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Thread: CBR TF125 Bucket Racer

  1. #1
    Join Date
    15th August 2011 - 12:25
    Bike
    CBR125TF
    Location
    New Plymouth
    Posts
    19

    CBR TF125 Bucket Racer

    Hi all,

    I've been working on this little project for quite a while now.
    I had been looking for something as a bit of a bucket racer project for a while when my brother ended up with an MC19 CBR250 that he was parting out.
    So I snapped up the rolling frame and then managed to stumble across a cheap TF125 so the project was away.

    This is when the pallet arrived with all the bits.
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  2. #2
    Join Date
    18th May 2007 - 20:23
    Bike
    RG50 and 76 Suzuki GP125 Buckets
    Location
    Auckland
    Posts
    9,963
    .
    Looks Great. ..... Should make a super Bucket. If you want to try your hand at two stroke tuning go here:- https://www.kiwibiker.co.nz/forums/s...tuner/page2000

  3. #3
    Join Date
    25th March 2004 - 17:22
    Bike
    RZ496/Street Triple R/GasGas/ etc etc
    Location
    Wellington. . ok the hutt
    Posts
    17,730
    I've got a thread on TF build as well. If it ever gets finished. Largely just the wiring to finish that I left to the owner. . . Who is electrician. . . We'll he did get the pipe on last week.

    https://www.kiwibiker.co.nz/forums/s...-s-TF125-build
    I've been told. Dreaming`s free.
    Think I'll go, back to sleep.
    Everybody listen, voices in my head
    Everybody listen, do yours say, what mine says?

  4. #4
    Join Date
    15th August 2011 - 12:25
    Bike
    CBR125TF
    Location
    New Plymouth
    Posts
    19
    I've read your thread, looks like a hot little motor! Can't wait to start into that level of development on mine.

    I keep meaning to update this but I'm not very good at adding the photos.

    I've had mine on track now for a couple of months.
    Initially I just got it going as a completely standard TF. I got lucky that the standard rear sprocket on the CBR and the TF front sprocket seems to be pretty spot on for our Taranaki track and current power levels.

    I chopped up the standard TF pipe and made it fit just to get it running, did a couple of club days like that but it was so choked up by the pipe. Then my brother brought a box of parts for a TF185 that he has in another bike and it came with a frankenstein chamber from a CR80. Its huuuge compared to the standard TF one, I made it fir hoping for a quick and easy gain as I'm not in a position to build a proper tuned pipe yet. It pulls brilliantly out of the turns now but won't rev very far.

    Currently I get absolutely creamed by the FXR's in a straight line...

    I ran the bike at Edgecumbe and managed to fit mid field B-Grade which I was stoked with. The track really suited the bike as its very quick in the turns. I couldn't pass very easy as the other bikes would get a gap at the end of all the straights, but once I got through I could hold my position very well.

    I've just added a flat slide carb so I'm hoping to get out to the track for a tuning attempt tomorrow.
    Hopefully I'll learn a thing or two, I don't know anything about squish bands or timing curves at this point so I am just going to start rich and keep an eye on plug colour and head temp. I've brought an old Alfano kart computer to watch the head temp, hopefully I won't kill it!

    Currently saving for an ignitech and working on getting my workshop organised. Then I'll get into building a spare engine I have and start playing around with some machining. Might have to read some books...

  5. #5
    Join Date
    15th August 2011 - 12:25
    Bike
    CBR125TF
    Location
    New Plymouth
    Posts
    19
    Pic from edgecumbe
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  6. #6
    Join Date
    25th March 2004 - 17:22
    Bike
    RZ496/Street Triple R/GasGas/ etc etc
    Location
    Wellington. . ok the hutt
    Posts
    17,730
    Cool. Yeah buy a degree wheel and measure the port timings. They are stupidly stupidly low on exhaust timing especially. Can't see how they would rev much past 7000,rpm, maybe 6.
    I've been told. Dreaming`s free.
    Think I'll go, back to sleep.
    Everybody listen, voices in my head
    Everybody listen, do yours say, what mine says?

  7. #7
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    3,896
    Same with the piston port. All designed for the cow cocky to tootle around the farm. I went 200' exhaust and piston port on my TS100 and it was sweet. I'd go for a bit less now. I also devconned over the reed valve hole to clean up the intake port. The reed valve is purely to give a bit of overrev beyond what the piston port is tuned for(my theory). If the piston port is tuned properly you don't need the reed. I had a generic design Wobbly pipe on it which was pretty good.
    You need a pipe and a MX ignition, or better. As Dave said, measure everything. It might take a whole weekend. Compression is good but only with the right ignition, and get the squish nice and tight.
    It'll drive you crazy doing it but the "zing" is well worth it once sorted.

  8. #8
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
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    Henderson, Waitakere
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    3,896
    Once you get it revving, 10-11,000rpm sort of thing you'll find it vibrates real bad. Like breaking bits off the chassis bad. Again it has been made to be sweet for the farmer. All you need to do to fix it is press a slug of aluminium into one of the holes in each crank wheel. There are 2 holes in each wheel, one in front and one behind the big end pin. Actually the 125 might not like going that high but it might be worth considering the balance if you find it does vibe.

  9. #9
    Join Date
    15th August 2011 - 12:25
    Bike
    CBR125TF
    Location
    New Plymouth
    Posts
    19
    I thought I had better update this project. Its been a while!

    Cosmetically its gone from its beautiful red and black duct tape decals to a tribute to the Superbike hero of my childhood.

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  10. #10
    Join Date
    15th August 2011 - 12:25
    Bike
    CBR125TF
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    New Plymouth
    Posts
    19
    Then I decided it needed to go as fast as it looked, so I read a book and then started cutting things up...

    I'll have to hunt out my notes to remember what I changed the timing to.
    196deg exhaust from memory, which was about a 9mm cut!

    I didn't touch the transfer ports, but spaced the barrel to get the timing where I wanted it.

    The reed block was removed and hole filled up. I had to cut the bottom off the inlet side of the piston to get the inlet timing right. Precision engineered cut with an angle grinder, I couldn't use the lathe as I needed to leave the length on the other side.

    Previously the engine would max out at about 7000rpm on a very good day. After a wee bit of tuning I've got it revving over 11000rpm! (11000 is where I woos out)

    Once you get it revving, 10-11,000rpm sort of thing you'll find it vibrates real bad. Like breaking bits off the chassis bad
    ^ Yes... horrendous vibrations...

    And while I've now got it revving, it still doesn't seem to make enough power to keep up with anyone on the track...

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  11. #11
    Join Date
    15th August 2011 - 12:25
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    CBR125TF
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    New Plymouth
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    19
    So in an effort to extract more power, I've been working on an exhaust for aaaages, but am finally starting to get some progress on it.

    All the pipes I've run so far have been very much "make it fit" designs based on scrap pipes I had lying around.
    This one is scientifically designed around this bike using maximum engineering technology and minimum fabrication skill.

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    I'm also starting to do some planning for another engine rebuild. This time I'll address some things that will be limiting the power.
    - The piston to bore clearance seemed massive
    - The squish was a little larger than I would have liked but limited by how much I could machine off the head and barrel
    - Standard rings etc
    So I'm going to be up for at least a new piston to sort all the above and might look at rod options while I'm at it.

    I'm going to balance the crank to try and sort out the vibration, but I figure there is no point balancing the crank to the original piston and rod, and then changing those out in a couple of months. So I'm at the "do it once, do it right" stage.

  12. #12
    Join Date
    15th August 2011 - 12:25
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    CBR125TF
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    New Plymouth
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    19
    Quote Originally Posted by speedpro View Post
    Once you get it revving, 10-11,000rpm sort of thing you'll find it vibrates real bad. All you need to do to fix it is press a slug of aluminium into one of the holes in each crank wheel. There are 2 holes in each wheel, one in front and one behind the big end pin....
    Was the engine you had with the slugs of aluminium running a standard rod and piston?

    (I'm an engineer so I like to eliminate variables before blindly following other peoples work)

  13. #13
    Join Date
    15th August 2011 - 12:25
    Bike
    CBR125TF
    Location
    New Plymouth
    Posts
    19
    This morning I went over my notes from porting the barrel.

    I raised the barrel 1.5mm
    Raised the exhaust port roof 6.6mm (+ the 1.5mm)
    Lowered the floor of the inlet port 10mm
    Cut the inlet side of the piston skirt 10mm

    This theoretically results in port timings of 195°Ex/128°Tr/185°In, however I haven't checked it with a degree wheel yet.
    Originals were 155.5°Ex/118°Tr (didn't bother to measure inlet because of the reeds).

    As well as taking the 1.5mm back from the top of the barrel, I machined the head about 1.1mm and used a thinner gasket to get from 17.5cc to 13.7cc (8:1CR to 10:1CR - Uncorrected)
    This gave me a squish band of about 1.8mm, which is about 0.8mm higher than I would like it to be.

  14. #14
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
    Location
    Henderson, Waitakere
    Posts
    3,896
    Quote Originally Posted by anglia4 View Post
    Was the engine you had with the slugs of aluminium running a standard rod and piston?

    (I'm an engineer so I like to eliminate variables before blindly following other peoples work)
    Whenever I balanced a bucket engine thee was very little science involved. There are so many variables beyond th4e simple reciprocating mass versus rotating mass that have an effect that it isn't worth being pedantic. I simply knew which way the balance factor needed to go and made an adjustment in that direction.

    Whatever piston/rod combo you go for you are going to need to reduce the balance factor if you rev it above what it was designed for. Just make a change and see how it feels. Your chassis is vastly different to mine so it will react differently to mine.

    One thing I did find that made a big difference was having a real solid front engine mount. My theory was that it stopped the engine getting into resonance as it had to get the whole chassis to resonate, not just the engine.

    You might want to look at RG500 pistons as an option. I used RG400 pistons and they were heaps better. I still changed them every 2 meetings, often reusing the ring. I only ever fitted the top ring.

  15. #15
    Join Date
    12th February 2004 - 10:29
    Bike
    bucket FZR/MB100
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    Henderson, Waitakere
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    3,896
    Trouble with piston ports is if you raise the cylinder you raise the port floor which reduces port timing. My piston ports were the original width at the top and I filed the bottom of each port, but only about 75% of the port width, down until I got the timing I wanted. Unknown to me at the time I was increasing the time/area which was more important. I didn't take the ports down over the full width as I was already having piston reliability issues and I wanted the piston support. I ended up with a "T" shape port arrangement.
    That squish is huge - 1.8mm.
    Angling the transfer ports vertically as per modern practice will be beneficial to the powerband.
    That pipe flange diameter looks huge. The TS100 cylinder exhaust port was way too big. I expect the 125 is the same so don't make it any bigger

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