Barn Cat - Supercharged CL175

[John Lawrence]

Hi everyone,

This is my build diary of my supercharged 1968 CL175. I am new to land speed racing, so any advice is welcome and encouraged.

BACKGROUND:

   Back in June of this year (2021) a coworker of mine told me he had an old motorcycle in one of his barns that he wanted to scrap, but he would give it to me if I was interested in another project. He knew it was a Honda, it didn?t run, it has no title, but he didn?t have anymore information than that. Later that night he sent me a picture of the bike and it turned out to be a 1968 CL175 (sloper), and it actually looked to be in pretty decent shape for sitting in a barn for God knows how long. I wasn?t sure what I would I do with the bike, but I couldn?t pass up a free motorcycle.

    Once I received the bike, I quickly realized the engine was in rough shape. It was locked up completely. The cam shaft was seized in the head, and the right piston was seized in the cylinder, among some other issues.

   Long story short, since the bike had no title, and it was going to need quite a bit of work to get running, why not do something different with it. After doing some research , I decided it would be cool to build a bike for Bonneville. It looked like the records for supercharged 175cc bikes for few and far between (for modified production). With that, I got to work.

CURRENT STATE OF THE PROJECT:

   As of right now, I am still very early on in the build. I?ve stripped the bike of most of its stock components, and also rebuilt the engine. The engine is bone stock, besides slightly gapped rings. With that said, I plan to only run the bike at around 5 psi to start, but I am fully expecting to run into failures at some point, and learn from them. Believe me I would love to go crazy and do everything under the sun, but time and money are always a factor. I really would like to get it running, and go from there. I don?t want to try to do everything, and never complete the project.

   The plan is to run a draw through supercharger setup. The supercharger I decided to use is an AISIN AMR300. They are fairly cost effective and seem to be readily available if I were ever to need parts or to replace it. In the pictures you can see at this point I have mounted the blower to the bike and designed a belt tensioner. This was the best place I could find to mount the blower without having to do major frame modifications, or run a jackshaft. This mounting spot still gives me room for my legs and it is easy to access. With the current pulleys it should run around 5 psi, but I have other pulleys to adjust that when the need comes.

   I am currently working on the intake system. The plenum is about 80% finished, and I just finished mocking up the tube going from the blower outlet to the plenum. I am just waiting on the tubing and v-band to arrive so I can fabricate it. Once I complete that, I will make the top blower mount that will tie in the top ear of the supercharger to the frame. I wasn?t sure where the intake tube would be, so I waited to do that mount for last.

   As of right now, I am planning on using a Mikuni TM33 (w/ accelerator pump) carburetor. I spoke to a couple small race engine vendors at the recent PRI show in Indy about the project and they both seem to think this would be a good option, but I am open to suggestions.

   The ?tank? that is currently on the bike is just a 3D printed mockup that I designed. I just wanted something there that would give me a sense of where I would be sitting on the bike.


I think that?s it for now. Thanks for reading!

-John

[John Lawrence]

Closer Pic

[Frank06]

Nice looking fabrication work so far.  Have you got the engine to fire at all yet?

[donpearsall]

That looks like it will be a great build. I love the supercharger mount. Very clever to replace the whole case cover with the mount. Keep posting pics of your progress.

Don

[generatorshovel]

 That looks like fun John,,
     You will need a blow off valve, & it's outlet needs to be pointed away from the rider.
I spent 5 years playing with AMR300's ,,,starting with 5-8 lb, but after changing cams to a set more suitable to supercharging (zero overlap) the boost jumped to 10 lb WOW ! what a difference that made 
http://www.dlra.org.au/forum/viewtopic.php?t=1686
Tiny
Down under

[JimL]

Couple things you might already know:

- The small end of the left rod is a trouble thing, on these.  If you find oil soot in the left exhaust header, the piston pin is rocking in the rod.  I have had Honda twin cranks fixed by the marine outboard engine guys.  They fix the rods in position, line bore for oversize pins, and then you bore the pistons to take the slight oversize pins.  Use virgin Teflon rod, machined, to make plugs for the ends of the pins (no circlip).  My original 1969 Speedweek bike was fixed this way in 2007 and runs great again.  I wound up going from a metric pin diameter to inches-based size.

- The aluminum plug in the center of the front side of the cylinders (has the cam chain tension adjustor threaded into it) is prone to coming loose on these old engines.  I had to drill and stake one (use tiny bit and a small knock pin).

- When running this on boost, use a 6V Mini-Trail battery in series to the ignition coil (from your 12V battery).  This will give a good enough spark at high rpm, even if you have some lean spots in your tuning.  This is the same method that was used for the Menard Turbo V6 Buicks in Indy racing, back in the day.

[fissionspeed]

Looking forward to following! I'm jealous, I've always wanted to build a motorcycle but I need to remain married.

[Stainless1]

since you are building your own tank consider something you can rest your chest on to help keep you tucked..... as well as help get your helmet low

[Hoody]

Maybe a daft question? But how much power will be used to spin up the blower? On a small capacity bike like that will the parasitic losses be such that a small turbo would be a better idea than a blower?

[John Lawrence]

Sorry for the late responses, I?ll try to answer everyone:

Nice looking fabrication work so far.  Have you got the engine to fire at all yet?

Thank you! Not yet, but hopefully soon.

That looks like it will be a great build. I love the supercharger mount. Very clever to replace the whole case cover with the mount. Keep posting pics of your progress.

Don

Thank you! It took me some time to land on that design, but it seems to work well so far.

That looks like fun John,,
     You will need a blow off valve, & it's outlet needs to be pointed away from the rider.
I spent 5 years playing with AMR300's ,,,starting with 5-8 lb, but after changing cams to a set more suitable to supercharging (zero overlap) the boost jumped to 10 lb WOW ! what a difference that made 
http://www.dlra.org.au/forum/viewtopic.php?t=1686
Tiny
Down under

Tiny - BOV is next on my list. I plan to use a turbo blow-off valve, without connecting a vacuum reference. I will adjust the spring rate to work for my situation. As far as the cam, did you have one custom ground?

Couple things you might already know:

- The small end of the left rod is a trouble thing, on these.  If you find oil soot in the left exhaust header, the piston pin is rocking in the rod.  I have had Honda twin cranks fixed by the marine outboard engine guys.  They fix the rods in position, line bore for oversize pins, and then you bore the pistons to take the slight oversize pins.  Use virgin Teflon rod, machined, to make plugs for the ends of the pins (no circlip).  My original 1969 Speedweek bike was fixed this way in 2007 and runs great again.  I wound up going from a metric pin diameter to inches-based size.

- The aluminum plug in the center of the front side of the cylinders (has the cam chain tension adjustor threaded into it) is prone to coming loose on these old engines.  I had to drill and stake one (use tiny bit and a small knock pin).

- When running this on boost, use a 6V Mini-Trail battery in series to the ignition coil (from your 12V battery).  This will give a good enough spark at high rpm, even if you have some lean spots in your tuning.  This is the same method that was used for the Menard Turbo V6 Buicks in Indy racing, back in the day.

Jim - I did not know any of this, so thank you for the great info! Do you think the 6V battery will be necessary when running low boost numbers (around 5 psi)?

Looking forward to following! I'm jealous, I've always wanted to build a motorcycle but I need to remain married.

Thanks for following! Luckily my wife knew what she signed on for before we got married lol.

since you are building your own tank consider something you can rest your chest on to help keep you tucked..... as well as help get your helmet low

Good advice. I believe I read in the ECTA rulebook that the tank needs to be 1.35 gallons minimum, but is that the case for running at Bonneville as well?

Maybe a daft question? But how much power will be used to spin up the blower? On a small capacity bike like that will the parasitic losses be such that a small turbo would be a better idea than a blower?

I don?t think that is a daft question, but I don?t know enough about it to know the answer to that. The more experienced guys here could probably answer that though.


Thanks to everyone for all the responses!

[salt27]

since you are building your own tank consider something you can rest your chest on to help keep you tucked..... as well as help get your helmet low

Good advice. I believe I read in the ECTA rulebook that the tank needs to be 1.35 gallons minimum, but is that the case for running at Bonneville as well?

[/quote]


Modified Production SCTA is 1.32 gallons minimum.

I have no idea what AMA and FIM rules are.

I had a CL175 when I was 12, loved that bike.

  Don

[generatorshovel]

"Tiny - BOV is next on my list. I plan to use a turbo blow-off valve, without connecting a vacuum reference. I will adjust the spring rate to work for my situation. As far as the cam, did you have one custom ground?"
No,,,Honda also made a "de tuned" version of the engine called "Hornet", the cams were perfect, they dropped the max HP revs down to a reasonable 15,000 
I re-purposed some valve springs for a BOV

Tiny

[Seldom Seen Slim]

In SCTA bike rules there's a 5 liter limit on fuel capacity in Special Construction, based on the concept that bikes in the class must be not street rideable, if you will, and such a tiny tank would be smaller than even a Sportster rider would tolerate.

I may have oversimplified, but that explanation might help you understand some of the arcane-seeming rules we have.

[TheBaron]

Welcome to the small displacement supercharged group within the LSR community.......

Can't wait to see your bike run at El Mirage and or Bonneville..

Thoughts: the firing of the sparkplugs under-boost can be an issue, however at low boost levels (5 to 7.5 psi) just closing down the the sparkplug gaps to .018"-.020"  can work wonders.

Just measuring off the computer screen the picture of your pulley system looks to spin the blower at about 70% of the crankshaft speed.... That is too much as these blower do move 300cc per rotation.
So two c/s turns means the blower is going to move (300cc X 2) X .70 = 420 and the engine is moving 175cc on its own so 420/175 = 2.4 pressure ratio absolute (which is 21 psi of boost at sea level).

I'd start with about a 1.4-1.5 pressure ratio and your pistons will thank you for it...and pull you ignition timing back a few degrees as well.

Check out My racing partner's blog as there is a lot of info on our bike which runs the same blower that you have....

red-baron-racing.com

Good luck and ask questions if you get stuck.

Robert "Smitty" Smith
Red Baron LSR race team

[stay`tee]

In SCTA bike rules there's a 5 liter limit on fuel capacity in Special Construction, based on the concept that bikes in the class must be not street rideable, if you will, and such a tiny tank would be smaller than even a Sportster rider would tolerate.

I may have oversimplified, but that explanation might help you understand some of the arcane-seeming rules we have.

Where in the current rule book dose it state a 5liter maximum limit for fuel tank in Special Construction ?                   

I note rule 7F in Modified Production states 5liter "minimum" fuel tank limit,,