[GSS]

I finally got around to taking a look at the T20 front sprocket from Hitchcock's that has been residing in my garage for a few months.  I knew some "case modification" was required.  Here are a couple of pictures with the OEM T18 and then the T20 overlaid.  It looks like I will need to grind off about 2 mm from the lower post with the cover alignment dowel.  I don't think this minor modification will have any structural implications so this project looks doable.

However, as I look at the clearance for the chain at the front of the case, that looks pretty close.  I am going to be changing from the OEM chain to one of the Japanese or US made chains and I am wondering if those will fit without rubbing.  Has anyone compared various chains side by side to see which one has the lowest profile?

[Arizoni]

It looks VERY close to me.

The roller in a 530 chain is 10.16mm (.400) diameter so from the bottom of those teeth you will need at least .400 inch to clear them.

That is not the worst part.
The sideplates for a #530 chain have a enlarged area where the diameter is 15mm max (.591) which will also have to clear the housing.

See the following link to see the ANSI G7 Standard Roller Chain dimensions.
Look for the dimension marked "H".

http://tsubaki.eu/chain/ansi-standard-roller-chain/#Single

You will be looking for the RS 50-1 sized chain.

Doing a little math here, from the bottom of the sprocket tooth the outside radius of the side plates will be (.400/2) + (.591/2) = .4955.

Even using this number is dangerous because when the chain is at speed, centripetal force will be throwing the chain links outward, away from the sprockets center.

I wouldn't feel safe without adding at least 1/32" (.032) to the dimension over the outside link to assure clearance with the case.

Adding all of this together, we have .4955 + .032 clearance = .5275" (13.399mm),  minimum measured from the bottom of the tooth to the case wall.

I can't tell by eyeballing but that looks like it might really thin that already thin case wall down quite a bit.
  Only by taking some measurements will you know if the 20 tooth sprocket will work.

Good Luck.

[Hobbydad]

Man, that sprocket is huge. I just put a 19T on my C5, and I thought that was big and a tight fit. Good luck with the project, at least you don't have the kick start shaft to worry about.

[jartist]

You might want to shoot an email to Hitchcock's to see if they've had any experience or advice before you get too radical. Also, try a rev to speed calculator and reference your results to one of the Dyno results posted by others to see where the hp tops out at certain speeds to see if there's a real gain.  I'm thinking a 19good tooth and bigger tires might give you the results you're after.

[ace.cafe]

Personally, I wouldn't do it.
You will be reducing the torque multiplier of the gear train, which will only tax the engine more at all speeds.
This gearing will not help you go any faster. The engine is already too weak for the gearing to make redline in top gear with the stock gearing. It's over-geared with the stock sprocket.
We don't even use a 20T on the Fireball which has almost double the power of the C5.
I don't see any benefit in grinding your engine cases to fit a gear that won't do you any real good. What you need is a stronger engine, not a bigger gear. You have plenty of gear in there already.

That's my 2 cents.

[GSS]

Jim, Ace, Mike, Jartist,
Exactly my thoughts as well. I already have an extremely smooth running bike and will almost certainly lose whatever little torque we have in the top gear....potentially rendering it useless.  Higher speed is absolutely not an expectation, and I will probably take a greater hit as I already have larger tires...4x18 rear and 3.5x19 front.  The 4th gear might gain a bit more usability at >55 mph, but that too is a fairly trivial gain.

This is mostly tinkering driven by intrigue and the fact that I simply happened to buy a T20 many months ago and it has been sitting idle in my garage!  ScooterBob assures me via PM that this has been done successfully by one of our friends in the forum with a little bit of grinding (BTW, can someone get SB to start posting here again?  He is a treasure chest of knowledge for all 2-wheeled things that are "old and European").

Here is a photo with the OEM chain on the T20.  If I grind off a 2mm deep groove in the little post with the alignment dowel, the sprocket will definitely spin freely.  The chain however is extremely close at the front of the case with the clearance being within 1-2mm.

I haven't decided which way I am going to go with this.....possibly back to the OEM T18.  Meanwhile here are two more photographs to mull over!

[gremlin]

I'm guessing it would "self clearance" if you ran it that way.

[ROVERMAN]

Arizoni did the math,i am not smart enough for that. I can tell you you will be courting disaster with that set-up. As others have said,just my 2 cents worth.
Robert.

[barenekd]

I think I lost a couple of miles an hour top speed just going to an 18 T on the G5. On the other hand it cruises a bit faster without the vibration of the 17T. And the mileage has maybe gone up a bit, but not substantially. It does work well for the way I ride it.
The bottom line is this, on the G5, or C5, with stock gearing is probably the best top speed you will see. It's already geared to go in the low 90s. Since it won't go that fast, it's obviously not going to go faster by sticking a larger sprocket on it. The current top speed will be harder to attain as the power at the same speed with the larger sprocket is down a little. Thus reaching the same same original is questionable. Going to a 20T, you'll probably end up being able to go faster in 4th than 5th.
My biggest reason for putting the 18T sprocket on the G5 is the ability to run a quality Oring chain on my bike. If I'd had a C5, I wouldn't have geared it up at all. Believe me, there are no performance advantages, acceleration or top speed wise, with gearing up an Enfield.
If you want to go faster, you're going to need more horsepower, period!
On the other hand, there's a lot of satisfaction to be had when you pass people with your 19 hp, 70 mpg vehicle! You own a win-win situation bike. If you pass the someone, "Hey, you just got blown away by 19 hp!"
If they pass you, "Well, ain't you good, you just passed 19hp! I'm so proud!"
Just yesterday my riding partner and I were riding down Highway 33 toward Ojai and a some guy in a 45O hp Vette caught us and blew around us in short  order, which was fine, but we caught him a few minutes later behind a string of a few Hardly Ablesons. The road was pretty twisty and passing spots were few and far between, but we found the room to get by him and the Hardlys and kept on truckin'. We never saw any of them again! God, I love my Bullet!
Bare

[GSS]

I'm guessing it would "self clearance" if you ran it that way.

I think it will self clearance itself into a self lubricating state inside the crankcase!  Why Hitchcocks would sell this clearly defies logic.

No worries here folks. This was just a quick look at the senseless T20 sprocket. I had already wasted the money and it was fun to take a look to see if it would fit. I think the T18 is just fine with my larger tires.

Meanwhile I might have spotted a tweak for the gear shift mechanism!

[BRADEY]

Meanwhile I might have spotted a tweak for the gear shift mechanism!

GSS, please share this tweak at the earliest !! Hand building on the RE continues for a lifetime, all thanks to all such superb Tweaks.

[GlennF]

My biggest reason for putting the 18T sprocket on the G5 is the ability to run a quality Oring chain on my bike.

I am curious as to the connection between an 18T front and running an O-Ring chain.

Why can't you run a 17T socket with an O-Ring chain ? What is the advantage of 18T ?

[barenekd]

With the 17T sprocket, the wider Oring chain hits the transmission shaft bearing boss. Otherwise, if it weren't for being able to use the quality Oring chain vs the stock no-life chain, I wouldn't have changed the sprocket. Oh, there is another advantage, the vibration points have move up higher into the speed ranges that I don't often use, so the bike is smoother. Very little mileage difference.
Bare
Bare

[The_Rigger]

With the 17T sprocket, the wider Oring chain hits the transmission shaft bearing boss. Otherwise, if it weren't for being able to use the quality Oring chain vs the stock no-life chain, I wouldn't have changed the sprocket.

Is that just in the G5, or also true in the C5?

(Inquiring Noobs want to know...)

[jartist]

C5 comes with an 18t sprocket. If you changed to a 17t you'd have the same issue.