What would you do-Deck height clearance?

efhughes3 · efhughes3's Garage

I'm getting ready to start assembly. I checked clearance using the hollow solder method. I got .051" on one side of the piston and about .054" on the other side. Checked it twice and got the same. I've read that 1.25-1.50mm clearance would be best on a stock motor, so I'm right at the low side. But, I'm not too stock anymore, with the 98mm/10.5:1 pistons. I've also got DC19 cams, which have a tiny bit more lift than a 964 grind. I did chamfer the squish ring on the head for a bit more breathing room.

This clearance was with .25mm gaskets, and I did get a set of .5mm from Henry as well, so I could increase my clearance.

Since I've got a few $ going into this beast again, I'd certainly want as much grunt as possible. Am I OK with my clearance, or should I go a bit more conservative with the .5mm gaskets? Maybe the difference is all but insignificant?

Thoughts?

efhughes3 · efhughes3's Garage

The more I study this, the more I've decided to roll with this. It would seem that I'm well within an acceptable deck height. I can help avoid any detonation induced by too much clearance.

PFM · 03-19-2010, 07:45 PM

For what it's worth I would like to know why the clearance is not even front to back. If you are not in a rush I would try another rod or better yet remove the rod and re-install it 180 degrees from where it started. If the rod is bushed / honed a little off this will reverse the clearance. If it does for my money I would have the rods re-worked. If the clearance stays the same the piston or chamber or case deck may need to be looked at.

Stay tuned,

PFM

Steve@Rennsport · 03-19-2010, 07:50 PM

Ed,

PFM offers some really good advice.

I've seen factory rods off as much as .020" center-to-center during the reconditioning process and this is something we really strive to correct. This ensures consistent deck heights and CR in each cylinder. Its a laborious process but well worth the efforts.

Time to do some detective work here.

efhughes3 · efhughes3's Garage

I must not have been clear: There is no uneveness for me to worry about. There is always a bit of difference from side to side. .003" doesn't worry me in the least. There is always going to be some piston "rock". The placement of the solder could account for this much difference from one side of one piston to the other. This is an imperfect check in that aspect.

The rods and case were not split this time, the rods were resized by Ollies when I built it two years ago.