Boring a 2005 EFI 900 King Cat (Stock M1000 Cylinders?)

507Sledz · Mar 8, 2014

RE:

Well I got my motor out this afternoon, I figured out a piston ring broke, ended up on top some how and destroyed the top of my piston and head. Some metal fell in the crank so we are going to look over that really good make sure its top notch before We put it back in. I also purchased a wildchild post today with a slightly more forward bend then what he originally makes. Figured I might as well throw that in sense my motor is already out.

Still havent figured out what type of bore kit I want to do. or just keep it a 900 and put High Comp heads on it.

tweeds · Mar 9, 2014

Have u thought about the cutler 1000? 2 years on one with nitrous no issues

Idcatman1 · Mar 9, 2014

Anyone have any ideas why an ununmodified EFI would seize up?

Several possibilities,

Air leak in either the throttle body rubber mount, or in the crankcase seals.

Oil pump failure, oil pump cable failure, water in the oil freezing and blocking the line, oil lines come off or break.

bad gas.

electrical component failure.

Probably many more.

Is an un un modified the same as a modified? Sorry I couldn't resist.

timber76 · Mar 9, 2014

Dang that's what I get for typing on my phone...funny. I was just curious so I can avoid any potential problems with my machine. Sounds like the OP's ring failure wasn't preventable. Bummer...

507Sledz · Mar 9, 2014

RE:

Well I went to clean up my crank today and looked over my motor some more and found out the other piston was also broke. That metal piece you see laying on my piston was just sitting between my rings, I could hardly see the cracks on each side. I actually had to pull it out of the piston my self. The interesting thing is that my jug never got scored or shows signs of any wear. But I would be willing to bet the same thing happen to my PTO side jug and piston. But I most have rode it like that for awhile tell my ring broke then that metal part that came out of the piston ended up on top.

507Sledz · Mar 9, 2014

RE:

Tweeds,

What exactly is the Cutler 1000. Is it a kit, like jugs, pistons and power valves? or is it just pistons and do I need to bore my jugs to fit the cutler pistons? I would love to get my sled to a 1000cc or 1050cc. I don't want to go anymore then that. and I don't want to do anything less then actually 1000cc pistons. If I can't find something with actual 1000cc pistons then I'll just keep in a 900.

Do you have high comp heads on your cutler 1000?

Thanks for the helpful info!!

mike_s · Mar 9, 2014

What RPM are you running your engine at full throttle? I am wondering if you could be running into ring flutter there. An engine with a stroke long as these shouldnt be reved real high, i forget but i think cat calls for something like 7500? When a long stroke engine is reved higher than its design tolerance, the rate of piston deceleration at the top of the stroke is enough to cause the ring to slam into the top of the ring land. Now, because of the fact that compression pressure is primarily responsible for maintaining ring pressure against the cylinder wall, now you have 2 problems, blowby and the chance for the ring to now slam into the botom of the ring land, caused by the blowby and compression pressure rushing past the ring. In extreme cases, this can cause irregular cylinder wear, wear and breakage of the ring lands (as you have there) and worst case scenario can actually cause the nikasil to separate in the cylinder right around TDC.

507Sledz · Mar 9, 2014

RE:

mike,

i believe my motor does run at 7500 at full throttle. maybe 7800. but im pretty sure its 7500. what would cause my motor to over rev and slap?

thanks

mike_s · Mar 9, 2014

If your clutched to run where the factory indended then chances of ring flutter are low. Your piston breakage could be caused by a number of other things, as well. Defective pistons (unlikely, as they both failed in the same mode), piston wear (depending on miles), plus many more. Could be that the port chamfering was done poorly, causing the rings to want to catch the exhaust port. This could cause both of the failures you expirienced. I suppose its all a bit moot at this point, as you are rebuilding anyways, but at least you will have an idea of things to watch out for as you reassemble your new engine, to prevent it in the future.

507Sledz · Mar 9, 2014

RE:

Mike sounds good! thanks for the helpful info.

Tweeds,

I just looked the cutler website. https://www.cpcracing.com/instructions/ right? I don't see a bore kit for my sled. But I did look at a bore kit they do offer and it was $3500!!!! thats what I picked my sled up for haha. approximately how much did your setup cost?

thanks

kiliki · Mar 9, 2014

I have done a few of these and if you must have " 1000 or better" you are just spending your money on a bad mind set. the 975 is the clear winner for the money with stock (cheaper) pistons.
as for ring slap in the above post call arctic cat and tell them the m8 motor that runs at 8k is in need of a upgrade, stroke doesn't matter when they all go up and down. now if you suffer deto on the larger piston this is now an issue for ring land breakage. I have run this motor on twins at 8100 all day long as many of the two strokes today run. cat motors hold up well even on the bb side the tuner is the problem in most cases.

efi is a set of open tuning and is set for known fuel, air and displacement. if you change the displacement now the air and fuel need to be increased to match the displacement thus making a larger motor run lean on the same fuel map.
in the auto world a closed loop is used with a o2 guage to give feed back on the ratio of fuel to air, the ecu will add fuel to hit the set point and make the fuel mix happy what ever the displacement is up to the fuel systems limits.

as each run "efi" electronic fuel injection the closed loop V the open loop are completely different

76

mike_s · Mar 9, 2014

If i may, i think you would enjoy the 975 as mentioned earlier. I ride with the idcatmen, and i can attest, that engine is one to be had. Personal expirience, their mild mannered, manageable, quiet, reliable pump gas 975's would run just as good, to (usually) a little better than my ratty, noisy, hard to handle, peaky, slightly unrealiable full-mod everything-you-can-think-of high compression (175 PSI) 860 triple running on 105 octane. To say im impressed with the reliable performance doesnt say as much as me (die hard polaris guy) gearing up to replace my mod ultra motor with one.

Plus its not $3500 to do one.

mike_s · Mar 9, 2014

kiliki said:
I have done a few of these and if you must have " 1000 or better" you are just spending your money on a bad mind set. the 975 is the clear winner for the money with stock (cheaper) pistons.
as for ring slap in the above post call arctic cat and tell them the m8 motor that runs at 8k is in need of a upgrade, stroke doesn't matter when they all go up and down. now if you suffer deto on the larger piston this is now an issue for ring land breakage. I have run this motor on twins at 8100 all day long as many of the two strokes today run. cat motors hold up well even on the bb side the tuner is the problem in most cases.

efi is a set of open tuning and is set for known fuel, air and displacement. if you change the displacement now the air and fuel need to be increased to match the displacement thus making a larger motor run lean on the same fuel map.
in the auto world a closed loop is used with a o2 guage to give feed back on the ratio of fuel to air, the ecu will add fuel to hit the set point and make the fuel mix happy what ever the displacement is up to the fuel systems limits.

as each run "efi" electronic fuel injection the closed loop V the open loop are completely different
I appreciate Mike s input about ring slap but his knowledge is less than his age in CM. you need to look back to the catmans info as these guys have forgotten more then mike has yet to learn.

76

Absolutely no signs of detonation on the piston domes, or the heads, judging by the pictures he posted, glad youve had good luck overreving an engine, and thanks for the cheapshot!

kiliki · Mar 9, 2014

no over rev as each pipe set and displacement will require a different RPM to produce peak power.
as for stock yes most guys over rev the stock set up.

507Sledz · Mar 9, 2014

RE:

Killiki,

There is a guy on here that wants sell me some cutler 1150cc piston, jugs and power valves for $500. But I feel that is a little "over bore" haha!! If i do a 975 bore what jugs do I use? or do I just bore my 900 cc jugs?

thanks

mike_s · Mar 9, 2014

Bore your stock cylinders to fit the pistons out of an m1000, and use a cylinder spacer to make up the piston height difference.

507Sledz · Mar 9, 2014

RE:

Thanks for the info Mike!

So once I bore my jugs to fit m1000 pistons, what else do I have to do to my motor to make sure everything runs perfect! such as power valves, heads?

1. and can I run High comp heads on the m1000 bore?

2.Also will this effect the durability of the motor? sense I will have smaller cylinder walls?

3.will my computer be able to handle this bore?

4.do you know off the top of your head the HP gain on 75 more cc?
will i be able to notice a difference when I go to ride it again with a 975cc?

mike_s · Mar 9, 2014

507Sledz said:
Thanks for the info Mike!

So once I bore my jugs to fit m1000 pistons, what else do I have to do to my motor to make sure everything runs perfect! such as power valves, heads?

1. and can I run High comp heads on the m1000 bore?

2.Also will this effect the durability of the motor? sense I will have smaller cylinder walls?

3.will my computer be able to handle this bore?

4.do you know off the top of your head the HP gain on 75 more cc?
will i be able to notice a difference when I go to ride it again with a 975cc?

Heads and valves will have to be matched to the bore, as is the case any time you change the bore size of any engine. The ecm will not know any changes have been made. As kiliki stated earlier, it is an open loop system and operates on a set number of perameters. If any of those perameters change (displacement, exhaust design/flow, intake flow, injector size ect) then you will have to find a way to compensate for it. Fuel control box should suffice, however i am not intimately familiar with the cat injection system. I dont think durability will be an issue, i have ridden with the catmen's 975's numerous times, and have never seen one fail, but they will have more to say with their expirience with theirs. I cant speak of the gain, as ive only ever ridden the 975. But i will tell you, its no slacker in my oppinion.

Idcatman3 · Mar 9, 2014

Everyone settle.

Mike actually has a fair amount of experience with Cat 900 engines, although much of it is second hand. He's been around our 975s for years, and is looking at putting one in one of his sleds.

Fomoco is also quite knowledgeable about the subject, you can see his many posts in this section.

I don't see anything inaccurate that anyone has posted. Too high RPM on long stroke engines can be a problem. It's not always, but it's a risk, which is why the stock peak RPM on these is so low.

The M8 that runs a higher RPM is a much shorter stroke, (70mm, if I remember correctly), that makes a huge difference vs the 76mm of the 900. I'd do the math for you as to the difference in piston acceleration, but it's late and I don't want to.

Now cool the personal snarking and we may all get another couple guys running these engines out of the deal.

Idcatman3 · Mar 9, 2014

If you're interested in reading about piston speeds and accelerations, there's a pretty good write up here:
http://www.epi-eng.com/piston_engine_technology/piston_motion_basics.htm

Boring a 2005 EFI 900 King Cat (Stock M1000 Cylinders?)

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