Honda TRX250R Forums banner

1 - 20 of 33 Posts

·
Registered
Joined
·
12,886 Posts
Discussion Starter #1
This topic comes up almost weekly, I will attempt to clarify it as much as possible...

Testing UCCR
Let's not worry about MSV (Maximum Squish Velocity) at this time…I would suggest the use of a CoolHead, when using a CoolHead Domes they normally come set at 2-3 degrees higher squish angle than the Dome angle on standard pistons…as long as you keep a Squish of +.040" or greater, your MSV will be in the safe zone with the use of a CoolHead Dome and proper Squish clearance.

Now; let's take the easy way out for measuring UCCR:

Get a small tube of White Grease, small bottle of Marvel Mystery Oil (or any other low viscosity or thin Oil), a plastic graduated syringe from a Pharmacy or Veterinarian (Horse syringe) 100CC capacity (or get two 60CC syringes), a $5 calculator and lots of patience…

· You need to set the engine on the bench, remove the head, gasket and make sure the deck is clean. This can be done with the engine in the chassis (more work), remove plastics, tank, ect…

· Level the top of the cylinder out using a small 6"-8" carpenters level…level in a crisscross direction between the cylinder head studs

· With piston ½" to 1" below TDC; coat the outer edges of the piston against the cylinder wall with White Grease…use a "Q-Tip" to spread evenly all the way around

· Bring piston to TDC…find TDC using your caliper end, the long blade end that slides out as you increase the caliper jaw opening. Set a steel carpenters ruler (thin edge down sitting on top of cylinder), sit the end of the caliper edge on top of the ruler edge, hold against the steel ruler and rest the caliper blade on top of the piston center as you rotate to TDC…find the point the caliper reads the shortest distance…this is TDC.

· With piston at TDC, wipe the excess grease from the edges of the piston & cylinder wall…you want to leave a very small bead of grease sealing the edge of your piston to the sleeve

· Bolt head (with head gasket in place), NO spark plug and tighten down accordingly

· Take your syringe, fill to the 100CC mark…you want to fill to a known measured amount. If using two syringes, make sure you know the amount of oil in each…keep air out of the syringes.

· Take the filled syringe and fill through the spark plug hole up to the bottom most thread (the thread deepest inside the head closes to the Dome bowl looking from the top). Look at how much oil went into the cylinder-head by subtracting the amount of oil left in the syringe from the amount you started with. This is your Volume of Combustion Chamber at TDC…record this number.

· Add ½ a (.50)CC for the spark plug volume

UCCR = Volume of cylinder at BDC + Volume of combustion chamber at TDC divided by Volume of Combustion chamber at TDC)

Volume of Cylinder at BDC is Radius of Bore in MM x Radius of Bore in MM x 3.1416 x stroke in MM divided by 1000 = Volume in CC's

Example: 67MM piston & 72MM stroke: 33.5MM x 33.5MM x 3.1416 x 72MM divided by 1000 = 253.85CC's

Let's say the amount of Oil you measured or inserted into your cylinder/head at TDC with the syringe was 19.5CC's + .50 (spark plug volume) = 20.00CC's

Calculate: 253.85CC + 20CC = 273.85 divided by 20CC = 13.69/1

Your UCCR is 13.69/1

Use full Links:

http://www.sacoriver.net/~red/uccr.html

http://www.torqsoft.net/squish-velocity.html (this one comes from Polonda)

Carlos.
 

·
Registered
Joined
·
4,143 Posts
Very good info. Sticky it please.

Thanks Carlos.
 

·
Registered
Joined
·
12,886 Posts
Discussion Starter #6
Thanks Stew4169...:)

UCCR scares a few away from performing the procedure; hopefully this link helps make it easier.

Carlos.
 

·
Registered
Joined
·
320 Posts
This did help a lot, I will actually do this someday now that I can understand it better.

Just a thought any chance of a walk through vid ever?
 

·
Registered
Joined
·
12,886 Posts
Discussion Starter #8
Yup, however; finding the time is the problem and remembering to have a video camera at hand...I do agree vids would be cool and very helpfull.

Carlos.
 

·
Registered
Joined
·
44 Posts
So, I just did the math on my rebuild, 72.25 piston, stock stroke short rod motor, and I got 11.93 uccr. This is with the numbers on my pro-cross dome, the last 2 numbers are 27, wich from my research, should be a 27cc dome. I'm running 110, so should I go down to a 25cc dome to squeeze some juice out of my motor- Mid ported CT310( previous owner had neil do the porting I believe) 38mm airstyker, radvalve, full Fatty exhaust. A 25cc dome would put me around 12.807 UCCR.
 

·
Registered
Joined
·
12,886 Posts
Discussion Starter #10
Don't trust the numbers on the Dome...they can and are off by 1-2 CC's most of the time, making a significant difference on your UCCR. Take and measure the Dome volume with a flat plate and CC the volume or follow the instructions fully as listed in the UCCR instructions.

Carlos.
 

·
Registered
Joined
·
12,886 Posts
Discussion Starter #14
Yup, stock stroke is 72MM, 75.94MM piston is a 76MM bore.

As far as determining your compression, you need to determine the Squish, Piston Dome Volume and Dome CC's..if determining the Dome CC's using pure math, that would be difficult. The biggest issue I see is determining what the dimensions are in the machined Dome; the radiuss of the cavity, depth, angle, all would need to be known accuratly.

Using the "liquid" method is far easier than using pure math. One option would be to model the Dome & Squish using a CAD or Modeling program, then machining to the exact model. The CAD or Model program would let you see the volume of the Dome, as long as it was machined properly, it would be an accurate method.

Stick with the "liquid" method; perform a full UCCR...much easier and very accurate.

Carlos.
 

·
Registered
Joined
·
12,886 Posts
Discussion Starter #17
Squish or Squish band is the portion nearest the head Dome when the piston is at TDC. On 250R's, normal Squish clearance will be between .040"-.060" (1MM to 1.5MM). For certain applications, Squish clearance can be set as low as .020" (.5MM) or as high as .080" (2MM) or more.

Carlos.
 

·
Registered
Joined
·
1,350 Posts
Alisobob is anything but an idiot. Probably to smart if anything and that's a very tightknit group over there. It's a completely different site over there for sure. Btw I loved the "self smart" trailor park boys video. Those guys really know cr500's. Personally I like carlo's method better, but all I have ever measured was just the compression ratio in psi and never bothered with anything else and probably won't.
 
1 - 20 of 33 Posts
Top