Is anyone not running a base gasket?

[supertrooper90]

hi, i'm in the process of doing a 10.8:1 87mm (416) ross racing piston and had read about not running a base gasket to get the highest compression possible plus other performance benefits. I have seen a little bit of stuff, but nothing in detail and was wondering if theres anything I should look out for. I'm also running the sparks x-1 cam and an xr400 head gasket. Thanks in advance

[togup]

I do not use a base gasket unless I need the piston clearance, just tack it up good with gasket maker and torq it to factory recomendations. Last summer I built a high compression 460 stroker and I actually had to use a .061 aluminum spacer from cometic and a base gasket .

[togup]

Also the xr400 gasket is a great performance option ,the 400ex gasket measures .040 while the xr 400 gasket measures .030 so your compression ratio will be closer to the intended piston ratio.

[supertrooper90]

what effect will it have on cam timing? I'm not looking get an adjustable timing gear, or a degree wheel.

[togup]

none, by useing a thinner gasket your piston just gets closer to the combustion dome in your head forcing the gasses to a tighter space.

[supertrooper90]

i guess the only other question i have is that its a domed piston. it seems like most people have the weisco's which are flat tops. just worried about valve to piston clearance and the guy at ross racing wasnt very much help at all

[F-16Guy]

It won't have much effect on valve timing, so you won't need an adjustable gear. The only issue that worries me is that the oil passage that feeds the valve train goes up through the base gasket, and if you remove it and use yamabond or some other sealer, the squeeze-out could block or restrict that passage and wipe out your top end. The only safe way to do it would be to add an FST style secondary oil cooler that bypasses that section of the oil passage. I would ask the guy at Ross if he can tell you the deck height of the piston, or you could mock it up with your old base gasket. Just temporarily install the piston with no rings and torque down the cylinder, put it at TDC, and measure the deck height. I think you're looking for about 0.025" minimum squish, including the head gasket thickness. The Cometic MLS head gasket is 0.027" (which I think is pretty close to the XR gasket), so if you shoot for a zero deck height, the head gasket should put you where you need to be. Check it first, though, because some pistons are different than others, and depending on your cam, you may also want to clay the top end to see what kind of clearances you have to play with before you make any final decisions.

[supertrooper90]

yeah, the guy at ross racing said this was an old piston# and really didnt have access to much info on it. I think it was more of an unwillingness to help. I ran across something on the ross and je pistons that said with the dome it will be close to the advertised compression ratio. The piston is already in the cylinder and this is just an after thought while im waiting for my head to come back. I just get confused because most of the old posts on running with no base gasket all just talk about the 440's and dont really mention much about the 416 having lower than advertised compression. they also primarily revolve around weisco flat top pistons.
I'm leaning towards just putting it together as is and seeing how well it runs since no matter what it will be better than the stock piston and cam was.

[supertrooper90]

oh and i already checked the piston deck height with a feeler gauge and around the out side of the piston near the cylinder it is in the hole .043. and the piston has a .190 dome on it

[togup]

.043 is stock ,but are you saying that the dome top piston comes up to the top of the cylinder and is measured .043?If so you dont have any thing to worry about

[togup]

F16 Guy hit it right on the head mock it up get some good measurements if your piston is low in the cylinder get it decked to zero. It is irelavent what the manufacturer says the comp. ratio is , its just close only with a zero deck hight will you see accurate comp.ratios from a given piston flat top or dome.

[supertrooper90]

no what im saying is at the top of the piston right around the edge there is a small flat spot maybe 1/16 to 1/8 in wide that is .043 in the hole. the dome starts an 1/8" in from the outside of the piston wall. sorry its kinda hard to explain, I think im making a bigger deal than I have to out of this. I think most of the compression ratio misinformation is with the bigger bore motors. but im still unsure if that .043 in the hole matters since its only a small amount of the piston that is down there thanks guys so the lower part of the top of the piston is .043 and then it has a .190 dome on top of it.

[F-16Guy]

Originally posted by togup
Oh by the way there are no iol passages between the case and the jug only the timing chain hole which is huge
Actually, there is. There is a passage on the right side that runs from the case near where the filter housing is, through the base gasket, and up through the right side of the cylinder. It then passes through the head gasket and into the rocker cover to the reservoir created by the right cam bearing, which forces pressurized oil through the cam journals and lubricates the valve train.

As far as deck height goes, you have 0.043" from the edge of the piston to the top of the cylinder gasket surface, plus you have another 0.027" when you add the gasket for a total of 0.070" of effective deck height. If you have the cylinder decked 0.043" to achieve a zero deck height, when you assemble it with the head gasket you will have the 0.025-0.027" squish band that will more effectively force the air/fuel mixture into the center of the combustion chamber as the piston approaches TDC. That's what you're trying to achieve here; you want that mixture concentrated tightly right over the center of the top of the piston so that you get the most efficient and powerful combustion. The gain in the compression ratio won't be that much. What you gain is a more powerful, efficient combustion stroke, and a cooler running engine.

[supertrooper90]

my piston looks the same as the powroll one here:

http://www.powroll.com/images/PRODUCTS-WEB/00308.jpg

as for the oil passages i figured I could use a wooden dowel in each of the oil passages to make sure they dont get filled with junk. I'm gonna take out that bottom gasket and do the silicone thing and check my clearances when I get my head back.

I have seen people mention they wanna see at least .100 valve to piston clearance is this excessive or pretty realistic? i've also read .080 and as low as .045 but that seems a little to close for my comfort Thanks again for helping me out.

[togup]

sorry F16 guy I deleted that wrong information your absolutely right ,on the right side between the two small jug bolts on the base of jug

[F-16Guy]

Originally posted by supertrooper90
my piston looks the same as the powroll one here:

http://www.powroll.com/images/PRODUCTS-WEB/00308.jpg

as for the oil passages i figured I could use a wooden dowel in each of the oil passages to make sure they dont get filled with junk. I'm gonna take out that bottom gasket and do the silicone thing and check my clearances when I get my head back.

I have seen people mention they wanna see at least .100 valve to piston clearance is this excessive or pretty realistic? i've also read .080 and as low as .045 but that seems a little to close for my comfort Thanks again for helping me out.
The dowel thing is a good idea. As long as that passage is clear, everything else should be fine. I'm not an engine expert, so the proper amount of piston to valve clearance for this particular application is beyond me. A little extra probably wouldn't hurt in case you float a valve or something, but I'm guessing you'll still have more than enough clearance if you just remove the base gasket.

Another idea you might want to consider is to use just one layer of your MLS head gasket if you're not going to be doing any machine work to adjust the deck height. The middle layer is really just a shim, so if you drill out the rivets and use just the top layer, you can raise the deck height even more. Some people have sprayed the single layer of the gasket with high temp BBQ paint or Copper Coat to help seal, but I think Cometic applies a thin layer of Viton rubber to their MLS gaskets, you it should be fine by itself. Something to think about.

[supertrooper90]

I got an email last night from the guy doing my head work, it will be here by Wednesday so i will let you know how i make out. thanks again for the advice.

[F-16Guy]

I just did a little re-reading. I think you want to shoot for about 0.040" squish including gaskets. If you haven't read this, it has lots of good information:

http://www.exriders.com/vbb/showthread.php?s=&threadid=8316&highlight=decked+cylinder

[supertrooper90]

yeah I saw that and actually read most of it, but the part I get confused about is the cam timing, and that this is all 440 based info, plus the only pistons they speak of is weisco and I think ross may have been in there too but that was a custom built piston. that thread is what lead me to starting this thread. Thank you for pointing it out to me though

[F-16Guy]

When you deck the cylinder, run thinner gaskets, or do anything to shorten the distance between the crank and the cam, it puts slack in the cam chain (think of tightening or loosening the chain on a bicycle or motorcycle). The tensioner takes up the slack, but as it does, it rotates the cam counter clockwise (when looking at it from the cam gear side). That little bit of rotation to take up the slack in the chain retards the valve timing since the relationship between the cam and crank have changed. If the tensioner were on the front side of the cam chain, it would advance the valve timing. It's only a tiny a change, and the effect, if you could feel it, would probably be a shift in the power band toward the upper rpm range. If you bought an adjustable cam gear and a degree wheel, you could set the valve timing back to where it was, but I don't think it's worth the money or effort.

[supertrooper90]

thanks, your explanation helped simplify things for me a little. Thats what I was hoping for, is someone to explain things in a more simple manner. If I want some more bottom end later I will get an adjustable gear and a degree wheel, but for now i'm gonna run it how it is since the budgets kind of tight thanks again