0.028" deck height too small with H-beam rods?

[Dingleweed]

Here's the info:

CB aluminum case with +3.5mm deck
84 mm crank with Chevy journals
CB Super Race forged H-beam rods (5.5")
Clevite rod bearings
94 mm stroker pistons
CB wedge-port heads with 66 cc chambers

without any barrel shims, I measured the deck height to be 0.028" which would yield all by itself my desired compression ratio of 9.2:1

So, here's the question:
is a deck height of 0.028" enough? Does anyone know the stretch figures for forged H-beam rods?
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1962 Dune Buggy, 2332cc, W125, 44x37 wedgeports, 48 IDFs, Rancho Pro Street transaxle

[vwracerdave]

I personally do not run less then .045" deck height no matter what parts are used.
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2017 Street Comp Champion - Thunder Valley Raceway Park - Noble, OK
2010 Sportsman ET Champion - Mid-America Dragway - Arkansas City, KS
1997 Sportsman ET Champion - Thunder Valley Raceway Park - Noble ,OK

[Type 5 Joe]

I agree.... If a rod bearing goes out, you don't take out the piston, head,rod crank, ect......
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[Type 5 Joe]

Set the deck to .045 (at least).... Cut the head to the calculated CC's needed..
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[vwdragracer]

the "RODS" are not your problem. The problem will be crank flex. Even some of the high dollar forged full circle cranks will flex a bit. .045" deck minimum. Like stated set deck at .045 and adjust head cc for the desired compression ratio
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Going fast in a VW because to do so in anyything else is boring

[A.J.Sims]

sand drag 1600 with .012"
pro stock 9000rpm combos .025"
my 2387 at 13.2:1 .032"
all the motors that come out of my shop .04"
If you have a crank that will flex over .005" you need a new crank, as that one you have is rubber!
I would not run .028". its not how close of a deck that's the problem its how your checking it and with what! add .02" shim and fly cut the heads the same .02" to get the same number!
Or cut .028" off the barrel and make it 0.0" then add a .04" copper head gasket and still cut the heads.
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[camch]

are you saying run a 0 deck height and a .040 head gasket

[Dingleweed]

Thanks for the replies guys. The intentions for this motor are far from a daily driver and/or high-milage or long-term reliability motor. It's going into my weekend "toy" so it would more accurately fall into a racing motor category than a daily driver motor. I was curious what deck heights some of you racers and high horsepower engine builders have used.

[Glenn]

[Dingleweed]

[gerg]

Call over and speak to Greg - very personable and willing to help.
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Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab

[Bruce]

[miniman82]

Rods also stretch a measureable amount...
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Build thread: http://www.thesamba.com/vw/forum/viewtopic.php?t=212747

[stealth67vw]

[Dingleweed]

*Update*
I went to measure the deck height for all of the other pistons and cylinders and noticed that the cylinders weren't sitting flush with the case deck. They were binding a little between the head studs and the outsides of the cylinders. So I measured the overlap area from the outside of the cylinders (where the stud goes) to the sleeve which slips into the case. The measurements were all over the place for the cylinders... anywhere from 0.07-ish" to 0.13-ish". The clearance between the case cylinder bores and the head studs (8-mm ones) measured in the 0.11-ish" range.

Is this variation in the cylinder sleeve to head stud measurements normal for a set of cylinders?

So I used my die grinder to grind down the outsides of the cylinders in the area where the head studs are supposed to go on the case side of the cylinders. I ground them all down to be in the 0.07" to 0.08-ish" range. Now all of the cylinders slip nicely down on the heads studs and sit flush with the case.

Re-doing deck heigh measurements for all of the pistons and cylinders yielded deck heights of 0.024" to 0.025".

I think I'll be ordering a set of standard 0.020" barrel shims. This should give me a deck height of 0.044" to 0.045" and a compression ratio of 8.89:1 using the heads the way they are now (66 cc combustion chambers).

Thanks for the help guys. Oh, and this discussion of why you need deck heigh at all is very interesting (whether it is due to crank flex, rod stretch, thermal exansion of the piston, etc.)

My vote is that rod stretch accounts for the majority of deck height needed because I calculated that an 84 mm crank spinning at 8,000 rpm yields an acceleration of about 3,008 g's at the small end of the rod (assuming the piston is a simple harmonic oscillator...i.e., very long rods)
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1962 Dune Buggy, 2332cc, W125, 44x37 wedgeports, 48 IDFs, Rancho Pro Street transaxle

[Type 5 Joe]

Rod stretch isn't that much.... Grab an H-Beam rod and pull on the ends, you aint gonna stretch it that much

Imagine how many times the piston would contact the head @ 8000 RPM if you ran really tight deck height, and the rod bearing shell fails.... 133 times a second.

You had better be able to shut her down quick if you hear a problem.

Mostly crank flex, thermal expasion (piston) and carbon "use up" some of the deck clearance. I put about .045"-.050" in there, so if there ever was a problem, I might not explode my piston, rod, head, crank, case, then cam, ect, ect, .... Hopefully the piston won't contact the head a Thousand times or so before the engine gets shut down.

- Joe
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[Dingleweed]

[Type 5 Joe]

O-K imagine you're piston travelling with a force of three thousand G's or so... hitting you're head 133 times a second....
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[nsracing]

I am trying to understand how anyone can measure crank flex at all? Must be a new distortion meter somehow.

A crank will flex a lot if it has a lot of unbalance. Ultra balance work is key in building good running engines.

I like 0.040 - 0.050 myself for deck height. I mean 0.040 " is not large at all.

I am not a believer of zero deck. If you think about all the total stack of clearances from rod bushings to rod bearings and main bearings and the tolerances on the rod lenghts..end to end, I am sure it will be quite a bit of clearance.

[gerg]

My deck measured at .030" (on the thin side I know). I had some new 044 CB heads that Darren over at DRD did some mild work on for me. He told me that there was not enough material in the head to remove to get a 8.0:1 CR without major distortion to the squish area. Instead of putting a spacer under the barrel he suggested a step in the head.

So he recommended 'some' chamber work, then when cutting the head for 94mm he left a step to add to my .030" deck. The step was the same width as the 94mm cylinder wall thickness.

Overall I wound up with .030" in the cylinder, and .080 step in the head. That is a total of .110" deck - HUGE I know. Darren said large decks are not that bad and that sometimes your only option is to 'deck it' to get your CR where you want it.

I know Berg's litterature is old and fuel has changed, but he documented larger decks than that.

My engine runs fine.

Now - tear it up . . . .
_________________
Gerg

. . . I got 99 problems and my bus ain't one . . .

'65 Sunroof Beetle
'65 Vert
'60 Singlecab