Simplex 5 speed build

[ndian22]

Bob that's a Bicycle Motor Works head. I've used them on multiple bikes & it's my favorite, though the Fred head and Dax's RT are also great I like the retro style of the BMW head & it's well machined & made in Pa. which makes it about the only made in U.S.A part on most of my bikes...except those I make.

I installed the head on the X-celsior Schwinn this morning & it's now on there permanently. I rode about 20 minutes this a.m. & the performance is better with the new head as well. Without internal mods and an expansion chamber pipe it's performance is not going to ever be in the 40 mph class, but should cruise at 30 no problem.

Speaking of internal mods the new RSE reed valve cylinder is ready to assemble along with the window port piston (another BMW product) the "widow in the piston is 1" diameter, the intake port width is 15/16" & about as wide as is possible without cutting into the threaded stud mounting hole so I'm unsure what effect a full 1" window is supposed to make. I now recall that's the reason I've milled 7/8" widows in my previous reed valve jugs. I bought the piston to test so I'll just test it.   

The two factory transfer ports are enlarged and shaped in both the cylinder and case,as well as matched so the base gasket or gaskets also require trimming to match these ports.

I'll also run a Dellorto clone carb on this reed modified motor and the BMW head, but may have to go to a larger carb setup  later.  RickC

[ndian22]

Expansion pipe with muffler conversion, total length only about 3" longer than the before adding the "can". I will mount this on the Schwinn today.  Rick C.

[pd]

Rick ,

What is the hex at the back of the can ? Is that a cleanout or

Pete .

[ndian22]

I've not removed it but could be. Definitely holds the end cap in place.

[pd]

It looks fairly decent . I don't know why they couldn't have built it to follow 'your' frame better .

Does the muffler do much for your hearing ?

Pete .

[ndian22]

One of the problems of using generic designs to gain a little performance Pete. This expansion pipe design is quite tame in appearance compared to the looping big bulge snake pipes 2 stroke used on many motorcycles...including bicycles. I prefer the short stub for appearance...great performance will dictate if this pipe stays mounted or not.

The muffler completely eliminated the horrible ring ding & roar. I can't begin to describe how bad it was, both deafening & obnoxious to the extreme.  Improved throttle response and  broader power band is evident, but I need some riding time to really decide if it's the pipe or mostly  the other minor changes that are the source of improvement, but it is noticeably improved over the last few days. The final test is when and how pronounced the performance gain, I hope, when it hits on pipe. Rick C. 

[ndian22]

The RSE reed valve motor design (Australian company) developed for the China girl motor. It''s now widely copied. Works well with piston window and or 3rd. transfer port mods. It is often sold as a bolt on power item, but though and unmodified engine will run ok with it mounted, it's just for looks & not for performance increase. Shown with window port piston and modified 3rd. port cylinder.

Reed modified engines require at least up jet or larger carbs tuned to the motor and exhaust. They really breathe & fuel consumption increases dramatically. I'm not a huge fan of really high compression on these engines for the sake of longevity at the least, but small increases are usually of great benefit, especially when coupled with major power mods. Several engine builders have shared that performance is actually degraded with increased compression past a certain modest level.   Rick C.

[pd]

Rick ,

Like everything else in life , there's a balance to be kept . It's just finding the right 'weights' to make that balance happen .

Pete .

[Ricks]

Rick, are the castings as rough in real life as they look in the pictures? I remember sand casting in High School, and they didn't look that bad.

[ndian22]

Some worse than others, Rick. I'd say the cylinders posted here are quite representative of the average. Head & case are ok, cylinders are just rough. Many, including myself have filed the fins  painted and at times refiled the fin edges. Many hrs. of work. The cylinders remind me of the old lawn mower castings of the 1950's. Replacement cylinders are available delivered for about $25. in a couple of days...inexpensive for sure. I'd sure like to see a 100 cc 2 cycle China girl V twin hit the market for a couple hundred bucks!   

Better or worse in photos? I suppose about the same. I still dress up the engine casings  a bit & modify the internals, but now leave the castings pretty much as is. I've had many conversations with and over heard many comments at shows about the bikes I've built & can't recall any negativity about the engines appearance other than questions of how old they are and where do you find the "old" engines and new head. I suppose I should "age" the head to better match the "old"  motor, like I did with the Honda 125 cc clone in my Harley Peashooter, now that one stumps many bike guys in person.   Rick C.

[ndian22]

GT-5 38 mm stroke motor is assembled and installed in my Grubee Sky hawk frame. I wanted to check the engine out with known components in a frame that I'm very tuned to. The primary difference in the two motors is the larger 1" port window cut in the piston & I used thinner base gasket and 4 mm head gasket (compared to .8 mm). The exhaust, RST reed valve, CDI, carb (SHA Dellorto clone), initial jetting (.70) & head are the same as used previously to power the Sky hawk.

I'll run a couple tanks of fuel through her before letting it go rip, but my initial impression is that it sounds & feels pretty stout. It also started right up cold or hot, idled well and was really smooth a low speeds...and showed better low speed manners than the last reed valve China girl engine I built. It is also louder, but it's not offensive.  Rick C.

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[ndian22]

Plug read rich which I expected with riding in town and limiting my short acceleration runs to no more than 5,000 rpm. I'm leaving the .70 jet in till I get some 10 or 15 minute runs completed at more or less constant 6,000 cruising speed. Also I will install an expansion chamber with muffler for testing later & that will lean the mixture quite a bit by itself. I'd be surprised if I need go past .75 jetting even with the expansion chamber or be ok for all around riding with the current .70 in place.  Rick C.

[pd]

Rick ,

What are you using for a tachometer ?

Pete .

[ndian22]

Pete I use a small motor digital combination hour meter tach during break in primarily. I have several and only two currently in use. Run time meter is quite accurate, rpm is too slow to use for say shift points...only use for ballpark engine speed for example stock engine might show 5,500 rpm as pretty easy to reach after break in whereas the motor after modification could show 8,000 as easily and quickly reached. I'm interested in the relative improvement not exact data. Whether I'm at 4,500 rpm or 7,000 actual speed  is not critical, but the differential percent of increase is. One wire hookup, wrap the lead around the spark plug cable & secure in place with zip ties and tape. $15. hard to beat. Mine are all several years old & the non replaceable batteries are still good. Throw aways that serve my purpose.

Rick C.

[pd]

I looked at that type a while back and then again just recently .
The 'new' ones seem to have a replaceable battery , but , from what you say it might be a while before required .

Pete .