Trying to wrap my head around deck height

[TouringBubble]

Ahhh ... that may be my problem! I was going on the idea that the deck height was the distance from the top of the piston to the top of the barrel, with the head not really considered (unless you consider that the barrel is mated to the head so 0 deck IS the head). So, with that though process, you could have .060 deck and 7:1 compression or a .060 deck and 10:1 compression based only on how the head is machined.

that last line was my exact thought on the matter. Thanks! Looks like I do understand it mostly.

[Chris V]

...I personally would run .035-.040" on a 94mm bore at MOST, by preference, and have run ~half that @90mm for many moons.

A 4"+ bore + forged might need .050"+ deck, depends on the alloy.
Huge bores tend to have a larger deck/bore ratio, so a tad more clearance still gives good results...

But with what stroke crank? 71mm stock rod, where this is still great journal overlap? The greatest downfall of the engine's basic design is having two rod throws between main bearings...a four cylinder engine with three and a half bearings that whizzes over 7 grand with a stroker crank in the 80-90mm range with commonly used smaller diameter Buick/Porsche rod bearings, has got such a great potential to flex.

Thinking more endurance engine building, it's also wise to leave a margin for rod bearing failure...It would be nice to have enough time to turn off the ignition before a low oil pressure secenario could mean a piston collecting the head.

[Piledriver]

RPM also plays into it, and if you have a crank like a noodle, that's an extenuating factor.

The main point was that he understand the basic concept, and that if you are going to end up at .060+ for some reason, it is probably beneficial to skip that knock inducing .060"-.100" range and go .120" if you can't make it tight.

Far more people build 1776>1914 motors vs. anything else, and the ~1mm deck target range advice usually holds.

I was running .022-.024 on a 1700 T4 (die cast aluminum block, huge mains) 66 stroke, wide T4 55mm rod journals, 127mm rods, stock redline is 5600.
Wally has run the same crank/rod combo well past 400WHP for awhile now, street driven.
About as non-noodly as it gets, admittedly.

To not whack the head if you kill a rod bearing, you'd have to run a large deck, which might be fine on a racing engine, as high RPM is the only concern, and a tight deck means little>nothing.

In my experience, the piston//ring lands take the worst of that encounter in any case.

[TouringBubble]

Well, I do plan to rev it to 6000 often. I have a forged/counterweighted crank, but am still on VW bearings. Stock case. Given that, should I be looking at more than .040" just in case? I've tried to overbuild the bottom end, but the stock case and VW size bearings would still be a limiting factor I guess.

[Piledriver]

Actually the std T1 55mm size rod journal setup results in a much stiffer crank than the smaller 2" Chevy or 50mm T4/2L journal options.

I'd run the SCAT Hbeams, but that's personal preference, as having the stock rods properly rebuilt with good bolts costs more in my experience.

[TouringBubble]

I have the CB H-beams with APR bolts. Everything in the bottom end is new, aside from the distributor drive gear, which is just a spacer in my case.

[Piledriver]

Those will work fine, and MUCH lighter than the SCAT I-beams.

[Tony Z]

I did a writeup on deckheight a while ago on our local forum, go have a look
http://www.aircooledvwsa.co.za/viewtopic.php?f=4&t=5831

[TouringBubble]

So, you measured your deck height without the barrel torqued to spec? I was under the impression that deck height had to be measured with the head (or something on top of the barrel) torqued down.

[Tony Z]

So, you measured your deck height without the barrel torqued to spec? I was under the impression that deck height had to be measured with the head (or something on top of the barrel) torqued down.

Who are you asking?

If you talking to me, then its an absolute pleasure for taking my time to attempt to help you and answer your question. But alas, dont thank me, rather make assumptions and attempt to slate me.
But no, you observe incorrectly. Just because I took photos of examples of what deckheight is without any method of holding it down, doesnt mean I didnt measure it accurately. I suppose I could have taken a photo with a plate bolted to the barrel, but then you wouldnt be able to see what I was trying to explain.

[TouringBubble]

I did make an assumption, but was in no way trying to "slate" you. I simply asked the question. I'm here stating openly that I don't know these things, and I'm asking questions about it.

I do appreciate your link and your write up, and thank you for sharing. And also thank you for answering my followup question. I'm sorry my tone didn't carry as intended.

Did you use a special setup to torque down the barrels, or did you fashion up something at home to properly torque the plate down for measurement. I can make the plate pretty easily, but I've not decided on the best way to make spacers so the bolts can hold pressure properly. I figure there is no need to reinvent the wheel if there is an accepted, simple way.

[Tony Z]

You can buy a deckheight measuring tool at almost any shop which is nothing more than a 1/2 metal plate with 4 holes drilled into it for the head studs. It comes with spacers too.
eg http://vwparts.aircooled.net/Deck-Heigh ... t-tool.htm

I used the plate (linked above) and a dial gauge

[TouringBubble]

Thanks for the info. Exactly what I needed!