Ton up SR250: 100mph, 100kg, 30hp

I found it! I knew I had read somewhere in one of my speed books about the PCV system connected to exhaust rather than intake - see attached. Also, this other extract below is taken, believe it or not, from the Wikipedia page about PCV valves:

'Not all petrol engines have PCV valves. Dragsters sometimes use a scavenger system and venturi tube in the exhaust to draw out combustion gases and maintain a small amount of vacuum in the crankcase to prevent oil leaks on to the race track.'
 

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I had heard of exhaust-induced depressurization before but I don't see the benefit (vs cost/complexity) of using this system over the intake-induced depressurization 1-way valve I mentioned much earlier. Any references speak to both and cite the reasons for the preference?
 
Your crankcase already vents to atmosphere, or in stock form to the air box. Draw through the airbox helps produce vacuum similar to the way a pcv works, which draws from an intake. Using the exhaust is a pretty common, pre-pcv, old school way of doing it on V8s.
 
irk miller said:
Your crankcase already vents to atmosphere, or in stock form to the air box. Draw through the airbox helps produce vacuum similar to the way a pcv works, which draws from an intake. Using the exhaust is a pretty common, pre-pcv, old school way of doing it on V8s.
Right - except that vacuum is only present in the crankcase when the piston is moving upward; otherwise it is a series of push-pull movements which is the windage loss described. My previous suggestion was to use a 1-way Krankvent (used by the H-D crowd for the same reason) in the OEM line going from crankcase to intake so as to create a vacuum in the crankcase. I didn't know if Jadus' research had uncovered if the exhaust-induced vacuum method was better or...
 
zap2504 said:
Right - except that vacuum is only present in the crankcase when the piston is moving upward; otherwise it is a series of push-pull movements which is the windage loss described. My previous suggestion was to use a 1-way Krankvent (used by the H-D crowd for the same reason) in the OEM line going from crankcase to intake so as to create a vacuum in the crankcase. I didn't know if Jadus' research had uncovered if the exhaust-induced vacuum method was better or...
Smart. I hadn't though of running a Krank Vent on a jap bike.
 
Good points. I haven't drawn any conclusions, only that the stock system (and many other jap bike systems for that matter) are sub optimal because they draw up a certain amount of oil mist from the crank cases into the engine - affecting combustion and having many negative affects on power and engine wear. Tapping into the exhaust just sounded like a good way to avoid this entirely. But with the addition of a valve, I struggle to see the benefits over the intake pick up? Why would dragsters and many race cars hook into the exhaust instead?

irk miller said:
Using the exhaust is a pretty common, pre-pcv, old school way of doing it on V8s.

I like! Seems simple and obviously worked decent enough for years until better systems were made.

Think I'll still use a valve though, otherwise there'll be a bunch of burnt oil mist in the exhaust...
 
Yesterday evening was pretty exciting for me! Received the first prototypes of the adjustable fork caps I have designed. They look and feel top notch! They installed flawlessly as well. Just a couple of adjustments to make the covering cap (completely cosmetic and non-functioning) stay in place better (it works its way upwards over time).

I took a couple of shots of how the assembly looks and what it is like to install it as well. A damn site easier than the stupid system from the factory. Did they do it like this to make it difficult for customers/owners to mess with the forks themselves? So it required special tools/knowledge to get into them?

I ordered 3 sets, one goes on the daily rider for immediate testing, one set is for this project and the last set is for a test house or a competent workshop with a large press and digital load read out that can log data. They will be both load/stress (max until deformation detected) tested and spike tested (hit suddenly with a certain force) several times. I also have a colleague who is very capable with FEA software who is running some simulations for me. Basically, I am extremely paranoid about the safety of these - very little for my own safety (because I personally trust the engineering) but a boat load for the market/potential customers/users. So to have some safety data on them is critical!
 

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Now I am measuring up everything to draw up some custom swingarm bushes. I looked into roller cage bearings as well and correct sizes are available but from what I've read, they do not bring any benefits to the table. Or is there something I am missing?

If I draw up the bushings, I should then also draw up some custom inserts as well right? In stainless steel so they don't corrode?

I am also looking into what I can do about the seals - something better than the stock ones that obviously allow crap to come in.

Just look at the wear from the stock bushings :eek:
 

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A bronze bushing has a much higher load rating, but they have a tendency to oval and develop slop over time. This is why most dirt bikes have gone to needle bearings. The load rating on a good SKF type needle bearing, though, is going to be way more than what will ever be experienced on most any motorcycle. So essentially, a good needle bearing will be practically maintenance free for a really long time. They can be bought with a port drilled in the jacket to be lined up with a zerk fitting for the occasional greasing.
 
Thanks for the input. Perhaps I should revisit this. It is after all easier and should be cheaper (standard items vs custom machined). The machined parts would cost a lot as well based on the necessary tight tolerances.

I noticed when looking for bearings that there is often seals that go with them/seals that suit the bores the bearings are designed for. Then I just need to have some spacers machined up to control the placement depths of the bearings each side of insertion, plus some spacers to take up the missing space of the weird stock seals (if I find other ones that I think are better). The stock ones are some kind of cap seal solution which seams unnecessary if a good internal seal is installed.
 
Just food for thought, but I always wanted to use some preloaded angular contact bearings, similar to what is used in automobile uprights. They are sealed and can handle side loads as well as vertical. Would be perfect for a swingarm, the only down side might be their size. Needle bearings are such a bastard to keep clean and smooth functioning, at least they have been all of my MX bikes. It's probably less of an issue on a road going bike.
 
irk miller said:
A bronze bushing has a much higher load rating, but they have a tendency to oval and develop slop over time. This is why most dirt bikes have gone to needle bearings. The load rating on a good SKF type needle bearing, though, is going to be way more than what will ever be experienced on most any motorcycle. So essentially, a good needle bearing will be practically maintenance free for a really long time. They can be bought with a port drilled in the jacket to be lined up with a zerk fitting for the occasional greasing.
I know that the XS650 originally came with plastic bushings in the swingarm and Mike's XS has sold quite a few bronze replacement kits.
 
Same with the RD's, plastic bushings OEM.

I have a set of Mike's bronze bushings and they work a treat, the price is good too.
 
Received these brackets the other day after getting back from holiday. Now onto making the linkages!
 

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