Getting close to installing replacement heads on the 327. After a thorough cleaning I’m thinking to use 400 grit sandpaper with a machined steel block to smooth down possible high spots on the block deck. .. Is 400 grit too aggressive?

John

 

If your block is assembled, I wouldn't. If the block is bare, and will be washed with soapy water thoroughly and blown clean with compressed air, 400 would be as coarse as I would go. I would personally not do it. If you have irregularities, better left to a machine shop for a light clean up, avoiding the pad. You'd be amazed at how little grit entering an engine block it takes to cause a LOT of grief.

 

If you plan to use standard head gaskets like the Fel Pro 7733pt there should be no need to sand your block surface.

If you plan to upgrade to an MLS multi layer steel head gasket the block does need to be smoother than factory surface.
For MLS Fel Pro used to teach using a block of machine steel, 100% flat and giving your block 10 to 12 even sweeps with 600 grit to smooth the deck for MLS. Need to be under RA 60 for good MLS life.

 

Yes you can use a flat steel plate to lap. 400 is way too fine maybe 280-320. I did an aluminum race motor once that was together. The sleeves dropped .002-.003". I filled the cylinders with shaving cream and lapped the deck til the sleeves cleaned up. Never gave anymore issues.

 

Use wet or dry with light oil. Will not drop grit. 320 would be better. Wipe cylinder walls with a blue lint free paper towel to clean oil and residue just like you would do to re-ring. Do not use sandpaper, only a quality machinist wet/dry paper like Norton or 3M.

 

I hope for mrg's sake the engine block is bare and on an engine stand if he follows any of the above advice. I've been around, and the returns on 'blowing out' abrasive grit from an assembled engine are slim indeed. But, whatever works for you. Do you guys really use sandpaper/abrasives over open bores/engine lifter valleys?

 

[QUOTE=GTOguy;1602931061

I hope for mrg's sake[/QUOTE]

Translation please?

 

It's mrg's engine?

 

OK. Got it!

 

As I mentioned above, never use sandpaper. Wet or Dry is a different breed altogether. OK to use on an assembled engine as long as you follow instructions above.

 

My comments assumed, never should do that, that this engine would be apart, sand if needed and cleaned properly prior to assembly.
The stock gasket, Fel Pro 7733PT is designed to seal just fine on the factory rough surface.

The sanding I mentioned was only for those that have chosen to run the new MLS head gaskets which demand a smoother surface.
MLS can handle much more pressure than a stock gasket so if you are running a supercharger, Turbo or Nitros MLS is a very good upgrade.
Not necessary for a naturally aspirated fairly stock engine.
If I was to upgrade a stock L79 type, I might consider the 500 series Fel Pro gaskets, they are a little more money but handle more abuse without failure.
In a tweener motor, stronger than stock but not all out race these work really well.
Next step up would be a Performance gasket.
Then the best option for really high performance is the MLS.
The price goes up with each of these steps.
Your gasket thickness options will vary with each step up.
The 500 series are only available in .040 thick.
The stock 7733PT is only available at .039 thickness.
The MLS has several thickness options.
The factory steel shim gasket was thin, .018? Somewhere close to that number.
Aftermarket companies all settled on a thickness of .039 for rebuilt engines assuming the heads might be surfaced or the block decked and the thicker gasket adjusted for this.
There are other companies available also that can provide a quality gasket but I knew and could share the Fel Pro information.

Hope it helps.
Mark

 

Engine in car, the new heads will be installed to replace the current heads. In the past, replacing head gaskets, I’ve had good results with a thorough deck clean and razor blade scraper. Paper towels were in all cylinders and lifter valley wetted with a degreaser to catch debris. .. The thought this time was to also dress the block deck lightly with, as mentioned, wet/dry paper. No intention of using compressed air to blow out debris.

I appreciate all opinions on this. Thanks for chiming in guys.

John

 

I sanded the decks on the aluminum engine because I had to. I was extremely careful about cleanliness. In you case I would use a good scraper then carb clean and reinstall the heads. I wouldn't Sand if there wasn't a real requirement to do so