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

Technical Forums for Two-Stroke Nuts
It is currently Tue Aug 14, 2018 6:14 am

All times are UTC - 4 hours [ DST ]




Post new topic Reply to topic  [ 30 posts ]  Go to page 1, 2  Next
Author Message
 Post subject: Flywheel lightening
PostPosted: Wed May 16, 2018 11:10 pm 
Offline
-----
-----

Joined: Sat Feb 08, 2014 5:39 pm
Posts: 1048
Location: Vancouver Is. Canada
Contacted NK racing (UK) about lightening a flywheel for a new engine rebuild. Learnt I had to ship my original to and frow fm Britain to get it done. Mailing would be killer unfortunately since NK's price was decent. A local machine shop could do the job, The attached photo is fm the NK racing site. Has anyone done this mod and how much was shaved off to get a light yet tolerant/functional flywheel?


Attachments:
RD LIGHT FLYWHEEL.jpg
RD LIGHT FLYWHEEL.jpg [ 45.75 KiB | Viewed 507 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Wed May 16, 2018 11:26 pm 
Offline
-----
-----

Joined: Fri Oct 03, 2003 11:11 pm
Posts: 3419
Location: Southern Ontario, Canada
I've got one around somewhere that I did like that, don't recall the exact dimensions but I turned it down based on recommendations at the time. I was meaning to look for it this week before I put my engine together, I'll measure it when I find it. I ran it for quite a while but had to change it when my stator died and it was not compatible with the replacement I had at the time. It revved quicker, not sure how much that translated into real performance.


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Wed May 16, 2018 11:36 pm 
Offline
-----
-----

Joined: Sat Feb 08, 2014 5:39 pm
Posts: 1048
Location: Vancouver Is. Canada
Appreciate it Ruzty. How long ago did you do the mod? Also undertand there is less stress on the crank to boot.


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Wed May 16, 2018 11:40 pm 
Offline
User avatar

Joined: Sat Oct 10, 2009 4:33 am
Posts: 9601
Location: Sydney
The problem people have with these is that the weights and the rest of the flywheel is heavy, so removing metal can cause them to fail if you do it wrong. defo dont do any on the front near the rivets, that part is pretty thin for the weight of the outer part :/

_________________
My Projects:
Yamaha '85 RZ350 F1 & '83 RZ & RD Athena 421 LC & XT500 Supermoto & Honda MT250... See them all on www.2smoked.com

Like Watches? You will love www.PloProf.com & www.DeskDivers.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Thu May 17, 2018 4:01 pm 
Offline

Joined: Tue Nov 12, 2013 2:34 am
Posts: 1080
This was very common with dirt bikes. Biggest issue is maintaining balance when removing material. Have never heard of a flywheel actually coming apart or failing rather they end up junk when they are badly balanced.


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Thu May 17, 2018 4:57 pm 
Offline

Joined: Mon Sep 27, 2010 7:21 pm
Posts: 482
Location: Wellington New Zealand
The picture is how we did mine back in the day. Dont be greedy and no real need to take off front face.
Didn't bother on my big bore but helped the 350 feel more spritely.

_________________
496 Cheetah. TSS PVs, PWK35s, Ignitech, RGV(ish) chassis


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Thu May 17, 2018 8:49 pm 
Offline
-----
-----

Joined: Fri Oct 03, 2003 11:11 pm
Posts: 3419
Location: Southern Ontario, Canada
LC Cnd wrote:
Appreciate it Ruzty. How long ago did you do the mod? Also undertand there is less stress on the crank to boot.


Okay, I found it. I did this probably 15 years ago and used it for several seasons. I took 4 mm off the OD (a 2mm cut) and radiused it at the center ring where the triggers are. I did a straight cut and did not touch the outer radius or front face. I now have a spare stator/rotor assembly that is the same so once I get my engine assembled and broken in I will try a back to back comparison.
Not seeing how there is less stress on the crank, it is a balanced rotating assembly, all you are doing is reducing the inertia of the whole assembly.


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Thu May 17, 2018 9:09 pm 
Offline
User avatar

Joined: Sat Oct 10, 2009 4:33 am
Posts: 9601
Location: Sydney
evan_calgary wrote:
Biggest issue is maintaining balance when removing material.


The idea is to remove only metal from the area that has no balancing dimples or the trigger (of course), that way it should stay roughly in balance.

I like the idea of it, but have never done it. Id hate to weaken the unit and have it fly apart... would be 'messy' :/

_________________
My Projects:
Yamaha '85 RZ350 F1 & '83 RZ & RD Athena 421 LC & XT500 Supermoto & Honda MT250... See them all on www.2smoked.com

Like Watches? You will love www.PloProf.com & www.DeskDivers.com


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Fri May 18, 2018 1:54 am 
Offline
-----
-----

Joined: Sat Feb 08, 2014 5:39 pm
Posts: 1048
Location: Vancouver Is. Canada
Request, is it possible to see a photo of your flywheel Russ? Curious what your flywheel looks like where the front face meets the outside diameter - is it 90 degrees or tapered like the photo above? Funny you should mention the dimples Jon as the machinist whom I'm using was curious if the removal of material might affect the balance. This vid on lightening a Yamaha blaster flywheel is interesting.
https://www.google.ca/url?sa=t&rct=j&q= ... gIdDKHQnzU
Here is how rotational inertia on a motorcycle flywheel is effected by horsepower and why Russ you noted the difference:
https://www.youtube.com/watch?v=CxuER0qIWJk More of a tech tip matter really.


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Fri May 18, 2018 3:54 am 
Offline

Joined: Mon Mar 03, 2014 8:44 pm
Posts: 2808
Location: Alberta, Canada
From the pic, I would have guessed about 0.020" depth of cut, about 1mm total. The lighter flywheel would create less torque on the crank. The result is a quicker reving engine. Too light is not good. You do need inertia. This is, what I consider, an extreme mod. If you are an awesome rider, which most of us are not, and have a hundred of these to cut and test for best results, go to her. Fun to talk about, more fun if you have experience with them...Russ?! Lol

_________________
Rory


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Fri May 18, 2018 11:58 pm 
Offline
-----
-----

Joined: Fri Oct 03, 2003 11:11 pm
Posts: 3419
Location: Southern Ontario, Canada
Here's a pic from when I did it in '02. Looking at it again I recall I didn't turn it down myself, I gave it to a machinist at work as I didn't have use of a lathe at the time. The 2mm dimension came from someone on the old UK forum that had done a number of these, based on cutting one apart. I don't agree with the statement in the video you linked that the 'corner' going into the radius is a stress riser, that is no different than the end of the taper on the crank. It would matter if it was cut into an inside radius. I probably put 10000km on this one, I don't recall it being excessively vibey, but I'll refresh my memory soon. I was a bit concerned that it should have been rebalanced, and I have a crank taper saved to mount it to for that purpose, but never got around to it.


Attachments:
Flywheel1.JPG
Flywheel1.JPG [ 54.55 KiB | Viewed 386 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Sat May 19, 2018 3:06 am 
Offline

Joined: Mon Mar 03, 2014 8:44 pm
Posts: 2808
Location: Alberta, Canada
Yeah, wow, that one is cut down. That looks like a fun mod. I might have to try that.

As far as balancing goes, drilling small divots where it is heavy, is effective.

_________________
Rory


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Sat May 19, 2018 5:54 am 
Offline
-----
-----

Joined: Fri Oct 03, 2003 11:11 pm
Posts: 3419
Location: Southern Ontario, Canada
The amount I removed works out to around 103g or 3.6 ounces.
I used to have an '82 RX7 and swapped in a lightweight flywheel from Racing Beat, 28 pounds down to 12. I also added a heavy duty clutch. Boy did that change the character of the car, more fun when you were having fun but getting stuck in traffic was brutal. Anyone who drove it stalled it 3 times before getting it to move.


Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Sat May 19, 2018 3:41 pm 
Offline
-----
-----

Joined: Sat Feb 08, 2014 5:39 pm
Posts: 1048
Location: Vancouver Is. Canada
I get that balance is key - can this be acheived in a static balance setup, like balancing a motorcycle wheel, or does the flywheel have to be in constant motion to find where to drill to balancing out? Found this photo'd sample on a Harley form. Then there is the question of how much to drill that's the challange. The video, on shaving a flywheel, stated that is not a issue interestingly.


Attachments:
flywheelstand.jpg
flywheelstand.jpg [ 70.48 KiB | Viewed 347 times ]
Top
 Profile  
Reply with quote  
 Post subject: Re: Flywheel lightening
PostPosted: Sat May 19, 2018 9:19 pm 
Offline

Joined: Sun Jan 29, 2006 2:18 am
Posts: 1095
Location: vancouver
Why dick about shaving the old lump ? Find and buy a light flywheel assly .. for a genuine weight reduction ?
There are a couple of units available. Not free, but then Nothing worthwhile ever is.


Top
 Profile  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 30 posts ]  Go to page 1, 2  Next

All times are UTC - 4 hours [ DST ]


Who is online

Users browsing this forum: No registered users and 2 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group