Old Guys Simplex moto-peddle bike
- Thread starter indian22
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A 125CG, with the best will in the world, a following wind and appropriate development, will kick out 15-16 bhp at the back wheel on a good day and still be a rideable engine. You might squeeze another 2 out of it, but it would take time, effort and be less useful than a 200 or 223cc variant.
We beat 17 hp ohc engines with one that had fewer numbers but did the work in the right places.
We beat 17 hp ohc engines with one that had fewer numbers but did the work in the right places.
Thanks Ludwig. From your previous posts about the CG 125 I expected as much. I felt my guy was overselling the power numbers even though he's already on the payroll; he's really been wanting to build this motor a bit. Enthusiasm is good but needs a dose of realism taken along side it to cleanse the system. I'm going to let him do it & I hope it will be tractable enough to ride occasionally on the street. Rick C.
Things to be aware of. Skimming the head to raise compression chnges the angle of the pushrods and rocker arms. We had the locknuts under the arms so they wouldn't hit the rocker cover. This adds in with the cam, as the usual way to modify them is to grind meat off the back. That affects the way the followers sit. It's very much suck it and see. A modified cam will give a bit better lift (not really needed with valves that big) and longer duration. It is unlikely to match the timings of the XR200 camshaft profiles though. Or do you have a cam grinder there? 
If you can get good compression by shaving the head, you avoid needing a heavy raised crown piston, which slows acceleration up.
The driven primary gear on the clutch can reasonably be thinned down, it's as big as the XR's.
A really, really smooth transition from the carb size down to the inlet valve is important. Using the twin ports, keep the exhaust pipe diameter down in order to keep the gas speed up. Consider even blanking one off with a dummy and using a conventional diameter pipe on the other side.
Rod lengths, I am told by Smif that it's the same for the CG125,the CB100 all the way up to the XR200, just the stroke differs. If you can find a shorter rod and then chop the barrel down to suit, you should also get better pick up. We had an XL185 crank ready to go in a CB100 bottom end for a square bore & stroke 125, but we never had the need for it after we stopped racing. That would have been something of a shock to the opposition if we'd built it, or perhaps not seeing how well Black Betty had gone.
If you can get good compression by shaving the head, you avoid needing a heavy raised crown piston, which slows acceleration up.The driven primary gear on the clutch can reasonably be thinned down, it's as big as the XR's.
A really, really smooth transition from the carb size down to the inlet valve is important. Using the twin ports, keep the exhaust pipe diameter down in order to keep the gas speed up. Consider even blanking one off with a dummy and using a conventional diameter pipe on the other side.
Rod lengths, I am told by Smif that it's the same for the CG125,the CB100 all the way up to the XR200, just the stroke differs. If you can find a shorter rod and then chop the barrel down to suit, you should also get better pick up. We had an XL185 crank ready to go in a CB100 bottom end for a square bore & stroke 125, but we never had the need for it after we stopped racing. That would have been something of a shock to the opposition if we'd built it, or perhaps not seeing how well Black Betty had gone.
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I saw this single cylinder 2 stroke bike, has 1 carb and two tail pipes from dual exhaust ports.
The switching to 2 exhaust ports on a four stroke by chaining the head also needs other changes to get the two exhaust port head to be compatible yes? Overhead valves need pushrods and so 2 for exhaust 1 for intake? Is it very complicated or are there kits?
I saw this single cylinder 2 stroke bike, has 1 carb and two tail pipes from dual exhaust ports.
The switching to 2 exhaust ports on a four stroke by chaining the head also needs other changes to get the two exhaust port head to be compatible yes? Overhead valves need pushrods and so 2 for exhaust 1 for intake? Is it very complicated or are there kits?
On the CG 125 4 stroke the head change to two exhaust ports is pretty basic stuff: checking clearances of piston& valves to head, rockers to rocker covers etc. simple stuff is all that is necessary. This is a two valve push rod engine one intake valve and one exhaust valve...that is unchanged only the two port head is changed out i.e. one exhaust valve exiting the engine through two separate ports instead of one.
The only reason I'm looking at this is because the original Harley Peashooter OHV vertical push rod race engine was equipped with a two exhaust port head & I think it would definitely aid in adding a vintage look to the engine. I am almost certain that performance will actually drop off by using a two port head. As Ludwig correctly pointed out in his previous post exhaust velocity will almost certainly drop using two ports and on a 4 cycle engine that's not good. Reducing the size (diameter) of the two exhaust pipes will increase the gas speed (equals good) but probably not enough to equal the original one port design. I am hoping to find the two port head has significantly smaller port passages than the one port head, but again I don't think a performance gain is to be found in this swap. Running a single exhaust & blocking off one of the two ports would improve performance some, if both ports on the new head were each equal in size (diameter) to the original single port design, but not an improvement over the stock one port head.
Why offer a 2 port head today if it doesn't aid performance? Maybe 2 exhausts look and sound cool & neophytes think it will run better, marketing...who knows? In the twenties and thirties head flow testing was probably "guesstimating" & not science, but we know that they thought the bike ran better and I'm sure with the exact setup they were using it did, just not something that can't be achieved better by today's engine tech. Anyway we've decided to hot rod the engine a bit to gain some performance that any loss through the 2 port head results in. I hope this helps and doesn't confuse...I am not going into the subject 2 exhaust ports on a two stroke engine (maybe one of the pipes was a dummy) which I'm convinced wouldn't work at all even with mad gas flow science tools & skills and I don't have them! Man I love this forum...Rick C.
Great insights Ludwig & yes cam grinder is available locally. Guns and all necessary tools we have here in Indian Territory even if we don't have indoor toilets. My guys a bit strange but at engine machine work he's a savant without the idiot part so I pretty much let him go after setting parameters which he usually ignores..he pulls his weight and then some!
I've been a fan of square bore & stroke since a teen as well as keeping reciprocating weight low and balanced....I like horsepower that screams & survives it all. Thanks again for the very explicit comments on the CG motors it is helpful and reinforcing in my efforts. I'm not a huge fan of trying to reinvent the wheel, improve yes, complete design change no or anything else that is time tested. Valued information... Rick C.
I've been a fan of square bore & stroke since a teen as well as keeping reciprocating weight low and balanced....I like horsepower that screams & survives it all. Thanks again for the very explicit comments on the CG motors it is helpful and reinforcing in my efforts. I'm not a huge fan of trying to reinvent the wheel, improve yes, complete design change no or anything else that is time tested. Valued information... Rick C.
Unless there is really high revving, the valve train can be left in 
. Lighter pushrods won't help much, as the system keeps their speed low. Kibblewhite springs were used on Smif's own Blue Dog ohc engine and are highly recommended. I can't remember if he used valves from there as well.
Crankcase breathing, one from the top of the cases feeding into a catch bottle or tank, one from the head into the bottle. This does make a difference.
. Lighter pushrods won't help much, as the system keeps their speed low. Kibblewhite springs were used on Smif's own Blue Dog ohc engine and are highly recommended. I can't remember if he used valves from there as well.Crankcase breathing, one from the top of the cases feeding into a catch bottle or tank, one from the head into the bottle. This does make a difference.
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Ludwig you once posted that the CG125 will rev higher but why take it there if it's stopped making power? Low end grunt is already available in quantity! Mid range assist would be nice...just 'cause I like high revs doesn't mean I'll spend any time there.
Case pressure is often overlooked, at the top especially, and I plead guilty to not addressing this on the Simplex Cooper Gator or the Peashooter either...thanks for reminding.
Finally got round to bracing the fork girders & preparing a stainless exhaust hookup...similar to the one I built for the Simplex, but trimmed down allowing about 1.5" more clearance. I'll need another for the 2 port head, but I'll hold up until I have the new head in hand as I'm not 100% positive it will fit at this point, but I'll not know till I try. Brass tubing are material for side mounted rocker rods housing. Rick C.
Case pressure is often overlooked, at the top especially, and I plead guilty to not addressing this on the Simplex Cooper Gator or the Peashooter either...thanks for reminding.
Finally got round to bracing the fork girders & preparing a stainless exhaust hookup...similar to the one I built for the Simplex, but trimmed down allowing about 1.5" more clearance. I'll need another for the 2 port head, but I'll hold up until I have the new head in hand as I'm not 100% positive it will fit at this point, but I'll not know till I try. Brass tubing are material for side mounted rocker rods housing. Rick C.
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Hi Rick,
I Took advice years ago from an older friend. I was being my typical self working as hard and fast as my body and money would allow to restore a car. The only goal was finish it and drive it. My friend asked why I was always in such a hurry, telling me building it is the best part. He always said "enjoy the build". It was good advice. I remind myself of that all the time.
I see you like the Peashooter, too. They are such delicate looking and beautiful machines. More of a flat tracker than a board track racer I guess.
I Took advice years ago from an older friend. I was being my typical self working as hard and fast as my body and money would allow to restore a car. The only goal was finish it and drive it. My friend asked why I was always in such a hurry, telling me building it is the best part. He always said "enjoy the build". It was good advice. I remind myself of that all the time.
I see you like the Peashooter, too. They are such delicate looking and beautiful machines. More of a flat tracker than a board track racer I guess.
Pat It was good advice & now that I'm both old & slow I've no other choice. The journey is the reward.
The Peashooter in racing configuration saw great success on flat tracks here
& short tracks abroad... mid-twenties & thirties post board track heyday era, but retained that great "boardie" profile. Wheelbase was kept short & fork angles/trail pretty vertical & short compared to a road bike or a speedway racer. Bare bones racers, but oh what pretty bones.
My concept is an amateur C class racer look that could have been raced on local tracks weekends and rode to work during the week. The look of the factory team racers on a amateur's budget...brakes and tranny (the road Peashooter's had three speed transmissions, but no race magneto) the best that could be mustered on a small racing budget....kinda like drag racing during the fifties and sixties, run what you drove to the track. Rick C.
The Peashooter in racing configuration saw great success on flat tracks here
& short tracks abroad... mid-twenties & thirties post board track heyday era, but retained that great "boardie" profile. Wheelbase was kept short & fork angles/trail pretty vertical & short compared to a road bike or a speedway racer. Bare bones racers, but oh what pretty bones.
My concept is an amateur C class racer look that could have been raced on local tracks weekends and rode to work during the week. The look of the factory team racers on a amateur's budget...brakes and tranny (the road Peashooter's had three speed transmissions, but no race magneto) the best that could be mustered on a small racing budget....kinda like drag racing during the fifties and sixties, run what you drove to the track. Rick C.
I'm seeing some progress on the "chuckle head" rocker covers & push rod tubes. When completed they will fit either the single exhaust port head or the dual port head. The forward lean of the Honda 125 cc clone really has a similar feel of the "half a Harley" engine profile & the five speed/ engine case represents the blocked off rear jug/case portion of that converted V-twin engine Harley racers used both on the factory teams "peashooter" Keystone frames. As both the vertical single engine and the half V-twin conversion were raced by the HD factory riders during the same era of flat track racing using the same type "Keytsone cradle" on Peashooter frames; I see it as an appropriate though originally unintended profile when coupled with the side tube "chuckle head" rocker covers (Knuckle head like). With this thinking in mind I'll revisit the twin port head concept after it arrives 'cause the "half a Harley" conversions were single port heads. As I said an unintended bit of mental course correction in the build, but using the same basic components & concept.
Safe holiday all. Rick C.
Safe holiday all. Rick C.
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Thanks Ludwig that's a great catch! A blanking plate would lend a touch of authenticity to a "half a Harley" theme "chuckle head" peashooter and take the back case Honda look down a few notches while giving the appearance of a small Harley V-twin heritage.
I'll be working on both side cases as well, left side should be easy to fabricate an early look. The right side cases pose a more difficult problem. The large front motor mount and Keystone cradle coupled with the antique exhaust will also offer a significant alteration of the 1960's Honda design heritage. Large faux vintage air cleaner enclosure will reduce the space behind the motor, but the Mikuni carb won't jibe with the look I'd like to present and I'll give that some thought as well.
Touch of brass added to the "chuckle head rockers... which are not yet the look they will eventually have. Rick C.
I'll be working on both side cases as well, left side should be easy to fabricate an early look. The right side cases pose a more difficult problem. The large front motor mount and Keystone cradle coupled with the antique exhaust will also offer a significant alteration of the 1960's Honda design heritage. Large faux vintage air cleaner enclosure will reduce the space behind the motor, but the Mikuni carb won't jibe with the look I'd like to present and I'll give that some thought as well.
Touch of brass added to the "chuckle head rockers... which are not yet the look they will eventually have. Rick C.
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100% of the materials in the photo were found in my garage and represent about 80% of what will be required to finish the "chuckle head" rocker covers...some of you guys can probably see where I'm going with this. The large diameter brass tubes were left over from a vintage inboard motor launch I restored many years back (wooden) the tubes are nautical scuppers (deck drains). I will need several aluminum solid rods of varying diameters as well and some time to complete this portion of the motor. Rick C.
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Ludwig, I'll get my hat and go with you because I am already standing a few feet away from the bike at the car show while the "experts" are telling everyone who will listen all that they don't know about the bike in great detail and those that do know are marveling at just how Rick pulled it off so well.
Steve.
Steve.
