Too many questions!

[relic]

Hello all,
I'll be starting my B+ project later this year, after our riding season ends and in the meantime I've been going through the extra parts that came with my recent purchase. Today I stripped the parts from the spare B+ frame (it had foot pegs welded to it in a trials placement). All this has lead to my having several questions...go figure!
I don't want to be a pest here and I've been trying to research as much as possible on my own to sort out what I've got both in terms of what previous owners have fitted to the B+ I will build and what I've got in boxes. I have a parts book plus this website to look at---a great source of info! (Thanks SH.) When all is said and done I'd like to have an original looking B+ and ride it as a commuter and gravel road fun bike. (my commute is ten miles each way and is back roads for the most part and currently a '76 DT400 does the job)

I guess my first question is what sort of performance can I expect from my B+ ? I have an original shop manual and owners handbook that say that top speed with road sprockets (15 - 36) is 62mph. I imagine that the factory could have been a touch optimistic?

Can these bikes run 50mph without too much trouble?

Can anyone comment on using a smaller driven sprocket as I see 34 and even 32 teeth are available. I know that going with too high gearing often defeats the purpose taking the engine out of its power band.

This is the "spare" B+ in the house before I removed the good parts.

And this is the project B+

thanks everyone! Relic

[Charlie R]

Hi Ken!

I'll drop you a few lines tomorrow. Providing the engine that's in the project bike is in good mechanical working order (I see it's been reed valved) 50 mph should be attainable. I'm gonna spend some time looking over the pics.....

Charlie R.

[Zyx]

I started with a 100B back in 1971. The differences between the B and the B+ were limited to mostly cosmetically functional changes, like lifting the front fender and so on. The core features were the same.

When new, and running on the narrow trials tires that it came with, my B would do around 65 more or less. The speedometer could have been lying to me. Will they go faster? Sure. But it probably isn't worth it.

You ask about using an even smaller driven sprocket than the original, and I assume you are wanting to know if you can eek out a bit more top end. Problem is power, not gearing. The 100B series uses a multi ring piston, modest compression, helical primaries, and an exhaust system that makes adequate power but is not as technical an exhaust as could be made. The carburetor is small, the air cleaner tiny and not an efficient means of passing air, and so on. All together, the result is that it starts to run out of beans around 60. Changing the gears will push the top end up marginally, but there is a point of diminishing returns if all you do is change gearing, because there isn't enough horsepower to turn the taller gearing.

So decide what speed band you really want to ride in. If you are happy with 50 knowing there is more to be had if you need to pass a farm tractor, stock is fine. If you want to do a regular 60 with a margin of error, you will need to modify the power output, and you can do this. It isn't hard to do. But it takes more than one change, such as a different rear sprocket, to make it work. When working well, you are going to get around 10hp at 8,000 rpm or so, and unlike some MX machines, it will not be making lots of extra hp once you get past 7,500.

Folks used to flat track this basic system, so there is a lot of potential in there, much of which is achievable at the cost of maintenance and longevity. Changes that make a difference will generally come in threes, such as changing carburetor, exhaust, and piston, or changing carburetor, head, and piston. This is just like hot rodding a car. No magic bullets, no simple bolt on cure. Everything needs to be thought out.

Someone on this forum will have tried most anything you can think of, so ask question. Don't be shy. You can build a stone stock bike, or a commuter sleeper. Your choice. Modifying Hodakas is a time honored tradition. We have all been doing it for more than 40 years, so have fun. Just map out where you want to go.

[relic]

Thanks Charlie and Arizona. I appreciate you sharing your experience.
At this point I have no idea what shape the engine is in. When I get started on the project I'll be taking it apart and depending on what I find I'll go from there. Amongst the extra parts there is a nearly complete 100cc bottom end, crankcases, trans, crank, connecting rod. Again I don't know much about its condition other than---the rod big end is good. There is some rust/pitting on the crank taper (mag side) where the seal rides.
There is also three 100cc cylinders---one appears to have been modded for reed valve? I'll attach a pic and perhaps you guys can correct me?
A second is scored pretty bad and I haven't measured it to see if its scrap or could be taken another oversize. And the third appears to be original size and in good condition. Again, I haven't measured it.
Also, a new in the box Wiseco 100cc piston and ring. Plus other pistons that I haven't identified yet. I know a couple are tagged "new 125cc" and carry the part number for a Wombat. (From what I read, these are different from the CW piston and if this is true I probably have no need for them.)

note the fin removal by drill bit and the taper at the top of the intake ports

Plus a complete carb and reed valve intake in a coffee can marked "100MX" both look like they've never been used.
I think one of the previous owners was working to convert this B+ to a motocrosser.

Regarding speed--- many of my local roads are posted 80kph (50mph) and the ability to cruise at or slightly above 50 would open up a lot of territory for me to ride this bike. In the past I rescued a Yami Trailmaster 100 and was a little disappointed at the lack of performance. GPS top speed, down hill, laying on the tank was 47mph. The bike served its intended purpose as I rode it in our vintage bike club's "Tiddler" ride that summer but I never plated and insured it since as its use is so limited.

thanks again for all the knowledge sharing and help!

Relic

[Zyx]

Looks like a reed conversion to me. The drill bit thing was crude, but a Dremel will clean that up.

My 125 MX Super Combat powered bike will do 62mph by GPS, and if I put road sprockets on it I would probably get hurt. But it also turns close to 10,000 rpm and pulls like a train. Getting a 100 to do that is possible, but will make it hard to ride around town. Stick to modest. You can get a lot of usable power without crazy rpm. I rode my 100B around Southern Illinois back in the 70's and 55 to 60 was normal.

[Charlie R]

Ken,

That looks like a 2 bolt Model 93 Super Rat cylinder that has been modified for reeds. Nice!

Charlie R,

[relic]

Looks like a reed conversion to me. The drill bit thing was crude, but a Dremel will clean that up.

My 125 MX Super Combat powered bike will do 62mph by GPS, and if I put road sprockets on it I would probably get hurt. But it also turns close to 10,000 rpm and pulls like a train. Getting a 100 to do that is possible, but will make it hard to ride around town. Stick to modest. You can get a lot of usable power without crazy rpm. I rode my 100B around Southern Illinois back in the 70's and 55 to 60 was normal.

Exactly what I would be looking for! If I can cruise at 50-55 without hurting the reliability I will be very happy.

Relic

[Zyx]

Using the reed ported cylinder and a 24mm Mikuni should do it. Stock exhaust isn't all that bad. Upgrade the air filter. Should be good for your target speed.

[relic]

Using the reed ported cylinder and a 24mm Mikuni should do it. Stock exhaust isn't all that bad. Upgrade the air filter. Should be good for your target speed.

I have the 24mm carb and the reed valve intake. Using a vernier I measure my reed ported cylinder to be 51mm. (I'll bring my bore gauge and mic home from work tomorrow and confirm this & check taper and out of round).
I also have a head part # 922501 which I believe is for a 92C?
All of this is in my extra parts---(I've yet to delve into the original engine in my frame.)

This leads me to ask four more questions---(let me know when I'm at my limit... )

Is the cyl hd useable for this application?

Am I a piston away from having everything I need to build a reed valve engine?

Does anyone sell the proper piston or do I need to buy a stock B+ (oversize) and cut the ports myself?

How less reliable would this set up be for a bike that will spend most of its time running 30-50mph with some extended 55mph rides?
(I realize this question is a crap shoot but just generally speaking for my purpose is it a reasonable trade off?)

thanks!

Relic

[relic]

Some further info--- I measured the reed cylinder and its about 51.45mm so close to .060" oversize. And closer inspection shows it is in fact stamped with "+60". There was a damaged piston in with all the parts and I dug that out for a look. It too is stamped .060 and fits snugly in the cylinder. I measured clearance at .002" so on the tight side. (perhaps this lead to the seizure?
This cylinder is well within limits for taper and out of round so I think if I can find a .060 oversize piston and give the cyl a few passes with the rigid hone it maybe useable.

I'm guessing that for 060 oversize my only choice will be Wiseco?

thanks all!

Relic

[Zyx]

Don't know if +60 pistons are still out there. I thought +40 was the limit.

But with regard to that piston, is it really damaged, or only scuffed from a seizure, and what shape is the cylinder wall in? If it is light scuffing and the ring is good, you could reuse it, or at least try it. Not much to lose.

As for options, you can always nickel silicon carbide coat the cylinder, and at that point, you are back in the standard range of pistons with a full choice.

For your intended use, I would think Wiseco or stock 100B, cut for reed, would be better than the rat piston you have.

The seizure could have been caused by lots of things, but if the damage is superficial, a light sanding and back in service. Two thousandths is not overly tight nor is it too loose. Depends on which piston you use. The rat piston with the top Dykes ring can be set to one to one and a half, so two is in the hunt for a used piston.

I think you are potentially close to trying it out with what you have.

[hodakamax]

Relic, I'd check with Paul at SH. I see he has up to +.070 pistons but you might have to make your own holes. As for the +60 stamped on the cylinder, it's just a manufacturing number and has nothing to do with the present bore. I think I'm with AZ on trying the old piston first. Check for cracks around the holes and lightly sand off the scuffs. It should work.

Max

OK, a little edit here. After looking at your picture of your seized piston, it appears to be an old style Wiseco. I can tell by the thickness of the skirt. Early Wiseco pistons were not oval ground as they are today. Measure the piston diameter near the pin front to back and side to side and compare it to a Hodaka piston. You will see that the Hodaka piston is oval by a few thousandths and Wiseco will probably be round. This led to seizures with early Wiseco pistons. The new Wiseco pistons are great. After looking at your situation I would NOT use the old piston. Strangely, I have that same +.060 Wiseco piston on my desk as a paperweight. It had also seized. I measured it and indeed that was the case. I'm glad I caught that!

[Zyx]

Whether the stamping on the cylinder/ head gasket area refers to overbore depends on who did the over bore, or if the parts are old stock replacements. Many machine shops will mark the cylinder with the overbore in thousandths. I have two of them so marked. However, I also have one marked "+3" that is in fact standard bore, along with a standard piston with an ink stamp "3" on it. These later marks appear to be factory, not aftermarket work, so I am led to think that the "+3" and "3" markings are replacement Hodaka parts, not parts from a running bike, and are marked for tolerance. That is, if you buy a NOS or new cylinder from Hodaka ( way back when) it would be standard bore, but we also know bores are lapped to fit pistons so what do you do? Mark piston and cylinder with range references so you can match a piston and cylinder off the shelf and have them ready to use without a full rebore. Buy a "3" cylinder and buy a "3" piston to go with it, and you are very close to being ready to install. I can't think of any other reason the cylinder and piston I have would have such markings, match so closely, and be standard bore.

[Zyx]

As for your piston, the photo is a bit fuzzy, and I took the single ring style to be stock dykes ring Hodaka. Could well be a Wiseco, but I think it would be marked as such, and the ring would be a standard rectangular cross section ring. I have heard of problems with early Wiseco, but only hearsay, and Max could well be right. But, the degree of roundness or oval cross section and the need for it depends entirely on metallurgy. Aluminum of varying thickness expands differentiially. Pistons are also subjected to varying amount of heat across the piston, all of which results in a piston, heated to full operating temperature, that may or may not really be round, which is why most pistons are not round to start with, and frankly are not round when running. Fortunately, it is more important that the ring be round than the piston. At some point in setting clearance, you will have enough to accommodate the piston round or not. So it may be that early Wiseco Pistons, if clearance was set at the front to back skirt, would be too tight. So open it up one thousandth. As long as the ring is still sealing it should be serviceable. The worst that will happen is it will seize again.

Personally, I would try what you have. If it doesn't work out you can always go to plan B. Or, buy a new piston of your choice and send it and the cylinder out to be plated, and let the machinist set it up for you. Up to you.

[hodakamax]

Early Wiseco pistons were not brand marked. They did have a dykes ring at least on this model. The inside crown was marked H100 in the casting. Hodaka did not make a .060 piston at least to my knowledge. The one shown here was ordered by me when they were first were offered. The few that we tried with our clearances of the day all seized. I don't remember who informed us, perhaps Harry Taylor or even Ed about the problem of round Wiseco Pistons. I weighed the stock Hodaka piston which was about 3 ozs compared to the Wiseco at 4 ozs. Notice how thick the skirt is on the Wiseco. The piston in relics picture is almost certainly one of them. I suspect that's what caused the original seizure and I personally would not recommend re-using it.

Max

PS--I should repeat that Wiseco pistons of today are great and that's what I'm using.

[relic]

Thanks for all the info.
Max, you are absolutely correct. This piston is as round as I can measure, has "H100" stamped under the crown and on a cheap kitchen scale, weighs 4 ounces.
So I've got some decisions to make. I don't see a .060" on Paul's site either but they are available. I googled and found a seller who has them listed as "reproduction", no brand noted. When I'm ready to order my other needed engine parts I'll inquire with Paul to see if he has something. I'll need bearings, seals, some hardware etc.

I realize doing a top end is no big deal but I'd rather do this once and have a good running, reliable bike. Who knows, someday maybe I'll ride it 2500 miles to Athena...

One other thing that I'm curious about is cyl head compatibility. I've read about the high dome and low dome pistons and heads on the FAQ's on the SH site and I'm confused. My spare head is #922501 so from a 92C Dirt Squirt. Is that going to work with either the piston I have or whatever I purchase to replace it?

thanks again, you guys are a great help!

Relic

[Charlie R]

Ken, If you use the head from the DS (which is also the stock Ace 100 head) you will need the "high dome" piston. The DS head has a a deep combustion chamber design and if used with the "low dome" 93 piston it will have very poor compression. On the other hand, if you use the Model 93 SR head (which has a more shallow combustion chamber design) you must use the "low dome" piston to keep a reasonable compression ratio.

In short, whatever head you choose, be sure and use the proper piston with the proper crown height.

I hope this explanation makes sense & helps clear things up!

Also remember that when approaching overbores greater than 1 mm (.040), it MAY be neccesary to have the head machined to allow proper piston clearance at TDC. Same thing applies to head gaskets also. I hope I haven't muddied the waters here!

Charlie R

[Zyx]

The photo of Relics piston appears to show a basic four corner seizure, which I would attribute to someone in the past having pushed too hard without warming the bike fully. This is a common problem with nearly all motocross riders, in that no one really warms up their machine before running a hot moto. Also a common issue with almost any piston, but perhaps the design of the Wiseco at that time was more prone than others. Thinner pistons heat faster, and cool faster. Hodaka is an air cooled bike, not water cooled. There are far too many variables in play to say that the problem with the early pistons was this one thing or something else. They didn't all seize.

As for round -- I just measured a new Super Combat piston, original manufacture, standard bore. The dimensions of the piston are: at the ring and for a quarter inch below - round; at the top of the pin boss -- round; at the bottom of the pin boss -- fatter front to back but not much; at the skirt -- distinctly fatter front to back although hard to say how much because it is not a full skirt piston. Top to bottom, tapered fatter at the bottom.

So clearly, even stock Hodaka pistons are varyingly round depending on where you measure. Not having an old Wiseco in hand I can't say, but I doubt they were perfectly round except at the top half of the piston. The difference between the old Wiseco and a stock piston is the thickness of the skirt. Now why would that make a difference?

Because thicker parts expand more when warm. Okay, so the old Wiseco is going to expand a bit more at the skirt when warm than would, say, a stock piston. But so what? All you need to know is by how much. Since it was a popular notion to set up pistons with clearances of one or two thousandths, setting up a heavier Wiseco piston that way would possibly lead to lack of clearance when warm. Okay, so set it up with four or five thousandths instead of one or two. It will dingle when cold, but be fine when hot. I know for a fact you can set piston clearance way beyond three or four thousandths and still work, as I have a Webco 125 top end on an old 93 rat bottom that is set at 8 thousandths. Yes it dingles, and yes it runs, and has run since 1981.

Not saying wide clearance is correct, just that the answer to the question of clearancing a piston differs with application. Sounds like the early Wiseco pistons needed far more cold clearance than did stock pistons, and I bet that wasn't known at the time. The other downside to the older piston is its weight. It is 33% heavier than stock. Put that into a motocross bike, and it sounds like a bad mix all around. But for a street bike, not so bad. You would have to remember to warm it up before driving off.

[racerclam]

I noticed that the wiseco piston in the picture is a real early one , that is a cast piston. Middle period pistons were forged of low silica content aluminum which made for alot of expansion, problem was that most people were un aware that aditional clearence was necessary for that and bored cylinders as if it were a cast piston with a low expansion creating the seizure problems that plagued many, The late wiseco pistons are a high silica content aluminum which does not require as much clearence as the earlier versions. The are much harder as a result and more resistant to scuffing. But also not a malable. Thes pistons are the same material as SRP auto pistons , they are actually the same company.And are great pistons for everything but extreme Horse power applications such as Nitro cars where a more malable piston is desireable . Sorry I didnt really want to get on to cars but address whys!

Rich

[hodakamax]

Good report Rich, and I must say, the extra weight does make a good paperweight on my desk which is the only purpose that it appears to be good for.

Maxie

PS--Actually after that piston seized, I used it to prototype some of our first reed pistons. It's sat on my desk for over 40 years. What ever that's worth---

[racerclam]

After 40 years gravity should have made that piston shorter and fater now you can re machine it for some other application

Rich

[relic]

Bottom line- if I want to use this reed modified cylinder I will need to find either a Super Rat cylinder head or a .060" oversize high dome piston kit?
Some checking suggests that a piston kit is a lot cheaper than the cylinder head.

But before I do any serious shopping I'll pull the engine from the bike and see what condition it is in. And what components are there. I have no idea as the kick starter only slightly moves the crank at the end of its travel.

My hope had been to build up an engine using only my spare parts but if I can make one good engine out of the two that will be good.
This was supposed to be a winter project but patience is not one of my better qualities, so I may be reporting back sooner than later.


again, I have to say a big thank you to everyone! Your expertise is appreciated.

Relic

[hodakamax]

After 40 years gravity should have made that piston shorter and fater now you can re machine it for some other application

Rich

For the next forty I'm going to lay it on its pin side and see if it will go oval like it should be.

Maxie

[Zyx]

Measure carefully around the skirt. You may find it is oval. You may also find that the reasons that Wiseco pistons had issues are not the reasons you have recalled over the years. I have never seen a round piston for an internal combustion engine. All have been cammed. Some are cast, some pressure cast, some forged. Some have thicker skirts than others.

Whatever. From what I have been able to find in researching Wiseco pistons over the years, being round isn't one of their attributes, but being heavy is, as well as being possibly forged. You can not set up a heavy forged or pressure cast piston the same as a light cast piston, and a tip of the hat to Rich for mentioning this issue with old Wiseco pistons. Something I knew in theory, but not from experience because I have always avoided Wiseco pistons. In addition to setting up the older pistons with more clearance, they also require extended warm up and also extended break in. Likely, most folks didn't do that in years past, just as they don't do it now, and end up having the same issues, as reported in modern motorcycle blogs, snow machine blogs, and so on. Seizures are still a problem associated with rebuilds because set up instructions for aftermarket pistons tend to be generic, whereas most folks set up all pistons the same without regard to brand and metallurgy, or follow generic instructions that may not be best practice.

I suspect our recent discussion regarding a Combat Wombat with a Wiseco may have had similar issues, short break in, short warm up, heavy piston, hot moto. But just because we don't understand what is going wrong isn't a reason to condemn the old piston. Rather, use it with caution and proper set up, or buy stock instead.

[Charlie R]

Ken,

Help me out a bit. I know I commented on one of the cylinders that was an early 2 bolt SR cylinder that had been finger ported for reeds. However, I went back and looked at the photo of the bike and it appears to be a standard Ace 100 cylinder with a reed valve. Which cylinder are you wanting to run?