spirtlanimilbus

im building a 22re late 85-up engine. im curious as to how much decking i will need to do as my block will most definatly need to be decked. ive heard people say that the quench will be messed up if im using an aftermarket piston because they are destroked .003" so im assuming that once i installed that piston with the locked decked .003" my quench would be at factory spec , right? my question is how far above the deck should the piston protrude when the crank is at tdc? ive heard between .005" - .007" but the machine shop says it should be .030" thays a big difference........ ive read a few of engnbldrs posts in other forums but i wasnt able to get a clear definitve answer to this question. does anybody know what the factor spec is ? id just rather not shoot a piston .023" too far up and have a big pile of crap in my garage again...

kyle_22r

don't quote me, but i think engnbldr said .006 above the deck is a good number. i reused the factory pistons on my '91 22RE rebuild(didn't need an overbore, just a hone) and they protruded a little bit.

i think the very safest thing is to find out what the compressed thickness of your head gasket is and work with that. .030 sounds like a pretty big number, i'd definitely check the engine for clearance issues with that.

spirtlanimilbus

Yea No Doubt Kyle, Thanks

I Think If I Get My Block Decked .003" - .004" Ill Be Ok When I Use The Eb Pistons Cuz They Are Destroked .003" That Should Leave The Quench Where It Was From The Factory. (as Long As My Rods Arent Crap....)

engnbldr

>>>*Nearly all aftermarket pistons are destroked by .3mm (about .012"). The reason is that nearly all of these blocks will require at least minimal decking, it has been about a year now since we have seen one that didn't.

*Often a visual inspection will seem to be fine but remember there is something called a "torque wave" created by the loading of the head bolts, so as the engine goes through repeated heat cycles the deck of the block will take a "set". This creates highs and lows, if a small amount it really isn't a concern but at around just .002" up pops future troubles.

Just .002" over the length of the block is nothing, but .002" over a one inch span equals .024" of a 12" length. If it happens to cross the fire ring of the gasket, there will be reduced clamping force in that small area.

*Ever see a head gasket with a tiny break in the fire ring and the rest looks sealed? The weak link is always...well...the weak link.

*Very likely the number two cause of "defective" head gaskets, right behind simple tuning errors.

There are two reason for destroking, the obvious to allow room for decking, and to compensate for compression increase caused by reboring to a larger size.

So if overboring, the small reduction in the piston height puts the compression back close to stock, if you are chasing every single pony then a small gain can be had by combining overboring with decking the block.

My preference is zero deck but up to .006" protrusion is fine. The most important part here is that all four are close to uniform, it is surprising how much difference there can be after a crank is machined and the rods resized.

At this point attention to detail is the difference between running OK and running SWEET!....We always use destroked pistons now....*EB