Whats All This Fuss About Crankshaft Smoking?

[70 marlin]

Professor Gorr, thank you for your insight.

 

[RJH]

Thanks Eric - the spacer answer - that makes sense, that's one less thing I have to think about ;) - I guess many of the RS parts fit the CR but the TZ parts don't fit the YZ. On another post you thought the TZ reeds may be stiffer - I'm sure your right, I saw some pictures from the 90's and it seems they had a smaller reed fiber on top of the standard reed to make it stiffer at least on late 90's bikes. A company is sending me some stiffer reeds to try.
Thanks Bob Hogg

 

[demographic]

Originally posted by cr-man
titanium connecting rod did they ever go into production? Is titanium a good rod material?

I am sure that Yamaha made its 4 cylinder 0W01 (I think it was called the FZR 750RRSP or something like that)homologated road racebike with Titanium conrods about 8-10 years ago. That was reliable as far as I heard and if you go onto the PHOTON APTEC website there is info that suggests that coated piston rings last far better in coated bores (Apticote 2000), also there are a few articles by some bloke that I can't remember the name of :D

 

[whyzee]

Eric,
Great information, just a fantastic read.
Have enjoyed your book and more important, have enjoyed your work! The YZ133 is awesome, after jetting the thing and re-gearing, it is a little rocket!
Now if you ever want to play with my twin cam 88B fuel injected ride, just let me know. Looking for about 125 bhp, I feel comfortable it will be in good hands.
Thanks again,

 

[RJH]

Dave - great pics -I see you are using the old TMX carb - I will be selling my spare 2001 TMXx OEM Yamaha carb on ebay soon - 38 mm . The teams say it is much better than the TMX carb. Jet needle (spray tube) is all brass including the extension in the throat of the carb - not cast aluminum. Just a nicer built carb. The slide is metal to prevent wear and give a better seal. It uses a standard hex main and standard long pilot with a brass inlet needle seat. The float level is higher as well. The mid range is lean with about a 440 main. Bob Hogg

 

[SFO]

Originally posted by 96whyzee125
Eric,
Now if you ever want to play with my twin cam 88B fuel injected ride, just let me know. Looking for about 125 bhp, I feel comfortable it will be in good hands.
Thanks again,

I have a friend who just finished a 110" twin cam that makes over 100ft pounds of torque from 3thousand rpm.
It is all stock appearing.
If you can't wait for the magazine article pm me and I will give you his #.

 

[whyzee]

thanks Bob,
rebuilding the YZ was a blast, let me have first chance on the bubble back tmxx bidding when your ready!

& thanks Bill
To be honest, she is only a year old, with less than 5k. I have done all the chrome and performance mods, but I don't trust myself to pull the 88 out to replace the jugs, cams, head work, and everything else needed to make it the beast it could be. I think, maybe, I should have bought the "big dog" pit bull w/ the 250 rear and gone from there, ... I'm sure $$'s wise I'd be ahead in the long run.

 

[Offroadr]

Originally posted by 96whyzee125
I think, maybe, I should have bought the "big dog" pit bull w/ the 250 rear and gone from there, ... I'm sure $$'s wise I'd be ahead in the long run.

Except when you decide to sell it!! The Big Dogs, Titans,BBWs, AMCs and others don't have the resale that HDs do.

Back to the originally scheduled topic. Great reading Eric!

 

[KawieKX125]

Eric, while we are on the topic of crankshafts and related components, are the gains from polishing the die marks off of a foged rod appreceable, and to what degree? Also, it seems like a bunch of snake oil to go welding the pin into a 1 cylinder crank as there is really no way possible for it to spin IMO. Is this correct or does it really help some?

 

[EricGorr]

Kawie KX125
Most rods are case hardened and shouldn't be polished. Theres so much turbulence in a two-stroke crankcase that polishing won't make any difference. However in four-stroke engines the problem of windage (oil bonding to the crankshaft and rod) can be reduced by polishing and coating certain parts. Teflon is often used to prevent oil from sticking to crankcase walls and crank weights.
Regarding the pin welding, sometimes when a crank is rebuilt too many times, the fit and finish of the pin and pin holes wears making it easy for the crank halves to pivot on the pin and throw the crank out of true. Even as little as .005 inch can be noticed in handlebar vibration.

 

[motometal]

regarding the rod polishing-I believe that part of the reasoning behind rod polishing (in general) is to remove stress risers, that is, remove all of the imperfections in the surface of the part. A component will fail in an area with a notch, sharp edge, pit, drilled hole, etc. Polishing a rod for this purpose is only useful if the rod is possibly going to be near the point of failure from fatigue, tensile forces, etc.

I wouldn't want to say that rods NEVER fail in dirt bikes, but it's pretty rare if they ever do.

 

[cr-man]

Hey Eric have you had a chance to test Larry Witmer's bike yet? If so what did you think?

 

[EricGorr]

I haven't yet recieved the crank from Crank Works, but we'll be testing it after Lorettat Lynn's. Larry is riding his ported stock displacement CR against all the guys with big 4 pokes. I put my money on Larry for the +45yr. championship!

 

[MikeS]

Hey Eric

Great info. One thing though with all the techno nuts out there amd big bucks getting shelled out, I am suprised that no real balancing data or techniques exist for the masses. I am good with automotive stuff and have learned to run a few machines that balance those cranks.

Do 4 stroke singles need to be treated differently ? I am suprised to hear that balancing for 6000+ rpm can possibly create vibration at 2500-4000. I wonder if actual flywheel/ignition,bearings and gear is all being done?

 

[bclapham]

OK, i am bumping this one as well.

lets take the case of a 4mm stroker, the pin is moved further out by 2mms.

if we use the same rod, then we have to decide what happens with the extra travel, you can either take material from the head, or shim the cylinder up 2mm with a base place.

assuming the cylinder was setup before to produce peak at 11K RPM, how would we alter the cylinder to keep the powerband the same, ie not turn the engine into a stump puller or top end screamer? eg how do we shim the cylinder and what ports do we alter?

also, i am slowly getting around to reading the Bell book. It says that if the piston goes below the exhaust port at BDC then this seriously effects the gas flow out of the cylinder.....i am sure this would be a problem with the stroker at BTC???????

 

[Ol'89r]

Norm, I've heard about the shrinking rod concept but don't quite understand it.QUOTE]


Eric/Norm.

Excellent article Eric. Always enjoy reading your stuff. :thumb:

In regard to the rod shrinking, the way we did it when I worked for Long Beach Honda Racing was to heat the rod with a torch and crush it in a press. :ohmy: Well, a little more to it than that, but that's the basic proceedure.

We had a fixture that we put the rod in that kept the rod straight and gave you a stopping point inorder to keep the length correct. We machined the crank with a new pin hole and had Venolia make us a piston to the proper specs. That is also the way Powerall does it. Not sure who they use for their pistons though.

As crude as it sounds, we never lost a rod.

Gilda, what a sweetheart. :worship:

Ol'89r

 

[cujet]

At work, I do some helicopter main rotor and tail rotor balancing.

I have used my ACES equipment to learn about and modify the balance factor on a couple of motorcycle engines. In particular, I spent a bunch of time understanding crankshaft balance on my '94 Husky 360 2 stroke. What I determined (with velometers installed in both X and Y axis) is that changing the balance factor increases vibs in one axis and reduces the other. That makes sense if thought about for a bit. I tried various RPM's and found that there was an optimum point for my engine. Any deviation from the optimum point (about a 53% balance factor) resulted in higher vibes in one plane or the other. Vibes in the Y axis seem to be more annoying on my bike.

No matter what weight I added, I could never make the engine smooth at a given RPM, which of course, I knew already.

I was able to add weight externally to the engine, AND there was some improvement to be had. Still, my bike has plenty of vibration at higher RPM's

Chris

 

[DEANSFASTWAY]

Bclapham : How about if a the piston is at TDC and the exhaust port floor is open a bit under the Exhaust skirt on the piston. I know a guy that stroked a big bore RS 125 and had that trouble because the cyl was overported by his knucklehead buddy with a dremel,the thing runs real fine up top though .I was thinking of reversion or dilution of crankase mix at low speeds possibly but with The Revs up I guess Extraction would keep things negligible or woukld it cause a slight draft under the piston. Its a microsprint on alky 58mm bore . Hes actually not doing any better than with the CR motors that he had running 58mm piston. I would think you wouldnt want any area under the exh skirt , why would anyone hog out the bottom of the exhaust port floor so low anyway , wasting $$$.This was a fresh 58mm RS cyl .

 

[bclapham]

dean- i now see why that would be a problem. right now, the bike is running really good just with the 58mm kit- its fast and i dont know that i want to change the personality of the engine and i dont know that i want all the trouble playing with gaskets and carbs to get it running right.

i think i will just leave it as is, and when its time for the crank, maybe go with the longer rod from the 04 with a spacer plate, just to help up top a tad more.

thanks