doing a top end

skid jackson · #1 05-12-2008, 09:37 PM

06 300

getting ready to do this for the first time.

When you pull the jug do you have to pull out all the power valve stuff first, or can you pull the jug with that stuff in place and remove it when you've got the jug on the bench??

Also the the nut that is on the head that sits to the right of the front engine clamp does not have enough room to fit a socket in there. the mold for the cooling hose fitting gets in the way. I ground down a twelve mm box wrench to get it out but that won't really work with torque wrench, .... guess I could get a socket welded to the wrench. Can you grind a socket down some and also grind a bit off the head. or does taking adremel to that section of hte head sound risky

Brian VT · #2 05-12-2008, 09:42 PM

See here: http://www.gasgasrider.org/forum/sho...highlight=13mm

eff · #3 05-13-2008, 05:34 AM

All you have to do to pull the head is take the little nut off on the righ PV actuator (or whatever it is called) and pull the arm off of it. Some guys have had problems with the post breaking off so it is recommended to hit it with a torch and replace it with a new M5 nyloc nut.

I had to gring a 12mm wrench too. You can easily make a torque adaptor as you have said. I should have broght my head into work and machined the area a little more. A Dremel may damage the head bolt seat if you are not very careful.

skid jackson · #4 05-13-2008, 10:25 PM

I posted some pics in the photo section. take a look at them and let me know if you see anything to be concerned about. ring end gap is between .38 and.35mm. service manual says it shoud be between .8 and .5 ... whats up wit dat??

are those vertical lines in the jug anything to be concerned about?? you can't feel them with your finger. is that from the piston skirt moving around??

skid jackson · #5 05-14-2008, 08:48 PM

ok so I'm trying to take my pv assembly apart to clean it. I'm at step 8 on uwe hales instructions, "grab lever bolt by the head and pull out the rightside pv assembly" I'm pulling like a sumbitch but the fugger ain't going anywhere. Whats the trick to getting this thing out. I'm guessing it is glued in from the spooge, do I have to hit it with some penetrating oil?? A little heat maybe??

per gofasters ... take a punch, reach inside the exhuast port and tap it out. works quite nicely

skid jackson · #6 05-21-2008, 08:52 PM

ok my top end saga continues ....

I wasn't paying attention to the printing on the rings when i installed them I got the first one right and the second one wrong. when I went to slide the piston back in (from the bottom of the jug)the fugger went in a bit but then would not budge. In fact I had to use a wooden dowl to knock it back out. Was this caused by the upside down second ring???

naturally the nicely oil piston slipped out of my hand and went for a roll around the bench top. It's got knicked on the top edge so now I don't believe it is usable. the new piston they sent out is a B, the old one is an A. There was not a lot of wear on the original rings. The B piston seems very very very tight in the bore, but will go in. Still seems like it could be tight enough that when things heat up it might bind/seize. right now I'm thinking I'll need to order another A piston. Of course that means no riding over the holiday weekend .... or .... shoe horn the B piston in there and go rip it up!! ...or blow it up ....

anyone know what the deal is as far as putting a B piston in what I would guess would be a close to stock bore

hmm ok I went out and measured both pistons.
The A was about 71.35 mm While the B was 71.4. It was kind of tough to get a consistent number on the A with my $40 digital calipers. The B was spot on though

I could not get a good read on the bore as the caliper does not go that far down. What I did get was 71.3 at the top. Which doesn't make sense as the 71.4 B piston managed to slide into the bore.

I oiled up the b piston and slid it into the bore (no rings) and there seemed to be room for it to move around.

hmmm what to do ....

PEB · #7 05-21-2008, 09:24 PM

I did the same thing with the rings last time I did a top end except I had buttoned it all up before I realized I had not checked the orientation of the rings. I tore the whole thing apart and sure enough one was in upside down. This was after I over ground one of the rings trying to set the end gap resulting in me buying a new set. It did not seem to hinder the piston sliding in the bore. From what I understand you can not accurately measure the bore or piston with simple calipers, you need a special three pronged measuring tool. As far as the nick goes I would guess that if you deburred it it would be fine as long as it is a small blemish. I would be more concerned about running to large a piston in your cylinder, how old is the bike and how many hours are on it? Good luck and don't rush. One last suggestion if it applies, I have been trying to drink my wobble pops after wrenching lately.

Paul B

skid jackson · #8 05-21-2008, 09:47 PM

06 300 70 hours

I'd really like to know why It would not go in. It came out that way just fine. I was thinking maybe the rings went over the pins but they were where they were suppose to be.

PEB · #9 05-21-2008, 11:43 PM

70 hrs, I would put the new rings on the old piston, assuming they are the same brand and ride this weekend. Put another 70 hours on it and then get another piston. But remember I am a frugal, hack mechanic. Perhaps someone else will chime in.

Paul B

stay_upright · #10 05-22-2008, 05:43 AM

You cannot usually accurately measure bores or pistons with digital calipers. Have a look at the accuracy of the calipers norlmally on the side. Also pistons are barrel shaped widest around the middle portion of the skirt - this is to allow for thermal expansion of the top of the piston (which gets hotter than the skirt). You probably cannot hold the calipers accurately enough at 90 degrees to the piston to get an accurate measurement even if your calipers were of the accuracy you need. For the bore you need a 3 prong bore measuring device for similar reasons plus the need to accuralely centre any measuring device.

When you get your new rings/piston done measure compression with a compression tester and benchmark this. They later if you wonder if your rings are worn just check the compression.

Measurements of my KTM pistons and bore showed my pistons had very very little wear (practically negligable) and the choice of A or B pistons was much more important than if a piston was worn. I would also guess manufacturing tolerances may be larger than the wear amount. Also the Nikasil bore was worn to 1/2 the KTM spec in about 8 years so nothing to worry about there. For visible marks in the bore which you cannot feel I would not worry about them in terms of them compromising engine performance though bear in mind it means that something has scraped the bore - usually there are corresponding piston marks though it could be something jammed between the piston/bore - anyway these seemed quite common and did not affect my engine.

As mentioned above with the compression meter I use this to decide when to replace rings etc rather than number of hours - seems like a smart way to do it and will probably extend changes on the 300 a long time as they seem to have very little wear.

At what point did your replacement piston get jammed in the bore? i.e. at the skirt or ring area? - again bear in mind the piston is barrel shaped would the top fit in first? Piston selection A or B seemed like a black art on the KTM since no-one accurately measures bores and pistons and even when I did trying to get a spec for minumum clearance was difficult. Also the shops advice (speak to some-one who replaces a lot of pistons) was that after the first ring change you coul dfit the bigger piston on a KTM but again as I remember manufacturing tolerances seemed to play a much bigger part the relative tolerances. At least if you put the same sized piston in you know you are safe though if most people fit the bigger piston you should be fine with that.