How much can the block be decked and still run pump gas?

[Cary]

Hi, all

 

Finishing up the engine swap and now have the old motor out. I want to build this z24 up as a potential turbo motor or just a really good spare.

 

All internals are new. Kid missed a tooth on the timing gear and blew/burned the head gasket. The damage is not as bad as it looks but there is a small noticeable groove between 1 and 2.

 

Will the block take a little shaving/decking?

 

Hmm, guess I gotta go read up on posting pics

[datzenmike]

I don't think a chain can be loose enough to jump a tooth. Never seen it although it can easily be put together this way by mistake. What happens is the Z24 is notorious for blowing the HG at 100K intervals. Not recognizing the gasket has blown and keeping on driving it can cause block and head erosion of the metals from gasses passing through the gap.  

 

You have almost 0.5mm or 0.020" of space above the piston before it is flush with the top of the block or deck. You could safely deck the block 0.020" then. This would raise the compression slightly but not adversly and will move the cam ever so slightly toward the crank and introduce a very small amount of chain slack. Again I doubt enough to be a problem.

 

A competent TIG wender could fill this gap and then have the block decked to only smooth it level. You could probably use a hand held Dremel and do the same.

 

 

While we are at it. You should really check the head for erosion in the same arewa and to see if it is warped.

 

Head and block surfaces must be exceptionally clean and level with bolkt holes in the block clean. Put new gasket on dry, never use dressings. Make sure the two dowels are in the block that align the head properly. Head bolts are totally re-useable if in good shape and lightly oiled.

 

 

To prevent the normal gaske blowing out in the future... At every tune up or once a year, loosen one bolt at a time and tighten to 60 ft lbs. Do this in any order you like but only ONE at a time.

[Cary]

Thanks, head looks good except for carbon but it is going to go to the shop also.

 

I definitely feel like it was an assembly error. I bought it from the kid thinking it was just a timing issue or a bent valve. He and his brother built the motor and when it messed up he was in over his head.

 

If I could get photobucket working I will post pics.

 

[datzenmike]

Stock compression for the Z24 is about 8.26. Decking 0.45mm will only increase it to 8.5 You have tons of room. The Z24 has dual plugs so the timing is only 5 degrees to begin with. The combustion chambers are just short of HEMI shape and very detonation resistant and efficient.

[Cary]

Almost in!

 

[datzenmike]

 

 

 

 

 

 Only gap I see is the hole in the head gasket.

 

However that piston is totally fucked. You can see where the pieces rattled around pitting the piston top.

[Cary]

With it cleaned up there is a small groove between 1 and 2.

 

Piston is pretty isn't she?

[willz]

Take it to a machine shop and ask them how much they'd have to take out of it for it to be flat. Then go from there.

[bananahamuck]

 

 

Ahh that there is one of them new fangled race pistons that let you check your ring gap after installation.

 

 

.

[distributorguy]

Your pistons are at least .020" down the hole, so you have that much room to play with, or even a little more.  The deck is likely not flat anyway.  I bet you find an area that's at least .005" low, besides where the gasket cooked.  You're clearly going to need head work too.  Those marks in the piston are likely worse in the head, right?  A burned valve may have caused the head gasket issue.