crankcase mod,good idea or not?

[dave32]

After having a good look at the Kr's crankcase intake and catchement area i can see there is some room for improving things,
Ive noticed that on the right side there is a protrusion where the inner clutch cover bolt sits,this could be ground out (breaking through and requiring filling) along with a shorter bolt (there seems to be enough depth).
One thing im not sure on is the oil way/main bearing feed mod,
ive noticed some fill this area just leaving a small hole at the top,my concern is what,
What does this to do to bearing life?
Is there ANY gain (performance wise) in even doing this?
My reason being is,
Ive never come across a purpose built race bike (h***a RS or Yam TZ) that uses this mod,even the Kitted h***a didnt.
All jap mx's ive seen DONT use this mod.
Comparing say a early 90's KX125 intake its obvious thought has been put into this area (more than a KR) but the oil feed is left.
Im not sure if this has an effect or not but due to the KR engine being angled forward when installed,the standard oil feed catch area does just that,any oil/fel mix in this area get caught and directed to the hole.
If you dont have this your relying on fuel thats in suspension finding the now small oil feed hole as the only means of lubricating the mains.
With the stock setup you also have the benefit of oil thats accumulated in this area (oil thats dropped out of suspension) feeding the bearings.
Personally i woud say that providing this area has any edges radiused then thats all thats needed.
Not knocking anyone that does this as i can see why you may think this mod is beneficial,just that after some thought im not sure it will contribute anything to the flow from crankcase to barrel scavange ports,after all if its not used on an out and out racer (not road based) there must be a good reason.
Another mod that i can think of is ,barrel/gasket/crankcase matching,
My thoughts are,providing the step is in the right direction i.e, stepping down from crankcase to barrel then there is no gain in grinding out the case to match the larger barrel area as there is NO hindrance to flow (which would be the case if the step was UP).
Maybe some of these mods are more based on a "feel good" decison rather than it WILL make a difference?
Oh just read the lates classic mag,stan stephens can gain up to 8hp by modding the KR crankcases
Your thoughts?
Anyone?
Regards
Dave

[Luders]

Firstly, I'm not sure which bit of material you are referring to, but it sounds like a good find to me, so I'm going to take a look as soon as I get home.

Secondly, I also fill this area making sure there is a good wide opening for the oil hole area, but I only do this because others have recommended it, I've never proved if it improves the flow.

Thirdly, barrel/crankcase matching I find is good. The base gasket is about right matched to the crankcase, but when you offer the base gasket up to the barrel, there is a step in the wrong direction for flow.
Taking this material away will clearly imporve flow and performance.

Barrel on the right is unmolested


Fourth point, there's only so much crankcase work which can be done and having seen around a 5hp gain on a dyno run from the testing MJ has done over the years, I find 8hp difficult to believe.

[Luders]

Just had a look at a pair of cases and see what you mean now about the clutch casing bolt.

It's all quite smoothly profiled on the one I have here and not sure how much difference taking it back and filling it would do as it's at the end of the inlet flowbefore it travel up the transfers.

I'm willing to give it a go though.

[mj43]

After having a good look at the Kr's crankcase intake and catchement area i can see there is some room for improving things,
Ive noticed that on the right side there is a protrusion where the inner clutch cover bolt sits,this could be ground out (breaking through and requiring filling) along with a shorter bolt (there seems to be enough depth).
One thing im not sure on is the oil way/main bearing feed mod,
ive noticed some fill this area just leaving a small hole at the top,my concern is what,
What does this to do to bearing life?
Is there ANY gain (performance wise) in even doing this?
My reason being is,
Ive never come across a purpose built race bike (h***a RS or Yam TZ) that uses this mod,even the Kitted h***a didnt.
All jap mx's ive seen DONT use this mod.
Comparing say a early 90's KX125 intake its obvious thought has been put into this area (more than a KR) but the oil feed is left.
Im not sure if this has an effect or not but due to the KR engine being angled forward when installed,the standard oil feed catch area does just that,any oil/fel mix in this area get caught and directed to the hole.
If you dont have this your relying on fuel thats in suspension finding the now small oil feed hole as the only means of lubricating the mains.
With the stock setup you also have the benefit of oil thats accumulated in this area (oil thats dropped out of suspension) feeding the bearings.
Personally i woud say that providing this area has any edges radiused then thats all thats needed.
Not knocking anyone that does this as i can see why you may think this mod is beneficial,just that after some thought im not sure it will contribute anything to the flow from crankcase to barrel scavange ports,after all if its not used on an out and out racer (not road based) there must be a good reason.
Another mod that i can think of is ,barrel/gasket/crankcase matching,
My thoughts are,providing the step is in the right direction i.e, stepping down from crankcase to barrel then there is no gain in grinding out the case to match the larger barrel area as there is NO hindrance to flow (which would be the case if the step was UP).
Maybe some of these mods are more based on a "feel good" decison rather than it WILL make a difference?
Oh just read the lates classic mag,stan stephens can gain up to 8hp by modding the KR crankcases
Your thoughts?
Anyone?
Regards
Dave

I grind that bit out. Some times it breaks through other times it doesn't. If it breaks through just fill it. Standard bolt is okay. Would like to see what a stan engine is like. I know mine are good and reliable. On the subject of oil ways I have never had a main fail. Used to get 5 seasons out of a new crank before changing it. Rebuilt cranks have not proved as reliable though problems have been caused by other failures usually barrels cracking. Biggest problem I have is my motors make too much torque! If I remember I will take some pictures of my cases an barrel base.

[TwoStroke Institute]

The intake charge just follows the outer wall whatever shape that is. What really matters in the inner wall. This is where KHI engineers got this cylinder 99% correct. The large radius at the bottom of the inner wall and the difference in area between inlet and outlet of the duct make intake charge cling to the inner wall NOT the outer wall. By intake clinging to the inner wall it makes intake cling to the piston. Better piston cooling =more HP. I doubt the dyno would see a difference betwwen the two cylinders, even suspect the RH would be better.

[dave32]

Thanks for your views guys
Interesting point from TSI
one other thing i wonder about is,
Is it better to "fill in " the area after the reedblock on the side walls that protrude inwards or,grind them out/round/flow the edges so intake charge is directed more towards the transfers?
ive seen both ways done,but after looking at a KX125 intake that doesnt have these KR specific protrusions it seems that having the intake directed towards the transfers would be better,maybe

[maccas]

I rebuilt a friends 1998 KX 125 engine a few months ago and took a few snaps while I was in there:



As you can see on these cases the ramps try to send the mixture up into the transfer tunnels and away from the rotating crank.

The powervalve system on that barrel was very very clever too. It had 4 exhaust ports. A bridged main point along with 2 auxillary kips ports. The main bridged port had a clever guillotine style power valve that lowered and raised its height as well as traditional KIPS style rotating powervalves that opened and closed the sub exhaust ports. Very clever.

I've got a video of the powervalve mechanism somewhere. I'll try and dig it out.

Dan

[TwoStroke Institute]

What does make some HP is if you replace metal with fuel and air apparently. Another one it look at is the transfer duct being smaller than the exit and last but not least is a very small volume exhaust duct.