Deck Height measured-now what?

Mugsy · Post by **Mugsy** » Sat Jan 03, 2004 2:39 pm

Here are my deck height specs:
#1 - 0.051 in.
#2 - 0.069
#3 - 0.055
#4 - 0.052

My engine specs:
CBPerformance Forged 69mm Cranshaft
CBPerformance stock rods
Cima/Mahle 90.5mm P&C
Total Seal 2nd ring along with other rings being stock
Aircooled.Net Level 5 heads P&P'd by DRD Racing
WebCam 163
Scat 1.25 Forged Rocker Assembly
Dual Weber 44's
1 5/8" Header with 2 1/2" Magnaflow Phat-Boy

Now then, I'm guessing I need to make all the deck heights equal...but do I want to make them equal by using copper shims(increasing the deck height to 0.069 in. on all of them), or cut down cylinders accordingly(decreasing the deck height to 0.051 on all of them)? What is "tight deck"? I'll be shooting for 8.5-9 to 1 compression ratio and I'm assuming I can run that on 87 octane, but I could be wrong.

Thanks,
Andy

mharney · Post by **mharney** » Sat Jan 03, 2004 3:09 pm

The one that is 0.069 is pretty far from the others. See if it follows the cylinder, or if you have a longer rod on one. That's fishy to me.

Eaallred · Post by **Eaallred** » Sat Jan 03, 2004 3:13 pm

Did you get those measurements with the cylinders torqued down with a deck height tool?

Mugsy · Post by **Mugsy** » Sat Jan 03, 2004 3:59 pm

"See if it follows the cylinder"? I don't get it, sorry. Yeah, thats with a deck height tool...torqued to 10 ft.lb. a la the instructions that came with it(from Lo' Cash Racing).

Thanks,
Andy

mharney · Post by **mharney** » Sat Jan 03, 2004 4:46 pm

Move that cylinder to another register and measure the deck height there.

britegreenVWSB · Post by **britegreenVWSB** » Sat Jan 03, 2004 10:16 pm

I agree with Mark. The 1/2 side is a little weird. However, the 3/4 side - you're talking 3 thousanths of an inch difference. Not worth trying to make exactly the same. That small of an amount is not going to make any difference.

TG

Mugsy · Post by **Mugsy** » Sun Jan 04, 2004 9:29 am

Well I could imagine I did something wrong too. I'll double check the #2 again today. And then if its still 0.069, then the difference could be attributed to the cylinder, the piston, or the rod. If its the cylinder, I can have it cut down 0.018". What do I do if its the piston or the rod? So, is 0.051-0.055 qualify as "tight deck", which makes for good combustion?

Thanks,
Andy

Post by **Marc** » Sun Jan 04, 2004 9:44 am

Don't forget that the cylinders have to be of even height to seal against the head, that's even more important than the deck height.
Put a long straightedge across the barrel tops, it should contact at all 4 points. If one barrel is higher than its neighbor by more than a thousandth or so it must be corrected, either by decking the case or shortening the jug.
If the piston is off by that much, it's defective. You could have the top shaved on its neighbor and then rebalance all four. It's good practice to measure all the rod lengths before you start - if this "set" is off by that much I'd get others and start over.
If you plan to leave this engine together for a long time, I wouldn't recommend any less deck with that bore size.
It's going to run on 87 at that CR but it'll be detonating any time you're into it. I wouldn't run more than 7.6 on 87 or 8.25 on 92, but what do I know?

Guest · Post by **Guest** » Sun Jan 04, 2004 10:17 am

check if the bottom of the cylinders clear the case savers... on my case this was a problem with 94mm cylinders. The cylinder didn´t sit flat on the case.

Mugsy · Post by **Mugsy** » Sun Jan 04, 2004 4:49 pm

Well Marc, you know a whole lot more than I do...I'm still flexible on the CR issure. Awhile back John told me to run between 8.5-9, and now I'm guessing he also was thinking I'd be using 93 octane, I guess I should've asked him. Well I ran into another problem, I realized I hadn't set my endplay...and that changes the deck height reading by a little over a thou as the crank moves back and forth, so I gotta take care of that first. There's an issure with that too:
http://www.shoptalkforums.com/viewtopic ... 377#416377

I suppose I'll revisit this once I'm confident my endplay is correct.

Thanks,
Andy

JC-ATL · Post by **JC-ATL** » Mon Jan 05, 2004 6:38 am

Mark's gonna pee his pants, but I, the guy who frequently disagrees with him on the compression thing, agrees that if you're only gonna run 87 octane, I wouldn't go any higher than about 8:1, 7.6 being a good conservative measure.

Post by **Marc** » Mon Jan 05, 2004 11:21 am

JC-ATL wrote:...if you're only gonna run 87 octane, I wouldn't go any higher than about 8:1, 7.6 being a good conservative measure.

With a stock engine I've found 7.4:1 to be the maximum safe for 87 octane, but this combo should be able to stand a hair more.

Andy, don't fret over the side clearance at #3 bearing, that's normal. Only #1 bearing is designed to control crankshaft endplay. I presume that your deckheight is varying because you're moving the crank beyond where it normally resides and the connecting rods are actually tilting slightly. Personally I always get the flywheel on before assembling any further, but at least take your deck measurements with the crank pushed towards the flywheel end where it will be when the engine's done.

Mugsy · Post by **Mugsy** » Mon Jan 05, 2004 2:55 pm

Thanks Marc, I've decided to just stop the deck height measuring altogether until I've got my endplay right. I'll revisit this post once I've got everything squared away.

Thanks,
Andy

Lo cash lester · Post by **Lo cash lester** » Tue Jan 06, 2004 6:44 pm

If you have readings that are way out, which it looks like you do, I would check each hole with the same rod, piston and cylinder. This will tell you if the case needs to be decked or there is a longer stroke on one or more throws. Muffler Mike shows this procedure in great detail on his web site http://216.25.126.221/mufflermike/index.html and if I can help you out with anything drop me an email.

RT · Post by RT » Wed Jan 07, 2004 11:50 am

I too found some unusual DH readings on my 1600DP pre-assemble. I was using a good AE case that had never been decked but had been align-bored .010". The crank had been turned down once but not counterweighted (I did have it balanced). When I did this rebuild, the engine had minimal hours/miles but it wasn't up to my standards and the PO had installed the 87mm pistons - yuck!. The case didn't need another align-bore and the crank only needed micro-polishing.

First I measured 1 and 2 and they were both the same - about .062" if I recall. They, to my surprise, 3 and 4 came out at .054" and .057" respectively. First thing I thought was the align-bore (done by P/O) was way off but the machine shop found it less than .001" when I later sent it in to get it decked. I also had previously measured the rods, piston pin to crown heights and all were bang on. Then I thought the Shley DH tool, which does only one cyl at a time might be the cause. So I used my thich aluminum plate and remeasured - same results. And when I put a precision straight edge across the cylinders, they were exact.

The only thing left - the crank! Whomever did the grinding, didn't get it right on. I still used the crank cause as it turned out, one of my heads measured .5cc different (both holes) than the other and after crunching the numbers, it worked out to an almost perfect volume match on all 4.

I had the case decked to give me 8.3:1 CR with no shims (!!!) and a tight DH of .042 average. I think the lowest was .038" and the highest .046" thereabouts. The snap this engine has is incredible and so far, it's running 89 octane at 30 BTDC (SVDA vacuum line disconnected).