Big bore on crf230?

[dave90]

Okay so blocks are like trucks and cars then, and big bores are bikes

[Yap Yap]

Just to make it clear to dave90, big bore is a way to make the engine displacement bigger. The bore is the diameter of the cylinder, it's enlarged and then you need to get a matching piston. 

It has nothing to do with big block or small block, it has nothing to do with the valves etc.

Edited February 11, 2016 by Yap Yap

[adnohguy]

No substitute for adding more cc's to get more power from a smaller engine, over a wide range (power band) from adding a larger diameter piston.

Especially it the carb, cam, ports and exhaust can support the increase in cc's.

Otherwise the power band will decrease from the higher rpm areas and only increase at the lower rpm's.

[VortecCPI]

No substitute for adding more cc's to get more power from a smaller engine, over a wide range (power band) from adding a larger diameter piston.

Especially it the carb, cam, ports and exhaust can support the increase in cc's.

Otherwise the power band will decrease from the higher rpm areas and only increase at the lower rpm's.

 

Of course this example is loaded but let's consider this.  If a mildly-built air-cooled engine gets about 1 RWHP per 10cc we get this:

• 223cc = 22 RWHP (baseline)
• 233cc = 23 RWHP (+1 RWHP or +4.5%)
• 247cc = 24 RWHP (+2 RWHP or +10.8%)
• 254cc = 25 RWHP (+3 RWHP or +13.9%)
• 270cc = 27 RWHP (+5 RWHP or +21.0%)

Granted the bigger the engine gets the more loss we have in the exhaust/intake/port/valve areas due to pressure drop.  Very generally speaking If a 270cc engine is moving 21% more volume of gas the pressure drop increases 46% due to the square law (2 times velocity = 4 times pressure drop).

 

I left my bore stock because I wanted to do a low-buck build just to see what happened.  If I was going to do it right I would bore leaving just enough for one or two more bores and I would stroke.  I would also address exhaust/intake/port/valve areas to cope with the added gas flow.

 

Forget about peak power; just imagine the increase in broadness of power.

[SteveThe Snakes]

Of course this example is loaded but let's consider this.  If a mildly-built air-cooled engine gets about 1 RWHP per 10cc we get this:

• 223cc = 22 RWHP (baseline)
• 233cc = 23 RWHP (+1 RWHP or +4.5%)
• 247cc = 24 RWHP (+2 RWHP or +10.8%)
• 254cc = 25 RWHP (+3 RWHP or +13.9%)
• 270cc = 27 RWHP (+5 RWHP or +21.0%)

Granted the bigger the engine gets the more loss we have in the exhaust/intake/port/valve areas due to pressure drop.  Very generally speaking If a 270cc engine is moving 21% more volume of gas the pressure drop increases 46% due to the square law (2 times velocity = 4 times pressure drop).

 

I left my bore stock because I wanted to do a low-buck build just to see what happened.  If I was going to do it right I would bore leaving just enough for one or two more bores and I would stroke.  I would also address exhaust/intake/port/valve areas to cope with the added gas flow.

 

Forget about peak power; just imagine the increase in broadness of power.

It's pretty hard to get figures. There is too much dynamic stuff going on in there. Usually the power doesn't happen too well depending on obstructions. When everything is done right there is a much larger power potential than just piecing performance parts.

[teamrude]

I am making some .021  head gaskets for 67mm now.. Makes 1.75cc less volume. Lets just say your 233 (67mm) makes 10-1 now it will go to 10.6. For best result oval your cam sprocket to allow you to get installed center you want. Thinner gasket will slightly "retard" installed center. Ask Adnoh how much difference when cam is properly degreed in. Normal is 2 degrees advanced over stock.

[adnohguy]

I am making some .021 head gaskets for 67mm now.. Makes 1.75cc less volume. Lets just say your 233 (67mm) makes 10-1 now it will go to 10.6. For best result oval your cam sprocket to allow you to get installed center you want. Thinner gasket will slightly "retard" installed center. Ask Adnoh how much difference when cam is properly degreed in. Normal is 2 degrees advanced over stock.

Bumps torque ever so slightly (every little bit helps) similar to using valves that are not dished in the combustion chamber (flat heads) which adds "some" compression, which bumps torque ever so slightly again.

Yes it makes the valve a little more heavy, but if , like me, you don't don't need turn your engine over 8,500 rpm, it doesn't matter.

But, for me 2d of advance holds the cam timing in the sweet spot far longer than "right on the mark".

That way your engine is in a high level of tune far longer, even as your cam chain wears/stretches.... (Causing your cam timing to retard), which causes a loss of torque as the wear progresses.

Yes you need a degree wheel and some dial indicators, but, like I just stated, you need them any way if you want to optimize your tune to what ever rpm you want to optimize your power at. (To the degree)

Plus, if your using Terry Miller oversize custom valves they come with flat surfaces already.

So:

If you run a cam with a lot of lift, it is necessary to sink the valves in the head for clearance on cam overlap.

This lowers compression.

So does a lot of cam overlap.

You see where I'm going now.

Now we have access to thinner Solid copper (reusable) head gaskets you can optimize your compression ratio for free!

(You have to purchase a oversize bore head gasket anyway, correct)?

Now that Terry is here for us, it's reminds me of a small block Chevy (lol) we have lots of options available! Thank you Terry!

These Sleeper bikes rule the single track trails, now more than ever before.

[adnohguy]

Finished my second engine (262cc 13-1 69mm piston and a 70mm Terry Miller stroker) last Monday and went riding most of the day Last Thursday.

Also I installed a SuperTrap on the end of my stock muffler canister with 14 disk's.

Also installed a "Terry Miller" custom grind cam with .380 lift on the intake and a copy of the 89a exhaust lobe with a lift of .368

The key to this cam is 103-104 lobe centers.

Cylinder head ported by Mike Coe on both engines.

Went down 4 sizes on the main jet.

As always:

Blasted it hard during break in with off the shelf 10-40 Chevron conventional through all six gears 8 times WFO.

Then drained oil (very dirty) and filled with my favorite, Motul 300v. All my builds have the very lightest flywheel that I dare to whittle on.

Compared to my recent build (#1):

269cc 69mm (12-5) bore with Terry's 6mm stroker crank (72mm) this one has a Coe cam about the same specs but 108 lobe centers (Terrys custom cam is based on this cam)

The 6mm vibrates slightly at idle but is disappears as soon as you click it into gear and take off. This engine sounds very mean/different at idle and when blipping the throttle. This engine just sounds "all business" and will rev to limiter easily in ALL six gears.

It has a lot of grunt/pull with a very light front end in every gear, first three gears will wheelie all buy it self if you shift while WFO. I have my rear axle in the center of the total adjustment with 15-45 gearing

As stated many times, No Clutch Issues, that problem has been solved.

4mm 262:

No vibration at idle, more calm sounding when the throttle is blipped, smooth as stock once your in gear and moving.

I ran more compression on the 4mm than the 6mm because the longer the stroke (than the stock stroke) the compression is actually higher.

THESE ENGINES LOVE COMPRESSION

THESE ENGINES LOVE LIGHTENED FLYWHEELS AND CRANKSHAFTS.

UNTILL you have both on the same engine, you don't have a clue to what large smiles they can produce for your enjoyment.

NO IT WONT RUN TO HOT! They don't care and in fact, they just love it!

I run exclusively, 100 octane un-leaded California street legal, Sunoco race fuel.

Well over 13-1 compression and they DO NOT DETONATE it's amazing to me, but I'm so happy because it just works!

The 4mm is really fun, not quite as much grunt as the 6mm, but pulls hard with a light front end that will lift the front end in the first three gears if you shift at the torque peak. If you miss it, then lofting with out pulling on the bars is no so automatic.

While the 6mm is truly brutal and obviously always in the meat of the power band, the 4mm is very deceivingly fast, just not as blatant like the 6mm.

Trust me, it's fast and powerful, traction is regularly very hard to find, front end easily lofts over any thing you desire, the next tight trail turn arrives way faster than your ready for, but super fun to ride with out being finicky or out of control. Both pull hard from idle to the limiter. No steps, no serge, no "coming on the pipe"

Progressive but urgent.

One engine is Mr. Jackal and the other is Mr. Hyde

Keep in mind that I'm talking about a 6spd, electric start little "girls" trail bike here, not some CRF505 on Methanol and Nitrous hill shooter drag race bike.

This is one mans opinion and perspective of one of my favorite trail bikes that I have ever owned.

Next project in the Que:

273cc

Stay tuned.

Edited April 3, 2016 by adnohguy

[frickinjim]

I like how the OP was just confused on what "big bore" meant and the thread has turned into a full-on technical discussion, leaving the young lad in the dust.. LOL

 

As stated many times, No Clutch Issues, that problem has been solved.

 

 

I'm interested in how you got your clutch to perform well. I've seen in a couple posts you "did away with the judder plate." or something along those lines. I have a full box of OEM clutch parts ready to refurbish my 230's clutch and would like to do it right this time, maybe without having to resort to extra-ridiculously-stiff-mega springs (which work great but tire the clutch finger out quickly). I'd really appreciate a detailed how-to for your clutch mod!

[VortecCPI]

I like how the OP was just confused on what "big bore" meant and the thread has turned into a full-on technical discussion, leaving the young lad in the dust.. LOL

 

 

I'm interested in how you got your clutch to perform well. I've seen in a couple posts you "did away with the judder plate." or something along those lines. I have a full box of OEM clutch parts ready to refurbish my 230's clutch and would like to do it right this time, maybe without having to resort to extra-ridiculously-stiff-mega springs (which work great but tire the clutch finger out quickly). I'd really appreciate a detailed how-to for your clutch mod!

 

Hey FJ!  I hope all is well with you.  Guy has all your clutch answers fr sure.

[adnohguy]

I like how the OP was just confused on what "big bore" meant and the thread has turned into a full-on technical discussion, leaving the young lad in the dust.. LOL

I'm interested in how you got your clutch to perform well. I've seen in a couple posts you "did away with the judder plate." or something along those lines. I have a full box of OEM clutch parts ready to refurbish my 230's clutch and would like to do it right this time, maybe without having to resort to extra-ridiculously-stiff-mega springs (which work great but tire the clutch finger out quickly). I'd really appreciate a detailed how-to for your clutch mod!

There are stiffer springs, but not made for a 230f.

No one that I'm aware of advertise/sell them anyway.

You don't need stiffer springs anyway unless your pushing at least 30hp+.

If your above 30 RWHP then let me know because I have the answer for you.

Otherwise remove both judder plates and toss them in the round file. Then replace those two plates by adding 1 more OEM fiber plate.

Next add (1) .080 spacer behind each clutch spring.

That's it! Bullet proof.

You can get my favorite spacer easily at any Honda Automobile dealer.

They are a genuine Honda Automobile 14mm engine oil pan drain plug gasket.

No not aftermarket seals (usually) will not work because they are not .080 thick... Typically only .040- .060 thick.

So unless your carrying a caliper into Pep Boys (example) with you, don't go there.

Then:

Lube your clutch cable with a cable lube tool and your clutch lever pivot with some blue grease.

Oh and clean your centrifugal oil filter since your in that area anyway.... It certainly can't hurt. ,

[frickinjim]

Hey FJ!  I hope all is well with you.  Guy has all your clutch answers fr sure.

Just 6 more weeks of class, so things are good! After that, things will be extra good!

 

 

There are stiffer springs, but not made for a 230f.

No one that I'm aware of advertise/sell them anyway.

You don't need stiffer springs anyway unless your pushing at least 30hp+.

If your above 30 RWHP then let me know because I have the answer for you.

Otherwise remove both judder plates and toss them in the round file. Then replace those two plates by adding 1 more OEM fiber plate.

Next add (1) .080 spacer behind each clutch spring.

That's it! Bullet proof.

You can get my favorite spacer easily at any Honda Automobile dealer.

They are a genuine Honda Automobile 14mm engine oil pan drain plug gasket.

No not aftermarket seals (usually) will not work because they are not .080 thick... Typically only .040- .060 thick.

So unless your carrying a caliper into Pep Boys (example) with you, don't go there.

Then:

Lube your clutch cable with a cable lube tool and your clutch lever pivot with some blue grease.

Oh and clean your centrifugal oil filter since your in that area anyway.... It certainly can't hurt. ,

 

Perfect! The springs I've been using are for the XR200R. Barnett brand. I forgot which year. Heybuddy (TT user from WAY back) recommended them to me after using them in his CoeShow build. They work, but the pain is real. 

 

I'll give this approach a try for sure!

[Baja trail Rider]

I have done Adns clutch mod,on my 6mm stroker. It works perfect,I also use easy pull clutch handle.Using Adn mod, Did not make it hard pull. Only thing I do notice,when you let clutch out.Its more abrupt. After you ride it little,you dont notice it anymore. Also agree the 6mm crank,slight more vibration idling. The 6mm crank makes this bike,baby tractor. Im looking forward,to installing .20 head gasket/slotted cam gear.