RZ/RD 350 & Misc. 2-Stroke Tech BBS

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PostPosted: Thu Oct 11, 2018 12:03 am 
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Posts: 37
Location: Bay Area CA
WOW Thank you guys so for the detailed input.

Out of paranoia before dumping more time into it - I checked the crank tolerances tonight. According to my service manual, crank-side bearing play is spec'd at .010-.030" and mine fell at .022" and .023". Small end 'wiggle' is spec'd at .014-.039" and mine fell at .048" and .052"! It doesn't *feel* like too much wiggle, but apparently this is too much! Is that an assembly tolerance that is normal to open up, or is this thing trashed?

Is this the kit you're referring to, or should I just buy a crank and then get OEM seals separately?
http://www.hotrodsproducts.com/ProductI ... em_id=5655

Suddenly, it starts adding up...
$500 bottom end kit
$250 bore&hone both cylinders
$200 piston kits
$100 misc top end gaskets

:smt030


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PostPosted: Thu Oct 11, 2018 1:43 am 
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Video of engine:
https://youtu.be/4vQ7prsUAtI

I feel zero perceptible radial play on both. Zero on the piston side either.


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PostPosted: Thu Oct 11, 2018 2:57 pm 
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Yes that's the kit. Do that or the OEM Yamaha Banshee crank. Either will last you the life if your bike.

Do you have pipes?

Also I forgot to mention, add a set of reeds, TDR fiberglass reeds work pretty good. A low buck part that really helps.

You should rebuild the bottom end to be safe and secure.

You don't need anything wild or too expensive to make the RZ a quick lil toy.

Stay away from unnessesary upgrades like Aftermarket heads,O ringed stock heads, larger Mikuni or PWK, cylinder port work etc.. While they all work, you DONT need any if it.

(Pipes are mandatory though)....gotta have them. You'll gain anywhere from 5-13 h.p. just from pipes and your RZ should be about a mid 50 h.p. toy

Just go OEM as much as possible, add pipes, reeds, gearing and the head milling.. & your good to go.
At 1000 miles a year ...it will never fail you, no matter how hard you pound on it, as long as it's built to specs with req parts😉

TDR is Tony Doukas Racing, he's a member here and can provide all your parts plus milling your head, I think you can get a forum member discount too.
You might also try any of the following, all are trusted and reliable friends of the RZ community.
Fast from the Past.
Economy Cycle.
Wicked ATV.
Spec 2.

With the above mods, you going to have a bike that's a smile a minute, lil wheelie Machine. You'll always be happy to go out and ride...it's just the nature of the bike. Small light and fun fun fun. They haven't made anything much like it since.

_________________
Banshee (Baja) race bike, Lonestar A-Arms, dual 9" L.E.Ds, FMF, Toomey,19cc domes, IMS tank, run flats.
96 GSXR SRAD, Future Yoshimura Lucky Strike rep.
85 custom Tri-Z
RZ/YZR track bike(project)
86 VFR750 RC24 Merkel replica (project)


Last edited by Questo vecchio rz on Thu Oct 11, 2018 3:14 pm, edited 1 time in total.

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PostPosted: Thu Oct 11, 2018 3:13 pm 
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Location: New Hampshire USA
kobra wrote:
Video of engine:
https://youtu.be/4vQ7prsUAtI

I feel zero perceptible radial play on both. Zero on the piston side either.


Watching your video, it looks like there has been some contamination dirt/humidity/blow-by especially on the right side. I have a lot of dirt-bike experience and can say that when you do a budget rebuild of an engine that looks like that and skip the bottom end, it will cost you more the second time around! If the engine internals were exposed to humidity for extended time, it's pretty likely the bottom rod bearing will disintegrate in less than a season of riding. Plus if those little specs I see in your video are dirt, you'll never be sure that you got it all out by rinsing air-blasting etc.

_________________
A modest "high" can be obtained by listening carefully to the sound of a 2-stroke hitting the fat part of the powerband while inhaling cool fall air tainted by the exhaust scent of VP-C12 and Golden Spectro, mixed at 24:1.


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PostPosted: Thu Oct 11, 2018 3:48 pm 
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Joined: Sun Sep 16, 2018 12:53 am
Posts: 37
Location: Bay Area CA
Questo vecchio rz wrote:
Yes that's the kit. Do that or the OEM Yamaha Banshee crank. Either will last you the life if your bike.

Do you have pipes?

Also I forgot to mention, add a set of reeds, TDR fiberglass reeds work pretty good. A low buck part that really helps.

You should rebuild the bottom end to be safe and secure.

You don't need anything wild or too expensive to make the RZ a quick lil toy.

Stay away from unnessesary upgrades like Aftermarket heads,O ringed stock heads, larger Mikuni or PWK, cylinder port work etc.. While they all work, you DONT need any if it.

(Pipes are mandatory though)....gotta have them. You'll gain anywhere from 5-13 h.p. just from pipes and your RZ should be about a mid 50 h.p. toy

Just go OEM as much as possible, add pipes, reeds, gearing and the head milling.. & your good to go.
At 1000 miles a year ...it will never fail you, no matter how hard you pound on it, as long as it's built to specs with req parts😉

TDR is Tony Doukas Racing, he's a member here and can provide all your parts plus milling your head, I think you can get a forum member discount too.
You might also try any of the following, all are trusted and reliable friends of the RZ community.
Fast from the Past.
Economy Cycle.
Wicked ATV.
Spec 2.

With the above mods, you going to have a bike that's a smile a minute, lil wheelie Machine. You'll always be happy to go out and ride...it's just the nature of the bike. Small light and fun fun fun. They haven't made anything much like it since.


I have stock pipes that are rusted out - so I will need new ones.

Thanks for your input. I need to think this all over. See below

brrrappp wrote:
kobra wrote:
Video of engine:
https://youtu.be/4vQ7prsUAtI

I feel zero perceptible radial play on both. Zero on the piston side either.


Watching your video, it looks like there has been some contamination dirt/humidity/blow-by especially on the right side. I have a lot of dirt-bike experience and can say that when you do a budget rebuild of an engine that looks like that and skip the bottom end, it will cost you more the second time around! If the engine internals were exposed to humidity for extended time, it's pretty likely the bottom rod bearing will disintegrate in less than a season of riding. Plus if those little specs I see in your video are dirt, you'll never be sure that you got it all out by rinsing air-blasting etc.


I am pretty sure the right side is the one that melted the piston. Then this engine has sat open for the last 15 years with nothing but a t-shirt covering the hole. Assuming the crank was physically okay, my plan was to remove it and thoroughly flush it of any debris. I was happy to find that the bearings are thoroughly bathed in oil with no corrosion, and it spins freely and smoothly.


Okay here's the million dollar question. Let's say I cheap out and run it with the bare minimum to get it running. In X amount of miles, the crank has worn and is starting to make noise. What are the consequences? Is it just a simple crank swap and labor to replace it, or am I liable to destroy something else? I am not entirely familiar with 2-stroke failure modes. It's clear that when people melt a top end they can just replace the top end - so does a bottom end failure also destroy the top end or is it isolated?

If you can't tell I'm still on the fence about cheaping out vs a full rebuild. It hurts me a little bit to put $900+ into the engine alone when it still won't be pristine (cause of the cracked case near the cs sprocket).


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PostPosted: Thu Oct 11, 2018 10:45 pm 
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Location: New Hampshire USA
How long will it last?
Well it's hard to know for sure. It is entirely possible the thing never blows up. But what I've seen and personally had happen is this:
The rod bearing disintegrates, spewing very hard metal bearing bits that get sucked into the cylinder and into the main bearings. With bore-able iron liner cylinders, it might only need a new crank, top-end, cylinder bore and some resurfacing of the combustion chamber. Gaskets, seals, your time etc.
You will feel it as a vibration and loss of power. I've had this happen on a YZ490. I actually drove the YZ490 about six miles home on trails with a trashed lower rod bearing! Of course, with a single cylinder, rebuilding a crank and top end is simple and relatively cheap. I think that little escapade cost me about $400 back in 1982. My friends CR125 lower rod bearing went and the rod broke at the crank-pin. The down-force momentum from the piston and broken rod punched right trough the bottom of the cases. He was done for the year.

Now, here's real expensive scenario: Let's say you're hammering the bike, showing your buddy what a two-stroke 350 can do, the rod bearing disintegrates, the rod itself breaks above the pin and the good side of your twin cylinder continues to run. Half of the broken rod, still connected to the crank and spinning at high RPM, driven like a circular saw by the good cylinder, literally cuts the cases in half! It takes less than 5 seconds. This I saw on a Yamaha Phazer snowmobile 488cc twin. Total loss. It damaged the cylinder, destroyed the upper and lower cases and obviously the crank was junk. There was chunks of metal everywhere! I wish now that I had pictures!
If the con-rod breaks around the bearing area in a twin and the engine is at high RPM, the crank pin will cycle around and punch something through the cases every time. Even at low rpm, if you are riding, the momentum of the engine being driven by the rolling wheels through the transmission will spin the crank until something breaks or you pull the clutch. Usually by the time you know it it is too late.

The bad news gets even worse for us street motorcycle riders as we are on two wheels and often in traffic or have a passenger. Imagine your bike seizing up or throwing a rod during a wheelie, a turn, or in traffic on the hi-way. There is way too much at stake to half-ass an engine rebuild..... In my opinion.

_________________
A modest "high" can be obtained by listening carefully to the sound of a 2-stroke hitting the fat part of the powerband while inhaling cool fall air tainted by the exhaust scent of VP-C12 and Golden Spectro, mixed at 24:1.


Last edited by brrrappp on Thu Oct 11, 2018 11:48 pm, edited 1 time in total.

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PostPosted: Thu Oct 11, 2018 11:40 pm 
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Location: Bay Area CA
brrrappp wrote:
How long will it last?
Well it's hard to know for sure. It is entirely possible the thing never blows up. But what I've seen and personally had happen is this:
The rod bearing disintegrates, spewing very hard metal bearing bits that get sucked into the cylinder and into the main bearings. With bore-able iron liner cylinders, it might only need a new crank, top-end, cylinder bore and some resurfacing of the combustion chamber. Gaskets, seals, your time etc.
You will feel it as a vibration and loss of power. I've had this happen on a YZ490. I actually drove the YZ490 about six miles home on trails with a trashed lower rod bearing! Of course, with a single cylinder, rebuilding a crank and top end is simple and relatively cheap. I think that little escapade cost me about $400 back in 1982. My friends CR125 lower rod bearing went and the rod broke at the crank-pin. The down-force momentum from the piston and broken rod punched right trough the bottom of the cases. He was done for the year.

Now, here's real expensive scenario: Let's say you're hammering the bike, showing your buddy what a two-stroke 350 can do, the rod bearing disintegrates, the rod itself breaks above the pin and the good side of your twin cylinder continues to run. Half of the broken rod, still connected to the crank and spinning at high RPM, driven like a circular saw by the good cylinder, literally cuts the cases in half! It takes less than 5 seconds. This I saw on a Yamaha Phazer snowmobile 488cc twin. Total loss. It damaged the cylinder, destroyed the upper and lower cases and obviously the crank was junk. There was chunks of metal everywhere! I wish now that I had pictures!

The bad news gets even worse for us street motorcycle riders as we are on two wheels and often in traffic or have a passenger. Imagine your bike seizing up or throwing a rod during a wheelie, a turn, or in traffic on the hi-way. There is way too much at stake to half-ass an engine rebuild..... In my opinion.


Yikes!!!! And I thought my Kawasaki Concours 1000 gave me nightmares... (hydrolock)


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PostPosted: Mon Oct 15, 2018 11:52 pm 
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Location: Bay Area CA
I've been reading up on setting the squish. From what I've learned, too little squish (stock) can't hurt, it just isn't optimal for power. Too much squish can lead to detonation. I had no idea it played such a big role in fuel mixing, the more you know!

I have read about some people simply peeling a layer or two off the stock multi-layer head gasket to achieve the correct squish values. Is that... normal, or frowned upon?

Regarding my rebuild - I am going to bring my engine to a reputable engine repair shop nearby who will be boring/honing the cylinders, to get a professional input on it. There are some things that are just based on feel and I quite grasp through the internet! Regarding the connecting rod wiggle, it is actually still within spec. Upon further research, the install spec is .014-.039" with a service limit of .080" (this value was not in my service manual, but instead in the Banshee manual).


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PostPosted: Tue Oct 16, 2018 3:27 pm 
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kobra wrote:
I've been reading up on setting the squish. From what I've learned, too little squish (stock) can't hurt, it just isn't optimal for power. Too much squish can lead to detonation. I had no idea it played such a big role in fuel mixing, the more you know!


squish has 2 main properties : the gap and the area.
a stock engine certainly does not have a too little squish gap, so I suppose you are talking about the area ? but area alone means little without the gap. too big gap can lead to deto.

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PostPosted: Fri Oct 19, 2018 11:19 pm 
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Location: Bay Area CA
Just wanted to share some info. I dropped off the cylinders to get reworked today. The shop is run by a seasoned engine builder who used to work at a Yamaha race shop and worked on RZ's and TZ's back in the day.

He checked my crank and noted it looked quite good. Everything is still tight and smooth. He recommended opening the webs to the maximum tolerance to help with oiling, and welding the crank if the bike will be hopped up or tracked. Since I plan to keep it stock and it hadn't walked at all I decided to leave it as-is.

We were trying to figure out why the piston fragmented in the first place. There is evidence that it was run for a little while before it finally stopped, as there is excessive black soot around the side of the piston. It's possible that the exhaust pipe was clogged or plugged up - which is plausible since this CA version has 3 catalytic converters. Or possibly it sucked transmission oil into the combustion area. He recommended running premix the first tank to be absolutely sure the oil delivery system is working, then switching over.

I decided to go with Wiseco's using the next available size up (still at stock 64mm bore, so whatever it takes to clean up the damaged side). It will take a bit of removal to clean up the one cylinder since it has some notable grooves. I've read a lot of mixed results on the Wiseco's online and researched it thoroughly. Theoretically a forged piston will be better in every way - stronger, tougher, lighter. According to my research if you bore the cylinder to the correct piston clearance spec it will work fine - it's when people put new pistons in an old worn out bore that they can have issues - either excessive play, or too tight tolerance.

I do tend to ride my bikes hard, so I am wary of doing any upgrades that will sacrifice longevity. I would rather have a slightly slower build that I can ride normally than a more powerful build that is more delicate, if that makes any sense!

Anyway, just thought I'd share that info! I could tell this guy was a wizard when it comes to these bikes. He accurately guessed the axial rod play within .001" just by feel. So I am comfortable with him doing the work.


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