Evo rebuild underway...
#41
#42
#44
Ha just posted in a thread I started about this bearing. I've been fallowing your build and missed this or I could've saved myself some time, I have the same bearing so guess im good.
#45
#47
#49
Squish and compression are two different things. Reducing the space between the D in the head and the piston top .015" will hardly make any increase in the compression at all but will perk up performance. It works by creating more turbulence as it squirts the gases out from between the piston and head which, in turn, causes fuller and better combustion.
Going from a 45 thou to a 30 thou head gasket will decrease the squish 15 thou and then, in addition, you could/should go for a 10 thou base gasket to reduce it even further, that's 25 thou down.
I did this on my own and found that even after doing so, I still had to trim the cylinders another 10 thou, equals 35 total, to get the squish close to considered optimum 30 (it was a few thou above). That is to say, to get the top of the pistons flush with the top of the cylinders so the gap between was determined by the metal gasket.
This means it must have been about 68 thou out of the factory. In addition, the stock compression was well under the 8.5:1 its mean to be. I've heard the squish can be more on some bikes.
Because of the D-shaped head, the cheap and reliably way to increase compression, by reducing the chamber capacity, is by using pistons. I'd say sticking 9.5:1 in will probably get you about a real world 8.5:1 so it's no real risk. I found that by *not* doing so, i.e. by skimming the head and measuring things up.
The truth is, you'd likely end up having to take so much off you'd then start to mess with pushrod lengths, intake angles etc. I think .050 to .070" the limit for skim (without considering and have the tools and skills to do the above). You'll probably only get about .5 a point of compression out of doing so. You cannot trust what the manual/forums says things *ought* to be, e.g. chamber size etc. The only way you know is by measuring everything up, which isn't rocket science and doesn't require expensive equipment.
Still, skimming is cheap to do and not a bad idea, even if just to equalise the height of the heads and get the gasket faces nice and clean and flat. Less hassle than scraping the old paper gaskets off during which you'll probably gouge the surfaces.
The bearing is $10 and so if you have the tools, swop it (I don't have the puller but I have the pusher). From experience, at 40k, if you don't want to repeat all this in 20k, I'd check your rocker arm shafts for wear too. Mine were on the way to the limits.
Does the forum have a tool share system?
Going from a 45 thou to a 30 thou head gasket will decrease the squish 15 thou and then, in addition, you could/should go for a 10 thou base gasket to reduce it even further, that's 25 thou down.
I did this on my own and found that even after doing so, I still had to trim the cylinders another 10 thou, equals 35 total, to get the squish close to considered optimum 30 (it was a few thou above). That is to say, to get the top of the pistons flush with the top of the cylinders so the gap between was determined by the metal gasket.
This means it must have been about 68 thou out of the factory. In addition, the stock compression was well under the 8.5:1 its mean to be. I've heard the squish can be more on some bikes.
Because of the D-shaped head, the cheap and reliably way to increase compression, by reducing the chamber capacity, is by using pistons. I'd say sticking 9.5:1 in will probably get you about a real world 8.5:1 so it's no real risk. I found that by *not* doing so, i.e. by skimming the head and measuring things up.
The truth is, you'd likely end up having to take so much off you'd then start to mess with pushrod lengths, intake angles etc. I think .050 to .070" the limit for skim (without considering and have the tools and skills to do the above). You'll probably only get about .5 a point of compression out of doing so. You cannot trust what the manual/forums says things *ought* to be, e.g. chamber size etc. The only way you know is by measuring everything up, which isn't rocket science and doesn't require expensive equipment.
Still, skimming is cheap to do and not a bad idea, even if just to equalise the height of the heads and get the gasket faces nice and clean and flat. Less hassle than scraping the old paper gaskets off during which you'll probably gouge the surfaces.
The bearing is $10 and so if you have the tools, swop it (I don't have the puller but I have the pusher). From experience, at 40k, if you don't want to repeat all this in 20k, I'd check your rocker arm shafts for wear too. Mine were on the way to the limits.
Does the forum have a tool share system?
#50