Big Bore Case Cutter : How-To, Review, And Info (Minarelli, GY6, 139QMB)

[@rcoverhaul9729]

I have a Gy6 and I ran into the same problem so I managed to fix it using shims just like how you did, but yeah, I managed to bore out my case. Thanks for explaining the measurements in the math to this because of that I was able to do my own engine block.

[@Macavellic]

Thank you for showing also what went wrong, very informative channel !

[@49ccscoot]

Sometimes what goes wrong is more important than what goes right. In this case, not a big deal luckily.

[@Baldys_projects]

I just used my Dremel for my 150cc for the 171 BBK a few days ago it was very thin in a few spots but worked out great! Took about 1-2 hours for boring and fitting. Still need a big valve or 4 valve head with a bigger carb and intake and header.

[@hbpgames7592]

NCY makes a great tool without all that headache with the bolts, 150+ dollars but worth it for an accurate cut especially if your like me and modify this regularly.

[@dirtriderz6881]

Great video again! I love when you upload because I can just set your video to play and get tinkering on my moped.

[@49ccscoot]

Thanks man! Go build stuff! :D

[@marksouthworth3984]

Another quality video man, thanks!

[@49ccscoot]

Thank you!

[@seanc.3168]

Damn that is a spotless case.

[@49ccscoot]

A company was liquidating scooter inventory on eBay and I couldn't resist a brand new set of CPI cases. Bought the last they had.

[@doctordapp]

Thank you for showing this tool... I'm building my own right now, looks quite handy to own. And I need it now, so I have to make it 🤣

[@49ccscoot]

It is. This stuff can be done by hand, but I get better results in less time with the tool.

[@doctordapp]

@@49ccscoot Made the tool yesterday from some printer parts I had laying around... Worked like a charm!!! Now my Yamaha RD50MX 65cc cylinder fits inside my zundapp engine cases. Still have to make a footplate to raise it a little, but my trusty 1931 southbend junior lathe does that job like a charm.

[@49ccscoot]

@@doctordapp Very nice!

[@doctordapp]

@@49ccscoot footplate is ready, 10,45 mm as measured. No is the time for milling out the original head and placing an insert made from a top-racing 70cc scooter head inside it.. Then it's time for matching the transfers... Cleaning and then rebuilding the whole engine. If it works as planned, it's a good base for my first diy twin 😋

[@ludditeneaderthal]

Superb, informative vid!

[@49ccscoot]

Thanks!

[@DivergentDroid]

Very interesting. Now that I have learned way more about boring a GY6 than I ever wanted to know, I think I'll just stick to Mods or move to a ready made larger scooter.

[@timdoyle8199]

Thank you and I'm going to reset the timing and valves I had originally set them at .004 but I think I was a little past the T mark into the rectangle box with a line through it I think right above that is a tiny t and then further up (clockwise) is a long hash mark and then an F so it's supposed to be the tiny t right ??

[@vinshanestrickland4179]

Keep up the good contend get sum grub screws for the tool holder

[@John.santos]

Is there any tool to bore the diameter of crankcase to fit bigger crankshaft?

[@49ccscoot]

Nothing available for purchase that I know of. kzbin.info/www/bejne/gXe5iWRurN-qaJo

[@timdoyle8199]

Nice video again, unrelated,, I just installed a 171 CC Big Bore Kit in my 150cc GY6 adjusted the valves Etc runs good and everything. seems like after it heats up though I'm hearing a little bit of chatter little valve noise, after the engine gets hot. any suggestions? Thanks

[@49ccscoot]

You can try 0.002"in/0.003"ex if they're looser than that now. Otherwise, it is normal to hear some noise. Valvetrains aren't silent.

[@SHADOW-bg4mm]

I wonder if the medal expands so much from the heat, that it would damage my engine. I had to cut the hole bigger, it fits now, just has a small tight fit at the very tip end, inner engine walls. It fits the tight end with just wiggling it in. Im gonna open the engine to take out all medal shavings, so while im at it i might as well put thicker gaskets that I'll have to make, shave the inner walls, so its not tight fit at the tip end.

[@49ccscoot]

On some of the really thin cylinder skirts, perhaps it could put enough pressure on them to change clearance if tight enough even at room temperature. Maybe not. Since it's gotta come apart, you might as well go for the fit that you want. It sounds like it's not far off.

[@ryanthethumb]

Do you have to change the ignition timing when boring so big

[@49ccscoot]

No. With stock ignition parts, it works OK. If you were trying to get the best results, then advance requirements could change with bore, stroke, compression and other variables.

[@danilromanov7518]

give a site where you buy cylinder, please

[@49ccscoot]

I got the one used here from Autotech355 on eBay. ScooterTuning.Ca is a good one for scoots as is PartsForScooters.

[@BrendaEM]

It's a shame that the tool did not come with allen/hex grub screws.

After doing this process, we can install a piston with a width of 139qmb how many millimeters

[@49ccscoot]

That would depend how far you want to push it. The largest kit that I know of is 52.4mm. I'm sure you could go bigger if you really wanted to with custom work... but at that point you might as well go GY6 150 unless it's specifically for a racing class.

@@49ccscoot there is a set of 52mm pistons in my engine 52mm wiper outer diameter 55mm i wonder how much I can expand it 56.5 I wonder if I can install a piston

[@49ccscoot]

@ 54.5mm OD cylinders are fairly common. I'd imagine you can go another 1mm all around (2mm total). Not sure if there's a point. I wouldn't do it for a rider. Most cranks don't last that long if you rev a big big bore anyway.

[@benaco46]

Hi. Where can I find the Boring tool? I have been looking wirh not much luck, Thanks un advance.

[@49ccscoot]

amzn.to/2DX8UbZ (affiliate link)

[@noelvidad8594]

How to buy case cutting tools and how much. Thank you

[@superstarjay3564]

Nice quality videos! Great explanation and visuals, keep up the good work! I have a 72cc mina build but at some point i would like to do a stroker build. 🛵💨

[@austinsledge]

Soooo, i'm using a Naraku 52.4mm bore kit on my 139qmb, do i have to do this? It's looking like so.. haven't tried the jug on yet to see if it'll go, but hoping to get some answers before i get too far 😅

[@49ccscoot]

Most likely you'll need to do some clearance work. That kit has a pretty large diameter. Around 54.5mm where it goes into the cases. Some engines do have larger openings stock, so there's a chance that you get lucky, but I wouldn't expect it. A lot of people just use carbide burrs to open the cases up a little for 139QMB kits, but a cutter will likely give you a more symmetrical result.

[@jeffkrauss5582]

Love the video have you found any cheaper

[@49ccscoot]

No specialty tools. You can do it much cheaper with a rotary tool and carbide bur, but the tool makes it more precise and saves time.

[@jeffkrauss5582]

@@49ccscoot when you do that are you putting the new gasket on the case drawing it out then cutting away the lines

[@49ccscoot]

@@jeffkrauss5582 Yeah. Do your best to keep the cut straight as you go in.

[@xavinb8225]

tool for a 157qmj?

[@javierezequielzicaro7244]

Muy bueno tus vídeos. . Y me da la idea para fabricar un sistema parecido..!!

[@49ccscoot]

Gracias. Compártelo si lo haces.

[@rheaevesuico9109]

where we can buy tools like that?

[@49ccscoot]

www.scootertuning.ca/en/product-home-ruckhouse/790097-boring-tool-ncy-54mm-spacing-for-gy6-engine-1000000006548.html

[@rogersocalbeaches5734]

i loved this video and made me think of a video I didnt see you had covered. Have you ever did a comparison video for Performance Cams? I see various cams included in big bore kits and cant seem to get actual data on how these alternative cams acculally perform. I get how they work, but nobody has ever run a gy6150 with a9 cam, vs a10 , vs a11. Have you made a video? I wanted to message you directly, but cant find where I click to send a message direct.. thanks RC

[@49ccscoot]

I have not. I don't even have a 150 anymore. Someday I'll put a cam in the TaoTao 50 though.

[@rogersocalbeaches5734]

90GTVert on the 50cc, was the cam installed solely or part of a big bore kit? Sometimes those kits don’t come with a new head, so just adding a cam seems to have the most options, but I can’t imagine if just adding a cam with out a bigger bore and / or head will improve performance. So what cam did you remove from the 50 and what was the new cam you used? Were there other mods made at the same time?

[@49ccscoot]

Haven't done it yet. Well, I did have a cam on my last 49cc 4T but it was long ago. An NCY "Performance" cam. Definitely helped top end power, but I only tried it with a BBK. I put an A9 from HOCA in my 150, and included lots of specs and issues with it's installation. See the link below if you're interested in that. 49ccscoot.proboards.com/post/228887/thread

[@rogersocalbeaches5734]

I know your not into 150CC bikes but you may know how to disifer some confusion with the part numbers. I am considering installing a 58.8 big bore piston because its supposed to fit with out boring the case, but the parts state compatible with152QMI/157QMJ 4 Stroke , but NOT P152QMI or P157QMJ . I thought the P only means air cooled. Why would that make any difference? If I knew my inner skirt size I wouldn't have to guess, but with out tearing the bike apart I cant say for sure what will fit.

[@49ccscoot]

I think P engines have a different head that may be taller with larger valves and a more aggressive cam with a longer cam chain because of the taller head. Explained by some as basically a performance upgraded version of the standard GY6 head. If you use the stock head and the cylinder heights match yours, seems like it would be fine. Not a bad idea to make sure the valves clear though. Being Chinese, there's also a possibility that it means nothing and they coded it however they felt like.

[@wadebarnes6720]

What's the difference in horsepower CA 171 CC and the 232 next question is is it worth it

[@49ccscoot]

I'm not really a GY6 dude. The 232 can certainly make more power though. If you push to the limits, you are more likely to have reliability issues. A lot of people stick with smaller bores and strokes for day to day use.

[@wadebarnes6720]

Do you have any ideas on the gears in the gearbox that will help from red line my bike we'll run around 6570 but at 50 mile an hour it wants to Red Line I would be cool with the 50 just trying to figure out how not to Redline

[@49ccscoot]

@@wadebarnes6720 I don't pay attention to redline on the tachs on these Chinese scoots. I just run them where they make power. My 150 was hanging out around 7500-9000 all of the time. If you don't care about power and mostly want engine life, then maybe just back off of the throttle. I'd think you should have room to spare cruising at 6600RPM at 50MPH.

[@timdoyle8199]

Got my scooter running decent although I'm wondering if I'm a touch rich I get a little bit of a sporadic sputter at wide open throttle sometimes but not all the time which is weird ?

[@49ccscoot]

Could be. Could be an ignition issue too. If you've done WOT passes to see what jet works best, then either something has changed or there's an ignition problem.

[@timdoyle8199]

Well you were right on my spark plug wire was not holding tight against the spark plug changed out the Boot and also checked the Spade connection terminals at the coil were a little bit sloppy also tighten those up and the combination of it all seems to have solved the problem it was one and or the other...😀

[@divinewind131]

A LC cylinder. Do I think what you think?

[@49ccscoot]

I think 103cc LC. No fancy race stuff. Mostly like what I've had, just LC. Curious to see how it works out.

[@MrSillypoptart]

Can't I do this on a 50cc and put a 61mm bore into it?

[@49ccscoot]

Maybe. Not sure how well you'll get a 61mm bore to fit a 50. That's a really big bore for most 50s.

[@MrSillypoptart]

@@49ccscoot I agree. If the stud spacing is the same I'm going to try but I think its going to be cut very thin hahaha

[@jp6940]

I need some help with my ‘07 Yamaha Zuma 50 2t. I purchased the Malossi variatior and installed the contra spring that came along with it. I’m a bit confused with my weights. I have a technigas silent pro exhaust. I put the 5.6gm weights and it seems to rev high and has a very narrow powerband. Today I put 6gm weights and it seems to be better. The power and seems to have widened. I weigh 135lbs. Would it be wise to order some 6.5gm and 7gm weights to try out or do you think it’s too high? I am local (Salisbury) and have spoken to you before. I wanna ride sometime man.

[@49ccscoot]

Hey. You can try something simple before ordering... kzbin.info/www/bejne/j5yxmaR7e8qKjLM I use aluminum foil regularly for this. Quite simple. Small scales are cheap.

[@Prebugdaddy812]

Would you sell your style case cutter. If so I’m interested

[@49ccscoot]

PartsForScooters imports this one under the Universal Parts brand. The one that I made, I don't wish to sell. Full plans and templates are available for free if you use the links in the description though.

[@craigmatthews3651]

@90gtvert 90gtvert I installed a 90cc kit on my 50cc Kymco agility but I think I have a CVT problem I'm at 10k revs at 30mph and that's my top speed, I have 7.5g rollers, is my clutch not fully engaging or is my belt slipping?

[@49ccscoot]

First, try heavier rollers to make sure it's not just a simple fix. Then check your belt width and condition and look for signs of slipping. kzbin.info/www/bejne/j5yxmaR7e8qKjLM

[@kubi1110]

61qmk?

[@Kampadakis_Junior]

Will this work with a yx 160/150?

[@49ccscoot]

If it matches one of the bolt patterns of the cutter, it may.

[@TheMuskin1]

Rotary Tool? dremel?

[@49ccscoot]

I say "rotary tool" in place of Dremel often. Dremel is a brand, albeit the most popular. I use a Foredom and there are lots of others out there. I guess Dremel is kind of like Kleenex though, where you may want a tissue but many say Kleenex. Semantics. A small tool that spins bits fast. lol

[@ДжонВокер-к5н]

This is 1e40qmb 👍

[@49ccscoot]

Yes.

[@josepeixoto3384]

It's a pity that nobody makes the tool for 20 bucks,that's all it's worth,more or less.

[@49ccscoot]

How many tools do you buy for $20 today?

[@vinshanestrickland4179]

I like your videos but being a master engine builder with 25 yrs under my belt im screaming at the screen ..

[@Surferant666]

Wow you cowboy... No white spirit to help lubricate the aluminium.. and didnt bolt case down. 1/10

[@carlosscotti695]

Ll8

[@SOVEREIGNDesigns]

lol

[@dreadknot2238]

Why so weak? Buy a bore kit that you'll gonna use it once ever in you're life time. Be a man, use a dremel that tool it probably could use 10 thousands different things with it.

[@49ccscoot]

"Be a man" and use an inferior tool? Ha. I've used small rotary tools on lots of cases. Then I got smarter and made the process more repeatable and accurate, aside from being much quicker.

[@jeffgarbaas9278]

He spent too many hours in high school metal shop.

[@49ccscoot]

I wish. We didn't even have metal shop. We had shop, where you could build a piggy bank or a gun rack out of wood.

[@megatshah6292]

What name of this tools ??

[@49ccscoot]

Case boring tool. NCY and SSP-G make them.