|
|
Post by superelbert on Mar 18, 2012 9:32:30 GMT -5
Hi!
My engine is leaking oil from the cylinder head gasket, so I'm in the process of rebuilding wihth a new cylibnder head gasket. Last rebuild, I had the cyllinder head seal-surface machined about 0,1mm. I should have had the cylinder head seal-surface machined as well as this is most likely the cause of the leakage.
Now, does anybody know how much I can safely machine the cylinder without having the pistons hit the head or valves?
Br,
Elbert
|
|
|
|
Post by grizld1 on Mar 18, 2012 10:49:22 GMT -5
0.1 mm.=0.004". If you do the same to the other surface for 0.2 mm. (0.008") total you'll still be good to go with any OEM or OEM-type oversize pistons. If you're using a big-bore setup, the only concern will be squish clearance--clearance between piston edge and combustion cap. If you're using stock rods, you need about .050" there (competition rods let you go closer). Lowering the deck .008" will retard valve timing slightly, moving peak power a little toward higher rpm's, but the effect should be very small; I doubt you'd feel it.
If you're really concerned about these issues (I wouldn't be), use an Athena head gasket. Those are about .012" thicker than OEM gaskets and compress a little more.
|
|
|
|
Post by richard on Mar 18, 2012 16:46:59 GMT -5
|
|
|
|
Post by superelbert on Mar 18, 2012 17:27:44 GMT -5
Thanks for your answer grizld1!
I realise that in posting my question, I failed to provide infromation towards some of the variables you mentioned!
Im running a stock US-model crank with first oversize stock pistons. I've bought the standard Athena gasket set, very nice you've mentioned that the Athena Head-gasket is thicker than stock, that obviously goes in to the equation as well!
All in all, it sounds like I'll be just fine taking of 0,1mm from the cylinders in addition to the 0,1 removed from the head.
Having said that, it would be nice if i could take off more, not so much for increased compression, but more for tightening up the squish-band, something I believe is allways a good improvement in any engine!
As for any increase in compression, as I'm planning to ugrade to fuel injection and digital spartk control (megasquirt), which should give me better margin on detonation due to the improved fine-tining made possible.
|
|
|
|
Post by grizld1 on Mar 20, 2012 23:21:41 GMT -5
With 2nd over Yamaha cast pistons I've dropped the deck up to .030" with no interference issues. If you start going any lower you'll need to take clay impressions at the piston valve pockets, then pull the valves and run solder crushes between piston edges and squish band. Taking crush readings with different combinations of head and base gaskets of different thicknesses can be very informative. If you drop the deck significantly, you'll need to advance the cam timing by moving the camshaft sprocket.
|
|
|
|
Post by superelbert on Apr 9, 2012 9:07:56 GMT -5
Thanks a lot Grizld1! 0.03" translates to about 0.76mm, which gives me ample margin! I skimmed the cyllinder block 0.07mm, more than enough to give me a prefect seal-surface. Looking at the 0.76mm figure, it becomes tempting to skim the head a bit more in o9rder to increase compression slightly and perhaps improve squish action, but on the other hand, I'm not to keen on upsetting the cam-timing so I'll probablyleave it as is for now. I'll be more than happy as long as I get rid of the oil leak!  |
|
|
|
Post by superelbert on Apr 9, 2012 9:12:00 GMT -5
This message was deleted by the original poster.
|
|
