigth 1.5mm

[Eddie DVK]

Ok,
If had this question for a long time now.
I always see something about a 1.5mm deckheight rule.. only the thing is should you not go less / or greater ? than 1.5 mm on the deckheight.
What is meant by this. I hope it makes sense what I wrote down. 
I really like to know.

Regards Edgar

[Erlend / bug66]

More is useless because you will ignite the air/fuel mix in the cylinder, not in the combustion chamber.

Less is ok in my books. 1,2mm will handle 9200rpm

I will not test any less 

[kb]

I'm running 0.85mm in my 2332cc. 8'000+ rpms. Haven't had any issues yet. Will know more when I remove the heads in the winter though.  

I've always been recommended approx. 1.2mm. Alot more, and you will have a lot less efficient engine, and some say hotter running aswell. Go too tight, and you risk contact as parts stretch and expand. That's more of a problem with cheap parts though.

[spanners]

I run 1mm om my race Wassers, it's on the limit believe me!  The Bore size is a big factor, small bore can run tighter deck,   how can you test you are at the limit?
A little trick I use is to mark my pistons information in strategic places with an auto centre punch, this raises a 'crater rim' round the marks , the raised area becomes polished and is mirrored on the head, so I KNOW I'm about 002"/003" from contact, my pistons are 98mm, The trouble is, if oil pressure drops, or a b/end shell fails, it will hit the top, also the Wassers do not expand like air cooled cousins, another fact to bear in mind, I'm down to 080" piston to valve clearance, another factor, so personly for my air cooled builds, i go .125" piston/ valve on the air cooled exhaust valves were there is a big expansion factor in the valve and piston height, versus the overall engine expansion, hot valve clearance is a good expansion guide, I only open up from zero lash to 003" hot on the Wassers.
Air cooled Deck I go 1.5 mm 90.5 to 92/94 bore, only 88mm or smaller bore gets down to 1mm,  I've run 50mm bore at 025"/.027"  deck for instance.

[Eddie DVK]

I run 1mm om my race Wassers, it's on the limit believe me!   The Bore size is a big factor, small bore can run tighter deck,   how can you test you are at the limit?
A little trick I use is to mark my pistons information in strategic places with an auto centre punch, this raises a 'crater rim' round the marks , the raised area becomes polished and is mirrored on the head, so I KNOW I'm about 002"/003" from contact, my pistons are 98mm, The trouble is, if oil pressure drops, or a b/end shell fails, it will hit the top, also the Wassers do not expand like air cooled cousins, another fact to bear in mind, I'm down to 080" piston to valve clearance, another factor, so personly for my air cooled builds, i go .125" piston/ valve on the air cooled exhaust valves were there is a big expansion factor in the valve and piston height, versus the overall engine expansion, hot valve clearance is a good expansion guide, I only open up from zero lash to 003" hot on the Wassers.
Air cooled Deck I go 1.5 mm 90.5 to 92/94 bore, only 88mm or smaller bore gets down to 1mm,  I've run 50mm bore at 025"/.027"  deck for instance.

Ok I think I am getting it..
spanners I know on engines the exhaust valve should be set at about 2.0mm clearance (0.080) but how do you meassure this on an aircooled engine, cranck and cam are rotating together... any trick? or do you guys use the child clay?

[spanners]

Valve to piston clearance is best checked and set at the build stage, much harder to do later after any  engine upgrades, new heads or such, it's very easy to bend a valve  even just checking. I start with light springs and no pushrods after finding the overlap phase on the.cylinder concerned, then hand operate the valves to see the clearance I have, if any, it's normally plenty on stock rod length builds, it gets more dangerous with long rods or special piston and liner builds, some odd builds may use a negative deck and need lots of valve pocket work, but starting with a visual deck clearance Check before the heads go on is safest, setting from zero deck by shimming the heads is were the problems need looking for with great care..

[kb]

Ok I think I am getting it..
spanners I know on engines the exhaust valve should be set at about 2.0mm clearance (0.080) but how do you meassure this on an aircooled engine, cranck and cam are rotating together... any trick? or do you guys use the child clay?

I put clay on the piston, and installed the head and pushrods on that cylinder. Then I turned the engine by hand. Then machined down a bit, trial-fitted it, and machined a bit more until I had the clearance I wanted. Maybe not the best solution out there, but it's easy, and it works.

[jaqo]

My friend tested it (not intentionally:D The case was badly machined and he didn't check or something)
2276, mahle B pistons, rpm up to 7000
Cylinder with 0.85 deck - no problems
Cylinder with 0.80 deck - almost no carbon deposits on the head or on the piston but not touching
Cylinder with 0.75 deck - slight contact.

[DWL_Puavo]

1,2mm deck height in my endurance engine (2274cc, wiseco pistons), no problems flat out up to 6500rpm few hours on track. After teardown, no contact anywhere, minor soot deposit layer on piston. Layer was almost transparent in squish areas. We currently shim all of our built engines to 1.0 - 1.2mm if possible in the wanted static compression range.

[kb]

Disassembled my engine today.
Here's the result from 0.85mm deck height, 2332cc, 13:1 compression, E85 and 8'000+ rpm. No visible contact, and relatively clean pistons/heads. The desposits you see on the image below was easily wiped off the pistons with just a cloth.

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