Author Topic: Big Bore help (Read 1418 times)

Ciaran · « **on:** October 29, 2012, 12:45:13 pm »

Can someone please explain what a big bore kit is?It is a new/Board cylinder with a bigger piston that increases the cc?

Yuzuha32 · « **Reply #1 on:** October 29, 2012, 12:55:32 pm »

Depends on the machine, in our case it would be a cylinder machined to accept a larger sleeve that increases the usable bore size, along with a piston to match the bore size. this increases the cc's of the machine. ie a 250 to a 285 or 310. carl (iceracer) and gillio have more information and experience on the subject. I will be having a big bore built in the next year or so for MX.

Ciaran · « **Reply #2 on:** October 29, 2012, 01:14:17 pm »

So its Actually the cylinder thats board out?I wasnt sure if it was the sleeve,Im in the middle of rebuilding my bike,But I have a spare cylinder I might get worked on For when my current ones gives out!Can you explain what porting is?

Dezsled · « **Reply #3 on:** October 29, 2012, 01:52:10 pm »

Porting is when an experienced engine tuner using metal cutting/grinding tools reshapes the passageways inside the cylinder (intake and exhaust) to maximize flow at certain or all rpm levels to deliver increased horsepower. Sometimes accompanied by cylinder head modifications for use with premium or higher octane fuels to gain every horse power available.

Think of your engine as a pump, the porting increases the efficiency of the pump for greater output.

Iceracer · « **Reply #4 on:** October 30, 2012, 12:17:45 pm »

A Big bore on a Lt Requires a New Sleeve to be made and machined for the cylinder. You cant get beyond a 70 mm piston in a LT, and at that the ears are very thin.

The other two replies covered the rest pretty well.

Ciaran · « **Reply #5 on:** October 30, 2012, 03:11:22 pm »

How Do i check what bore my sleeve is or my piston?Is it marked on them>?

99Redgtp · « **Reply #6 on:** October 31, 2012, 04:28:53 am »

wiseco pistons used to have a p2, p4, p6, p8 as the last two numbers. it should be smack dab in the middle of the piston crown. the first 3 numbers were either 534 which was 85-86 lt250r, 552 which is 87, or 571 which was 88-92. The letter/number correspoded to the ammount of overbore (ie. pS=stock, p2=.020 over, p4=.040 over, p6= .060 over, p8=.080 over) ive only ever dealt with wiseco pistons so idk what other piston manufacturers use, or if wiseco still uses this number setup or not. you could always get a dial caliper or micrometer and measure the OD of the piston.

Ciaran · « **Reply #7 on:** October 31, 2012, 05:25:54 am »

Quote from: 99Redgtp on October 31, 2012, 04:28:53 am

wiseco pistons used to have a p2, p4, p6, p8 as the last two numbers. it should be smack dab in the middle of the piston crown. the first 3 numbers were either 534 which was 85-86 lt250r, 552 which is 87, or 571 which was 88-92. The letter/number correspoded to the ammount of overbore (ie. pS=stock, p2=.020 over, p4=.040 over, p6= .060 over, p8=.080 over) ive only ever dealt with wiseco pistons so idk what other piston manufacturers use, or if wiseco still uses this number setup or not. you could always get a dial caliper or micrometer and measure the OD of the piston.

I was looking at 'Parts engine' yesterday and I did see Some numbers!I will have to check again! Will a rebore be as simple as getting the sleeve board and putting in the new pistion?

Iceracer · « **Reply #8 on:** October 31, 2012, 08:13:00 am »

Yes if you stay in OEM sizing its pretty much that simple. However once you get up a few sizes in the bores the head should be recut to match.

Ciaran · « **Reply #9 on:** October 31, 2012, 09:45:57 am »

Quote from: Iceracer on October 31, 2012, 08:13:00 am

Yes if you stay in OEM sizing its pretty much that simple. However once you get up a few sizes in the bores the head should be recut to match.

Would does cutting the head involve?
How many sizes up until I have to worry about it?

Best value big bore kit in your eyes?

Iceracer · « **Reply #10 on:** October 31, 2012, 02:38:50 pm »

Best value big bore? This is not a common every day thing. I am about the only one doing them anymore.

Ciaran · « **Reply #11 on:** December 09, 2012, 03:13:32 pm »

Sorry for my delayed response,Been busy with work!

Got my quad finished today!I love it!First time driving it and it scared me silly!

Rainman56 · « **Reply #12 on:** February 10, 2013, 06:04:11 pm »

Just curious how the 310,s hold up as far as the castings being thin.Also is there room for a rebore or is it a one and done as far as rebuilding requiring another sleeve?

Iceracer · « **Reply #13 on:** February 10, 2013, 06:17:36 pm »

There are a 3-4 bores. A good setup will run a couple pistons through each bore if you run enough and good oils, not this 50 or 100 -1 crap for indoor.
Its not cheap to build a big bore Correctly.

Rainman56 · « **Reply #14 on:** February 10, 2013, 06:23:41 pm »

Quote from: Iceracer on February 10, 2013, 06:17:36 pm

There are a 3-4 bores. A good setup will run a couple pistons through each bore if you run enough and good oils, not this 50 or 100 -1 crap for indoor.
Its not cheap to build a big bore Correctly.

I wouldn,t expect it to be cheap.Ya want to play ya gotta pay.Simple as that.

What size carb are guys generally running on the 310,s for MX?

Gillio · « **Reply #15 on:** February 10, 2013, 06:40:13 pm »

Im running a 42.5 carb on my 250 big bore. Once dialed in it runs awesome! BTW I just got home from a race where my 250 ran the fastest it has ever run. Thanks to Iceracer.

LTZ-450 · « **Reply #16 on:** February 10, 2013, 06:52:03 pm »

Quote from: Gillio on February 10, 2013, 06:40:13 pm

Im running a 42.5 carb on my 250 big bore. Once dialed in it runs awesome! BTW I just got home from a race where my 250 ran the fastest it has ever run. Thanks to Iceracer.

what class do you run and how did you do?

Gillio · « **Reply #17 on:** February 10, 2013, 06:58:09 pm »

Im running Quad 250 aka quad 250 2stroke. I'm running ok considering big bore Honda's I run against. Im about 60 laps into tuning and set-up on it. Every week it get faster and handles better.

LTZ-450 · « **Reply #18 on:** February 10, 2013, 07:40:11 pm »

nice. im new on this site and am interested in more info on a big bore for the lt 250r like yours

Iceracer · « **Reply #19 on:** February 10, 2013, 07:41:37 pm »

Ya its coming along good. Big learning curve. Wait till we get to revision L-T4

LTZ-450 · « **Reply #20 on:** February 10, 2013, 07:53:32 pm »

Quote from: Iceracer on February 10, 2013, 07:41:37 pm

Ya its coming along good. Big learning curve. Wait till we get to revision L-T4

are you the engine builder? is this your hobby or business and where are you located. Thanks

Iceracer · « **Reply #21 on:** February 10, 2013, 08:33:03 pm »

Yup, I'm in central New York. It's a little of both. But its not my full time thing, just the other hours Im not sleeping.

LTZ-450 · « **Reply #22 on:** February 10, 2013, 09:14:02 pm »

Quote from: Iceracer on February 10, 2013, 08:33:03 pm

Yup, I'm in central New York. It's a little of both. But its not my full time thing, just the other hours Im not sleeping.

will you be in Lake George this comming weekend if so I my look you up

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Author Topic: Big Bore help (Read 1418 times)

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