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kato

edit: that atk WILL see the trails again

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putting a 94 atk back in business. Starting a new thread because the other one got started from a WTB thing and is in the wrong forum section. Here it is:

So i got the supertrapp disks from desertrunner (thanks man) and an oem xr400 carb (Kehin) from John (97XR400R) just to test, and I am basically getting the same symptoms: able to start the bike, it either surges or die slowly at idle.

I have found a decent priced ignition coil (mine is out of specs) in the UK, waiting on that.

A new thing today is that I did a compression test and got 65psi.. pretty sure that's less than 1/2 what i should be reading. I googled a bit and lapping the valves seem to be a fairly common thing on the rotax 604 engine. I wish i had a leak down device which would help me track down where the pressure escapes.

I also need to triple check timing, I think this could cause low pressure.

well, I'll keep updating this thread, feels good to share when you're alone in the garage trying to resurrect a beast...

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Well....start pouring the solvent in and check to see if the valves are leaking. :coolio:

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Well....start pouring the solvent in and check to see if the valves are leaking. :coolio:/>/>

it's not pouring out but barely sipping just a little (using rubbing alcohol). not sure if this could cause such a lack of compression.

cylinder looks good. i ll do heads first and tackle rings later

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I got in on this thread late, or I would have suggested a dry/wet compression test. Kick it over dry, take the reading. Then add a tablespoon of motor oil in the spark plug hole and take the reading again. If compression goes up significantly, then it's the rings, if not, it's the valves. And maybe a bit of both if the compression goes up so-so. :unsure:/>

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I checked compression with the e-start, not by kicking it, does that make a difference?

I dont see any automatic decompression device, only the manual lever

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I checked compression with the e-start, not by kicking it, does that make a difference?

I don't think so. Did you do a wet test also, by pouring a dab of oil in the spark plug hole?

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I checked compression with the e-start, not by kicking it, does that make a difference?

I don't think so. Did you do a wet test also, by pouring a dab of oil in the spark plug hole?

unfortunately I didnt do that..

since I am that far into it i will probably make a few calls tomorrow and find some new rings for it anyway.

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Here is some more entertainment:

Looks like the engine got hot on the exhaust side, not supposed to be a lip there (surface is smooth on the intake side) so possible leakage (no headgasket on this engine):

PHOTO_20130526_115927_zps3b4a1d4a.jpg

So i busted out the specialty tools, aka a $15 CL glass table that i picked up specially for the occasion and some 400 grit superglued on it:

PHOTO_20130526_180721_zpsb548115a.jpg

Looking much better, hopefully it seals better too:

PHOTO_20130526_180711_zps4af316e9.jpg

PHOTO_20130526_190637_zpsbc566c75.jpg

valve lapping station:

PHOTO_20130526_175335_zps36746749.jpg

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thanks Bob. I know its a special bike, today i found a custom made camshaft in it (by George @ Up-tite), I've got to get it going!

my problem with this is that friday i am moving to ramona to a much smaller place (I'm kind of like in that same position as the new guy who PM'd Randy, only not joking) and NO GARAGE. That's in 5 days. I don't know yet how that's going to work out but you will see (and hear) me on the trails one of these days I promise!

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pretty sure this morning I found what was causing me all these problem..

PHOTO_20130527_074318_zpse9feddfc.jpg

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Kato- that's perfectly normal...nothing to worry about...shove those back in there and ride that thing

Bwahahaha-

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:heh: ^^^^^^^^^^^^^^ yup, that could be a problem ^^^^^^^^^^^^^^^^ :heh:

Welcome to Ramona...it's an awesome place to live!

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Can't imagine it didn't take the cylinder with it.

Might want to measure it.

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Can't imagine it didn't take the cylinder with it.

Might want to measure it.

no lip on top, and i can still barely see the cross marks on the cylinder wall. looks pretty good.

it must have been cooked or/and oil changes have been skipped. First ring was blown as shown, second ring was stuck in the piston pretty badly too..

on wed I ll receive my new rings, then I ll do the hard break in method and we ll see what happens. I might install an oil cooler on this baby and definitely a temp gauge

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At least check (measure) the ring gap on installation- it's hard to imagine that level of ring damage without corresponding cylinder damage- unless the bore is really worn out.

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At least check (measure) the ring gap on installation- it's hard to imagine that level of ring damage without corresponding cylinder damage- unless the bore is really worn out.

Good idea will do, thanks for the advice Paul

Maybe the very fact that the ring exploded made the peices get inside the piston groove further due to compression, and therefore the cylinder wasnt hit?

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In addition to checking the bore and piston I.D. O.D. clearance (at room temperature it is typically tightest at the piston skirt bottom) you should be sure that the ring grooves are in ok condition. If the bottom side of your compression ring groove(s) is damaged you will never get good sealing and the piston will develop hot spots in any area that has excessive leakage past the compression rings, If the leaks are really bad it can cause the piston to outgrow the bore ie try to weld to the bore! The compression rings seal by being pressurised on the i.d. and are "pushed out and down" against the piston and bore. If the piston ring groove is trash all the gasses will sneak past the bottom side of the ring. (imagine an exhaust leak down the side of your piston) good intro to ring groove inspection

Something smells fishy as 99 ranch. My biggest question is WHY did the ring break? If the grooves were worn and big on a previous rebuild the rings could have been doing the nasty flutter dance inside the groove causing them to break. Another thing to consider is that some rings are extremely brittle, some are very malleable and easy to trash requiring a tool for installation, then there are the ones that can kick YOUR ASS and bounce off the floor and gouge your piston all while laughing at you. Very IMPORTANT.. once the rings are installed they should move freely in the groves, if they don't you have a problem. As for the no hone... It can depend heavily on the type of rings and the coating used on them. If you put new oil rings in don't be surprised if she smokes a little for a long time after the rebuild.

Keep up the good work!!!!

P.S. I find it hard believe there is no sealing ring of some sort on the head to cylinder interface. :hmmph: What's this clean area all about, is that evidence of a groove in the cylinder where a copper ring is supposed to be living?

ATK head.bmp

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At least check (measure) the ring gap on installation- it's hard to imagine that level of ring damage without corresponding cylinder damage- unless the bore is really worn out.

Good idea will do, thanks for the advice Paul

Maybe the very fact that the ring exploded made the peices get inside the piston groove further due to compression, and therefore the cylinder wasnt hit?

The ring was likely just bouncing up and down in the grove as the piston changed direction. That's why you should be concerned about the ring groove.

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I ll check ring grooves tonight after the kids are in bed, thanks for the advice.

been reading loads about it, broken ring happen.. all kinds of ---- happens really. this is obviously a bike that was ridden hard and probably raced at some point. The rare machined camshaft in it could confirm that.

Im confident that this fresh top end will bring it back to life for many more years of trail riding

And no, my engine has no head gasket of any sort (it does have a base gasket though). I spoke to rotax about it when i got the rings and they confirmed that. He did say something about a different piston (over bore maybe) needing one though. What you outlined on my pic is an indent in the head from the block, probably because the engine was over heated (hence the rings taking a hit as well maybe). The indent only happened on the exhaust side of the head, intake side was smooth. Here is a pic of the block mating surface:

PHOTO_20130528_193645_zps80e1b68c.jpg

PHOTO_20130528_193703_zpsde44eeb2.jpg

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John you are right, my piston is toast. The compression (top) ring groove clearance is good on the half intake side of piston, and way too much on the half exaust side. Looks like there was a high amount of compression in there somehow and it pushed hard on the ring which broke it and bent the piston grooves.

Thats also why the second ring was stuck in the piston: because the part of piston in between both rings is bent

Wow. Now how can something like this happen and what else should i be worry about?

Intake side of piston, looking good and parallel:

PHOTO_20130528_211457_zps6ab33e1f.jpg

Exaust side, pushed down in between top and second ring (the marks are from me trying to remove the stuck second ring):

PHOTO_20130528_211444_zps00b2322e.jpg

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When you reassemble, check for loose rod bearings, and check deck height. Make sure that piston won't touch the head, especially if the cyl. worked into the head.

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When you reassemble, check for loose rod bearings, and check deck height. Make sure that piston won't touch the head, especially if the cyl. worked into the head.

You mean visually check where the rod connect in the crank and wiggle around to make sure the bearing is ok?

To check deck height, manually turn crankshaft a few time to make sure valves dont hit the piston is enough?

also i located a tool that will let me measure the cylinder roundness also, will do that tomorrow

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If the rod bearings are too loose, or if the head is worn where the cylinder meets it the piston can touch the head when in operation and can lead to broken rings. A manual or Ron Woods would have a spec for deck height, the distance the piston sets below the top of the cylinder and/ or head.

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