LANCER wrote on 01/21/08 at 07:57:03:



Don't want to be too anal but for those plucking numbers and running away with them I believe the 0.015 +0.035 = 0.050 not 0.040.  

smokin_blue wrote on 01/21/08 at 09:34:40:


Sorry, that was a typo on my part, it is supposed to be 15 & 25 thou. for a total of 40 thou.

metri wrote on 01/25/08 at 19:49:04:
The mm conversion figure is 39.4 (– actually 39.37 but we’re not to less than a tenth of a thou with bike work!!).  

Skimming 35 thou off the cylinder (without touching the head) will take you to 8.99:1.

Upping the bore to 95mm would give you 8.61:1 if you change nothing else.  Remember that there’s 4mm of free cylinder above the piston, so if you up the bore you also up the unswept cylinder volume and therefore the total compressed volume (chamber + gasket thickness + unswept cylinder volume).

Up the bore to 95mm and skim 40 thou, and you’ll be up to 9.29:1.

Taking metal off the top of the cylinder has greater effect than taking metal off the head, because part of the head at the sides of the chamber is metal to provide squish – the effect of skimming the head is reduced by the percentage of the bore area which faces solid metal rather than open chamber.


To get to 9.5:1 you’ll need to remove 58 thou through a combination of head skim, cylinder skim and gasket thickness.  

I haven’t confirmed the valve to piston clearance on the Savage.  Being a low compression engine (and low revving ie little cam overlap) it may not be a great problem, but don’t bet on that when you’re potentially bringing the valves a full 1.5mm closer!

58 thou is a lot of metal to remove – 1.5mm of slack on both sides of the timing chain – so you’d have an extra 3mm of chain to deal with through the Savage’s already struggling cam chain tensioner.  Re-profiling the tensioner guides will help a little, as will slotting the cam wheel so you can dial in the correct cam lobe timing to compensate for so much chain adjustment, but I think of you go more than about 1mm of skim you’re opening up a real Pandora’s box of problems unless you have a workshop in your own back garden, plenty of machinery in it and a lot of spare time!!

Skimming is a great answer on pushrod engines – just shorten the rods to keep the valvetrain geometry as it should be – but with overhead cams it can get ugly.  If you want to go for anything more than a mild CR increase and thin skim with the Savage you’re going to need a high compression piston.  I’ve looked around and can’t see anybody listing them – I considered ordering up a one-off, but is it worth the cost in terms of dollars per horsepower?

The reason for the 15 thou off the head :  1. to be sure that the head was perfectly flat, & 2. there is a hard limit due to a head/cyl bolt head that is between them & 3. the squish area.

I choose to try the shaving vs a new piston due to the cost of a new piston and cyl... if I were going with a new piston I would also bump it up to the 97mm size and would need to bore the cyl to match AND have the silicone carbide treatment done.
My current cyl has the silicone carbide already and I am not going to just cut that away for a bigger piston, I would use a different cyl for the 97mm piston.

I will likely inspire some of the knowledgable ones to laugh long & hard, but, I gotta ask. How hard would it be to use a piece of heavy glass to put sandpaper on to dress the head down? I know how much time I put into little things that wont begin to repay me with power, this would at least pay back with something tangible.
I GOTTA learn how to do pics, you folks would get a kick outta the way the shop is coming along, sloooow, BUt man, CHEAP!

Hey,, What is the deal with the bolt that limits the head skim to .015? Is it the length of the bolt or is there a bolt head in the way? If it's the head, couldn't it be cut down a bit? Or, is .015 about as far as the head should go anyway?

Reprofiling the chain guides helps some, I guess, but I reprofiled mine when I did the chain, still had 8 mm of tensioner extension with the new chain, kinda irritated me  

If I was gonna do the cylinder & head work I might look at modifying the guides. Instead of just reprofiling, I might look at adding a thickness of good plastic, like a piece of cuttingboard. That stuff is tough & slick, dunno how it would handle the heat, but it would bear a looking at.

Doesnt sound silly to me, no gasket is good stuff.
Re: Plastic, Just reprofiling the guides doesnt seem to be enough to actually "soak up" the slack in the chain, since a new chain, old guides, no skimming anywhere, left me with the tensioner extended 8 mm. I am thinking that the guides could be built up a bit, using a piece of plastic. It would be hazardous, because it might get loose. I can't imagine attaching it without rivets. I would be scared the whole time I was running it, it would require regular inspections till it became obvious it was gonna make it or not. I think the plastic used for cutting boards would be good, unless it wont handle the heat.

KwakNut wrote on 02/07/08 at 13:56:38:

1st plastic behind the guide ain't going to do you a bit good, unless you are referring the front guide.  And this is an idea because you're planning to skim the head.  This will retard the cam timming a bit.  I figured out that .07" chain stretch will give almost 7° retard on the cam.  So .01 equals 1° retard.  How much bulge to counteract that?  Don't know.
2nd reprofiling the rear guide will take up alot of slack if done right.  What he did to reprofile wasn't detailed other than he bent it.  The only issue I have with this is the plastic has shed off a couple of these guides.  Putting a bow in something with molded on plastic in my book is to risky.  Take an old one, strip off the plastic, and replace it with a block of delrin.  Shape it to your hearts content.  There are quite a few bear quality plastics being invented lately, so do some research, go to a plastics distributer, not the guy behind the counter but someone qualified to pick a plastic for you.  Delrin is a common plastic, not what is considered a bearing plastic, but for a chain guide maybe ok.  I doubt the plastic on their is of better quality.