Deck Height

A couple weeks ago I wrote in that I had Low compression in my '77 1000. Since then I did a leak down test and found that the head gasket was leaking and also 1 exhaust valve in #3.
I was asked about cam timing, which was dead on. Also was asked about the deck height. Which I did not know the answer to at the time.
Now I have the engine on the stand tore down and can say that the deck height measures .015 across all cylinders.

So My question is. Is this good or bad? Oh,by the way ,my pistons are stock 70mm wiseco 10.25:1 if that matters.

So if I understand you, the pistons are .015 down in the sleeve?

If this is right then you can install a thinner base gasket (up to .015 thinner) or have your head milled .015 to bring your pistons to .000 (zero) deck height. You can run the pistons out of the hole by a few thousands but don't do it unless you've checked all of your valve to pistons clearances and piston to top of combustion chamber clearances.

Milling your head or installing a thinner base gasket will increase your cranking pressure and compression and fixing the valve in #3 will help overall engine performance.

Good luck,
Buzz

Milling the head will bring the chamber closer to the piston but wouldn't the distance from the piston to the block deck remain the same? And what is the deck height supposed to be with those pistons anyone?

Here is some suggested reading.
We had a thread a few weeks ago titled "piston to head clearance" serval people gave their ideas of the pros & cons. If you can't find that thread, click on my screen name and it is page 9? of my posts. Maybe it will be helpful. It's just a suggestion.

milling the head doesnt affect deck height or quench height(squish) just PTV and cam timing. running a thinner base gasket will affect cam timing aswell. deck height doesnt really matter as long as squish is ok. running thinner or thicker headgaskets or milling the block or head will affect squish. measure what you have, if its too much, run a thinner base gasket or headgasket or mill the block. once that is fine if compression is still low mill the head. make sure you check cam timing, you will need a degree wheel to do it properly

Unless you are planning on doing some racing, there really is not a need to run a zero clearance on the deck.
The main thing to check, is the deck flat and is the head flat, if not then get them milled.
Since you said you have a valve leaking, a valve job for the entire head should be done along with a bench shim.

I Think I'll just leave the deck height alone. No need for any extra machine work. Sounds like a valve job should fix the problem. I just want a good streetable engine. Thanks for the input everyone.

nads.com,

Of course you're right. What I meant to say was either reduce the thickness of the base gasket or mill the cylinder block.

I would still replace the cylinder base gasket (either with a like or thinner gasket) since the head is already off the bike and the seal between the base gasket and the engine block is probably already jeapordized.

Good luck,

Buzz

dshelly wrote:

I Think I'll just leave the deck height alone. No need for any extra machine work. Sounds like a valve job should fix the problem. I just want a good streetable engine. Thanks for the input everyone.

I agree with u here. no need to get fancy .

the only reason u would mill the cyl or head would be to true them or increase compresion or (Cyl only) to improve squish clearance. lower squish clearance improves the burn in the cyl, allowing for more compresion.
If u start to play with this stuf u need a good knowledge of the pros and CONS. u can do serious damage if u make a mistake.

how did u measure the .015" ? did u have the base gasket installed? did u torque the cyl's down using a spacer?
Do u have a history with this bike? is the cly and head stock or have they ever been milled?