R6 engine BUILDING

Is there an engine builder in here who would wouldn't mind clarifying something for me?

*a bit of background: I built a few car engines over a decade ago, spec'd out, the whole (waste of money) thing and what not. Now I would like to build the R6 motors for my race team and have some gaps in knowledge I don't know how to fill. Any help would be very welcome!!!! (warning: I might have too many questions!)

The R6 kit manual shows two different squish (piston to cylinder) numbers, one for intake side and one for exhaust side. How are you supposed to account for this while calculating CR? and does this mean that the plane of the piston is technically at an angle relative to the cylinder head deck? My dumb brain is struggling to consolidate how this works.

 

I'm not looking at the manual and some times they are crappy translation to English but could it have said valve to piston clearance? That will change intake to exhaust side.

 

"Squish" is described in the Kit manual as "piston to deck" clearance. PtV is listed as it's own spec here

 

Yes you're on the right track. The head is slightly tilted relative to the piston and the easiest way to account for that is to average the two measured squish values when calculating compression ratio.

 

My interpretation of that has been the Japanese sort of way to publish specs. The squish is different for intake and exhaust sides of the piston if the piston does not rock in the bore. Most builders use solder, the piston rocks in the bore, and the measurements are generally similar between front and rear.

These specs are pretty safe specs, and experienced builders push some of those significantly further into the danger zone in search of more power - be careful with too much compression on the R6.

 

I know it's quite a small amount, but intuitively I was struggling XD Thanks a lot m8!

When you say "too much" does that mean past the "SS" category (listed above as 14.5:1)? Also, I am not quite following how they calculate the 13.1:1, as most formulas I've found and used as is are pointing toward closer to 10.8:1 stock. Variables I'm using are listed below. I've got a build in which I will be measuring all aspects of it (once the heads come back from the machinist) and I will collect the actual numbers for the calculation. But what's confusing me is that I should be coming up with the correct CR with "base" numbers, and since I'm not, that means the formulas I'm using must be incorrect (or the numbers I've sourced are off). There's something being overlooked on my part, I'm sure of it. If anyone can point it out, that'd be great!

Formula:

Swept/Compressed

Compressed = Squish vol + Gasket vol + Piston vol + chamber vol
Swept = Cylinder vol + Gasket vol + Piston vol + Chamber vol
(I assume you don't add squish vol to Swept because cylinder volume already takes that into account?)


Cylinder vol = 149.80 (Bore: 2.64" Stroke: 1.67")
Squish vol = 2.69 (using 0.03" piston to head average)
Gasket vol = 2.42 (using compressed thickness of 0.027")
Piston vol = -1.3 (honestly not sure what stock is and I know this makes a large relative difference in final compression, I'm using the reported forged "stock" piston as I can't find the actual oem number, but with all else the same, this would need to be closer to -4.3 to reach 13.1:1 )
Chamber vol = 11.43 (pulling this one out of a forum. I will measure it myself when I get the head back, but this number is supposedly stock head, unmolested, so I should reach correct CR with it)

 

You'll have better numbers once you have the engine in front of you. It's not uncommon for people to incorporate the gasket volume into the chamber volume and I'm pretty sure the dome is higher than that but I don't remember exactly. I also recommend accepting the metric system if possible as the constant conversion between imperial and metric will create a variance if your resolution is only down to the hundredth.

Stupid question. Those numbers in inches and cubic centimeters or another unit?

 

Should be cc, and yes, I agree the metric system would make everything easier, I work in the field of science (laboratory work) daily and everything is metric. Unfortunately my micrometers don't want to read anything but thousandths of an inch XD

*edit*
if you use a dome vol (piston) of -2.1, which I've seen a couple people list for the R6, and you remove the gasket vol, you actually arrive at 13.2 (which is what the Yamaha oem manual rounds compression up to). That actually works!

 

I appreciate your thorough math, and CR is relevant, but there is a limit on squish that will end up affecting rod bearing life. The stock rods stretch quite a bit. Some 600 engines take tighter squish better than others - the R6 is generally not one of those. If you are using aftermarket rods, the process changes. Trust me, I have built hundreds of R6 engines. Remember that on a motorcycle midrange power makes lap times, not top end, no matter what the track looks like.

 

Yes, I agree 100%. Usable torque is superior to outright top end. I'm not currently building anything absurd, just trying to make sure I calculate resultant CR after milling a some from the head. I know the change will be close to negligible as we aren't expecting anything past 0.005" off, but I want the actual numbers regardless (I can't not have my data!)

Technically the next part I am struggling to understand is that if I have a crank stamped for (main) bearing codes in this manner: 12221, then shouldn't the resulting journal measurements somewhat mimic that trend? Here are the numbers I am getting (inches, again lol darn micrometer):

1: 1.2217
2: 1.2215
3: 1.2214
4: 1.2214
5: 1.2214

 

You can mill more than that off the head without sacrificing PTV clearance and good cam timing numbers, but 0.005" is safe. Make sure someone hasn't already milled it.

Numbers don't lie. If the crank is used, definitely go by what you measure, then just size the bearings for proper oil clearance.

 

It's a brand new crank from Yamaha

 

I always go by bore gauge in assembled rods minus crank journal diameter (after estimating the right bearing color from stamped numbers). Always throw the bolts used for testing away.

 

<--- this is the method I am currently employing (though I will *also* be plastigauging them because I want the data! Can't have enough data!)


I also have 2 cranks each with a single rod bearing failure. The journals are each measuring 0.25 mm smaller in diameter than the rest. I assume they are scrap? Is there a limit to what is salvageable?

 

I like listening to you two experts talk about this stuff, as I don't understand all of it, but it is nice to learn.

Having said that, my dad used to drag race a CBX and lost a couple cranks over the years. His first one was redone by Falicon and they were supposedly really good. Well anyway, a year or so after repair it failed. I asked around and found a place called marine crank shaft. They fixed it up and he continued to drag race with that crank for another 10 years or so.

https://marinecrankshaftinc.com/

 

Yeah I had my squish a touch tight with stock rods. Had a .018" head gasket with 0 deck height. It barked off throttle but at 11k rpm I could hear pistons kissing. Went to a .023" head gasket, lost that immediate bark but .005" can be the difference between all good and oh shit.

 

was that on a dyno??

 

The road dyno, I didnt flog it I was just running up through RPM and I heard odd noise. Came back and took head off and the squish area was clean but no damage. Put the .023" gasket on and noise gone but I did find the limit.

 

So is there an argument which can be made about reducing combustion chamber volume (removing too much from the head) vs increasing CR? Seems like a double edge sword the way you talk about it. Would it not make more sense to run a set up which increase as much low-end torgs as possible, given the R6 naturally has a screaming top end (especially compared to its current competition)? Was just thinking about the specs on the SuperBike build we are planning on for 2027.

 

This may be a bit off the current topic, but what is the target clearance for the main and rod journals? Also, what are the bearing size increments that are available?