Anyone else tried this ?

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rovanmadlunatic

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http://www.kingmotorrc.com/engine/hp-gas-engine-30.5cc-4-bolt-big-bore-rebuild-kit/

I bought one because it looked like a good deal. I was pleasantly surprised by the quality. I would say its better than the cy i,m putting together. It comes pre modded, with eybrow ports cut, larger intake and exhaust and the piston has the anti seize relief machined as well as the skirt on the intake side shortened. I haven't assembled it yet but it def looks promising for the price.
 
These come stock on the new models of KM X2 ... The 30.5cc Fuelie new revby king motor.

There okay but somewhat week I shot small hairline crack on fly wheel case and the bottom end after one small crash!
 
X2Boss said:
These come stock on the new models of KM X2 ... The 30.5cc Fuelie new revby king motor.

There okay but somewhat week I shot small hairline crack on fly wheel case and the bottom end after one small crash!
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Wow i thought the castings looked pretty decent. No way to know for sure though until it,s been put through the paces. I love to mess with two strokes so I,m always looking for budget priced specimens.

How is it power wise? The eybrow ports need touching up to optimize them and I haven't had a chance to check the timings but with the bigger Int/Ex ports it should be pretty decent.
 
Ya in the picture it looks worse than it really is. The machining marks are slightly rougher than my cy cylinder. Hopefully it will help hold oil on the cylinder walls. The actual plating on my cylinder looks quite good. I am curious to see how it stands up. I did a quick check on the timings. It def seems to be aimed at low end power which makes sense if its used in the x2. It will be interesting to see what I can squeeze out of it.
 
I sure would not use a picture like that to sell something! Been a motor machinist for 40 plus years and on a nickel seal cylinder any roughness is not good on the plating. It is not like a cast iron or cast iron sleeved cylinder where you want a cross hatch. The reason for nickle cylinder is to make it smooth and have less friction.

I have talked to people that sell KM motor parts and from what they told me I rather stay with what I have found works with out a problem Zenoah and
CY.

But interested to see what the end user has to say.
 
The picture does look bad I will agree. When I bought it i didnt expect it to last as long as a zen, but i am experimenting with some porting mods and don't want to cut into a higher quality motor until im satisfied with what i,m doing.in the end if the plating doesn't hold up i,ve still got the other parts to make use of.
 
20150526_144151.webp

While getting set to start modding this motor I discovered something very odd(and not at all good). When the motor is assembled with the supplied parts, the exhaust free ports by close to 1mm. Any attempt to rectify by stacking gaskets would increase the squish/cr to much larger than desired. Im not sure how they missed this or if all the 30.5 motors are like this but it is not good. Anyone running this motor might want to check to see if they have the same problem. A taller piston would fix it but so far I am unable to find any that are tall enough.
 
I was able to find a piston that should work. It will require shortening of the skirt to clear crank and a bit off the top to set squish. I don't mind the challenge so i chose it over sending it back and paying for shipping etc. I will continue posting once i have it and progress through the build. If it works this should be a killer engine.The huge intake port make it a perfect candidate for a reed block I have been working on. The new piston looks to be more robust than the stock ones so the extra windows i will need to cut will reduce some of the weight.The only question will be the longevity of the cylinder plating.:rolleyes:
 
I have sent off the picture to Dan from KM,s.He is going to forward it to manufacturing to have them look into it. I will be interested to see what comes of it.Obviously the trucks that come with this motor are running but if they have this issue they will most cert be loosing power and possibly wasting fuel.
 
Well I received the piston I ordered to use with this cylinder. It seems the info on the sellers website is wrong. The piston was a perfect fit and would have solved the free port issue but it had the wrong size wrist pin.So im kinda ticked because i waited two weeks for it and cant use it. I will likely have to pay for return shipping and I still Cant use the motor kit.
 
This gets better and better. After a couple emails to Dan he is making no offers to rectify this . He also tells me that most of the KM,s have this issue. Not ideal but they still run. Hmm so basically he is selling motors that have a known issue with no attempt to rectify it. If thats the way they do business it will def be the last dollar they get from my pocket.
 
Boy I just love dealing with companies who don't keep their word or stand behind what they sell. I bought the piston kit from pocketbikeparts.com. Before I ordered it I checked at least half a dozen times to be sure it used a 8mm pin. And thats what they showed on their site. I even checked again after I got it too make extra sure it wasnt my mistake. Nope 8mm just like I thought. Now they have ignored multiple requests to return it based on the incorrect info on their site. I decided to check this am and they have now changed the info to read 9mm pin so they obviously read my request and are just choosing to ignore it.
 
rovanmadlunatic said:
Boy I just love dealing with companies who don't keep their word or stand behind what they sell. I bought the piston kit from pocketbikeparts.com. Before I ordered it I checked at least half a dozen times to be sure it used a 8mm pin. And thats what they showed on their site. I even checked again after I got it too make extra sure it wasnt my mistake. Nope 8mm just like I thought. Now they have ignored multiple requests to return it based on the incorrect info on their site. I decided to check this am and they have now changed the info to read 9mm pin so they obviously read my request and are just choosing to ignore it.
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i bought a zenoah piston for my km 30.5 it is taller after lapping the top of the cylinder with the stock gasket im at .014 squish. i had to surface grind the washers to get them to fit think i had to take about .004 off the washers to make them fit nicely. im also running a reed block so i added windows and lightened the piston a bit.

the plating on the cylinders suck but that didnt stop me from trying to make some extra pony. im on my third motor build with the km 30.5 now.
 
46u said:
I sure would not use a picture like that to sell something! Been a motor machinist for 40 plus years and on a nickel seal cylinder any roughness is not good on the plating. It is not like a cast iron or cast iron sleeved cylinder where you want a cross hatch. The reason for nickle cylinder is to make it smooth and have less friction.

I have talked to people that sell KM motor parts and from what they told me I rather stay with what I have found works with out a problem Zenoah and
CY.

But interested to see what the end user has to say.
Click to expand...

This all sounds like a disaster ...

I'm with you 46U - I think we should stick with what works & is proven.
Not to mention simple to build ... ;)
 
Well i certainly would not have bought it if i,d known about the free porting problem. But since Dan was not going to make it right i was stuck with it.And then because I was also stuck with the piston because another dead beat retailer would not make good on their screw up the $ were starting to add up. I don't expect it to last a long time. If i even get the summer out of it thats fine, and Im not one to take the easy way...:lol: For me half the fun of owning a baja is it gives me an excuse to play with motors. I have sort of a thing for anything 2 stroke.Maybe because it reminds me of myself:w00t: I already have two more motors to use if this one blows.
 
Throttle Switch said:
i bought a zenoah piston for my km 30.5 it is taller after lapping the top of the cylinder with the stock gasket im at .014 squish. i had to surface grind the washers to get them to fit think i had to take about .004 off the washers to make them fit nicely. im also running a reed block so i added windows and lightened the piston a bit.

the plating on the cylinders suck but that didnt stop me from trying to make some extra pony. im on my third motor build with the km 30.5 now.
Click to expand...

Do yours have the free port issue. First Dan acted like he didnt know then he flip flopped and said most of the Km motors are like that. I will run this one till it blows up but I wont be buying a replacement. Its a shame too because it really has a lot of potential with the huge ports and the roughed in eyebrow ports.Wouldnt need a ton of work to make it rip if the piston skirt was a smidge longer.
 
I did a quick search. rovan has a kit for 29cc without a crank. The 30.5cc kit comes with a new crank so that leads me to think you do have the 2mm stroker and its not compatible with the 30.5 kit, hence the included crank.
 
30.5 cc engines do have the +2mm crank shaft - Unless the KM is not catagorizing the engine correctly, which could be the case as well.
I would look at a +1mm to see if that would allow the port to stay closed & see how that would work.
Lots of options in these little engines, but messing around with a sub par build like this seems like a waste of time and money to me.
It is your project though, and as long as you are happy doing it, More power to you !
 
rovanmadlunatic said:
I did a quick search. rovan has a kit for 29cc without a crank. The 30.5cc kit comes with a new crank so that leads me to think you do have the 2mm stroker and its not compatible with the 30.5 kit, hence the included crank.
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I have been doing a bit of research and it is hard to find exact spec's on the Rovan motors. Here's what I think I have figured out with ALL the different brands of engines.

Most of the engines orignally came with a 28mm stroke and a couple of different bores (IE: 23cc and 26cc)
Over time the engines got bigger and in order to make more cc you either increase the bore or stroke or both.

If stroke is increased and everything else stays the same it will hit the top of the cylinder. There are 3 solutions: 1. shorten the rod 2. Make the cylinder taller 3. Move the wrist pin higher in the piston

If the bore is increased you can leave everything else alone and just change the internal diameter of the cylinder and the diameter of the piston (easiest way for the manuf. to make bigger engines).

I believe there might be a misunderstanding of the word "stroker". A stroker is taking an engine and modifying it to have a longer stroke which would give more CC. Some hobbyist have done this to their engines. Some of the engine's being produced by the factories are just duplicates of what the hobbyist were doing. For example a cy29 motor is a 30mm stroke engine which is +2mm stroked over the original design of the cy23.

I have been unable to find out if ALL of the factory rod's are the same length on the cy, g, ky, rovan, and zen motors (excluding the new 32cc and above motors). If the rod's are all the same length then basically I believe all motors with 30mm strokes should allow for us to choose a 36mm 30.5cc cylinder and upgrade our cy29 or cy-f270 to 30.5cc with just a piston and cylinder. Caveat is that we cannot use the g290rc cylinder because the crank in that motor is only 28mm stroke so the cylinder will not have the extra 2mm of height built into it.

Am I thinking correctly on this???

Below is a nice chart that funbob posted (I added motors on the end):

32mm bore + 28mm stroke = 22.5cc cy23rc g240rc
32mm bore + 29mm stroke = 23.3cc
32mm bore + 30mm stroke = 24.1cc
34mm bore + 28mm stroke = 25.4cc cy26rc
34mm bore + 29mm stroke = 26.3cc
34mm bore + 30mm stroke = 27.2cc cy-f270
35mm bore + 28mm stroke = 26.9cc cy27rc
35mm bore + 29mm stroke = 27.9cc
35mm bore + 30mm stroke = 28.9cc cy29rc
36mm bore + 28mm stroke = 28.5cc g290rc cy290f
36mm bore + 29mm stroke = 29.5cc
36mm bore + 30mm stroke = 30.5cc cy31rc
 
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