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-   -   Deck height - take my chance ? (http://forums.pelicanparts.com/911-engine-rebuilding-forum/276154-deck-height-take-my-chance.html)

hobieboy 04-08-2006 09:08 PM

Deck height - take my chance ?
 
Decision decisions...

My deck height measured to be ~0.7mm. That is a bit less than the "well accepted" recommendation of 1.0mm. Would it be ok for me to use it as is?

Some specifics - the cylinder base had been shaved hence the issue. I am already using 1mm stack of base gaskets. I'm putting in ARP rod bolts/nuts, head studs and the car has relatively mild SC cams.

Comments / experience?

thanks.

David 04-09-2006 04:42 AM

That's too tight, go ahead and add a 0.25 gasket.

tom1394racing 04-09-2006 04:00 PM

Check out what happened to Synchroid when he went with 0.5mm deck height.
http://forums.pelicanparts.com/showthread.php?s=&threadid=265554&perpage=20&highl ight=euro%20pistons&pagenumber=2

hobieboy 04-09-2006 06:57 PM

ok - I hear ya guys (& gals)...

My only concern is that I'm already stacking 3 gaskets - 2 0.25mm and a 0.5mm one. If I "shim" it up to 1.25mm, we are talking about "very thick" base gaskets. Will that cause any problems? If I do that, would it be better to get another set of 0.5mm so I'll use 2x0.5mm + 1x0.25mm ones as opposed to 3x0.25mm with the 0.5mm ones?

Carrera3.5L 04-09-2006 07:17 PM

I am running .75mm on my normally aspirated motor with no problem, although I am using RSR style pistons with a mild camshaft profile so I have more than adequate piston-to-valve clearance. We strive for somewhere between .8mm-1.00mm deck height. The tighter clearance may help with detonation issues.

.7mm is getting awfully tight, just to be safe you may wish to add another .25mm shim. If you have 1.00mm worth of base gaskets already, you may also wish to trade in your combinaton of .25mm-.5mm base gaskets for a 1.0mm & .25mm shim. It may lessen the opportunity for a leak later.

If you have the time and are willing to experiment, you can build the long block, time the cams and check your piston-to-valve clearance to see if you have a problem. You may or may not get away with the tight clearance.

At least your smart and checked your deck height, you would be surprised how often this process is overlooked, even by supposed "experienced" engine builders. We sent out quite a few "replacement" Mahle pistons to shops around the country that made this error. You can't assume anything.

Ralph

hobieboy 04-10-2006 03:35 AM

Ralph, any idea where could I get the 1mm base gaskets?

With turbo and the SC cam, I don't think I'll run into piston/valve clearance issues. The cam is pretty mild, but will definitely check.

When I did the top end last time with stock P&Cs, I got 0.9mm deck height and had plenty of piston/valve gap. With everything else in the top end unchanged, I suspect I would be ok if I can get deck height back in the 0.9mm range. Trying to save another dry assembly if I can ;)

Carrera3.5L 04-10-2006 06:11 AM

Quote:

Originally posted by hobieboy
Ralph, any idea where could I get the 1mm base gaskets?

With turbo and the SC cam, I don't think I'll run into piston/valve clearance issues. The cam is pretty mild, but will definitely check.

When I did the top end last time with stock P&Cs, I got 0.9mm deck height and had plenty of piston/valve gap. With everything else in the top end unchanged, I suspect I would be ok if I can get deck height back in the 0.9mm range. Trying to save another dry assembly if I can ;)

I know Andial used to carry them, you can give them a call at 714.957.3900 or better yet, Wrightwood Racing, who imports all of the nice gasket pieces and assembles them in kits to suit your individual needs. Charlie or Rosemary can be reached at 805.385.7191. This is assuming that Pelican doesn't carry them, of course.;)

Ralph

ChrisBennet 04-10-2006 09:08 AM

I think with a low deck height you want to be worrying about the piston to head contact more than valve to piston.
Ralph, Wrightwood only sell wholesale last I knew. Not an option for most of us.
Competition Engineering advertises thicker base gaskets.
-Chris

jbell959 04-10-2006 03:40 PM

Check with Jon over at EBS - I think he has them.

NevenM 04-11-2006 02:11 PM

Hi

how did you measure the Deck Height and what is your valve to piston (which is far more important)

Neven

hobieboy 04-11-2006 05:55 PM

There's a tiny bit of chamford (spelling?) on the cylinders, so I measure the height between top of cylinder and the highest point (i.e. flat part) of that chamford area.

Yes, piston/valve clearance is important and I'll measure it. But, if I keep same deck height and the top end did not change (i.e. head, cam, valve, ...) then theoretically, nothing should change from last rebuild. I'd still measure it but will likely take my chance and really assemble it instead of a dry assemably.

David 04-11-2006 07:07 PM

Measure by glueing a little piece of solder (thin solder) on the edge of two sides of the piston crown, put on the head, and turn the engine over. Then measure the squished solder. You may have more clearance than you think.

P.S. EBS has the thick base gaskets.

NevenM 04-11-2006 07:07 PM

Hi

Quote:

so I measure the height between top of cylinder and the highest point (i.e. flat part) of that chamfered area
This is probably not accurate as you are assuming that the edge of the head protrudes beyond the edge of the cylinder, (and the opposite is probably true) Before adding shims I'd do a "solder crush" reading.

Neven

Porschekid962 04-11-2006 11:49 PM

Kudos for measuring it. As others have said lots of people dont even bother with this step when building a motor and also skip things like cam gear offset. Its funny how you skip things on high priced motor builds. I think your best bet is to measure your height as many times as you are willing to with different methods to get a range and average and go from there. As was said earlier EBS racing sells thicker base gaskets as did/does Andial and some other high end buildiers/shops. The less stacking of gaskets the better for sealing. I havent seen many motors leak from the cylinder bases but I havent been around too many turbo motors. At this point it would really behoove you to go the extra yard and wait a week for an odd sized gasket to show up for the build.

best of luck, cheers!


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