Hello,

We are having some issues with our 250cc aixro kart engine.. for some reason one sideplate gets quite deep grooves in it, and the other side remains in top notch shape.

Does anyone have a clue what can be the source of this nasty grooves? as there can be seen on the second picture, the two-piece apex seals are slightly too long causing the small tip not to touch the rotor housing.. the groove sideplate was on the side of the long piece of the apex, so not on the tip side..

the apex seals are made of some ceramic substance that it's so hard that we didn't find a tool yet to cut them shorter, altough now it's winter we have time to sort that out..

the engine is running on E85 and before the summer I made a the smaller bridge port style port at the opposide side of the main side intake port, altough it doesn't change the overal sideport timing.. at high rpm is has a dashpot operated peripheral intake port

I forgot the to mention the sideplates are just cast aluminum without any coating, but during this winter we'll have them coated..



Ruben

 

this same problem is mentioned in the yamaguchi FD book. in developing the FD engine, they had the same problem wearing the one side plate.

they decided that the rotor was flopping around too much, so they approached a fix from a couple directions. after asking the racing dept who were making more power with better reliability

1. they changed the bearings.

2. they increased the oil pressure.

3. they also increased the clearance between the side housing and rotor, IE side clearancing

its kind of weird its not an issue on the mazda engine @200hp, but it is @250!

 

Interesting, do they also explain why only one sideplate has this wear? Whats also curious is that the rotor itself doesn't seem to have made the groovesin the plate, the scratch tracks follow the contour of the apex seals and corner seal.

The clearance of the main bearing is 0.03mm, normally 0.04mm is preferred clearance.. I'll have a look in side clearancing the rotor to see if it can be a solution to our problem..

Thanks for the good info

Could it also be a side of effect of inproper balancing of the rotor/rotating assembly?

 

I wonder if the rotor gets a thrust load from one side from the stationary gear and that is why you get wear on one sideplate.

This roller bearing crank engine cannot really decrease main bearing clearance nor raise oil pressure to help stabilize the rotor.

I am thinking that leaves larger rotor to sideplate clearance, balancing and coating the rotor side and plate so that momentary contact does less damage- all of which you mentioned.

 

I measured the the rotorhousing, it's between 68.20 and 68.04 mm, the rotor measures 67.88, so we have around 2-3tenth of a mm side clearance.. what is the recommanded rotor side clearance for a 12a or 13b which is spinning 10-11krpm?

What suprises me is that if you look at the rotor, it doesn't have any marks of contact with the sidehousing, the track is just as wide as the corner and apex seal.. the damaged housing is at the long side of the apex and the side of the stationary gear

 

the book actually says " ...and scraping off the oil layer. the corner of the apex seal starved of oil and finally stuck within the grooves"

so it does sound like the corners of the rotors get damaged too.

not sure off the top what the side clearance should be, but you can look it up for the rx8, as its standard on those

 

You get the same mark when running resurfaced irons with FD corner seal springs. The spring tension forces the corner seal against the now softer iron and the sharp edge cuts into the surface. Since your rotor is not touching it's not a side clearance issue, and if the apex seal was too long there would be a mark on the opposite surface also. So it appears it's the corner seals. You probably can't reduce spring tension so the alternative is to file a small radius on the corner seal edge. This will stop them digging in. It could be partly a thrust loading issue, but the fact remains it's the corner seals doing the damage.


Edit: looking at the pics again it does look like the apex seal it touching also. Weird

 

The grooves look a lot bigger than the corner seals are. Just saying but i dont know.

Really interesting engine. Ive seen 50cc 1 rotor go-kart motors before but never this one. God would i love to drive one of these. Used to race yamaha kt-100 karts before but never driven a rotary kart. : (

 

very interesting !
looking at that i think rotor land clearance on that side of the rotor is out of spec
or some thrusting issue away from the stat gear,, or both

check the equivalent of rotor land projection on each side of the rotor
-- in a mazda rotor ,, the land is often pushed out when bearings are installed or over revved and can be fixed with a hefty tap

also see if its possible to shim out the stat gear if there is evidence it has bottomed in the rotor gear

 

I was reading up on the Aixro a bit to try to figure out the rotor gas sealing and intake path to see if your additional port could be causing the wear problem.

Are you taking intake temperature readings as recommended at the transfer port where the plug is? Are they still in the recommended range?

You are running E85, which will have enhanced cooling properties as a greater volume of fuel is required...

BUT the fact is the port you added bypasses the cooling and lubrication scheme of the rotor and all the moving parts.

The entire intake charge is supposed to go from the one side housing, through the rotor/e-shaft too cool/lubricate it and into the port on the opposing side housing.

Except for when the aux peripheral port opens (for which reason they say do not use full throttle for more than 10 seconds at a time as the intake/ rotor cooling temperatures soar).

Is it possible due to the added bypass port you are running too high of a rotor temperature sticking the long part of the apex seal or that corner seal in the rotor groove?

 

Good info guys

What I don't understand if that if the spring tension would be rather high, why the other sidehousing is still in mint condition? the start geat van be shimmed out, but the cannot be bottomed out because the damage is at the side of the gear, so the gear should have pulled the rotor..


@PDF, the apex seals are too long, if you look at the second picture you can see the track of the small tip apex seal that didn't touch the rotorhousing,which I think can only happen because the tip is puched downwards by the too long apex..

 

You can be right yes, but last time when opened the engine up to replace the rotor bearing it had exactly the same grooves in that sidehousing, this was before the additional port was added and before we switched to E85. then we just resurfaced the damaged housing and I added the port as I expeced when running on E85 it would not be a concern.

Unfortunatly we didn't run the transfer port thermocouple as out sidehousing isn't drilled for one. in the future we will run one for sure to see what is going on.

We did measure water temperature and in fact is was running cooler (60°C) with a smaller radiator than the other engine running on gasoline with a bigger radiator, which I think comes from the E85