Jump to content

My new YZ 250f

Recommended Posts

Get new valves ,springs and  seals and a set of rings . Do a light  valve lap with the seat and be done .

With Ti valves your not supposed to lap them though?

Share this post


Link to post
Share on other sites

Yes, do not lap titanium valves. If you get Stainless, you can lap the valve seats by using them. Or, if you stick with Titanium, you can lap the valve seat using the old soon to be disposed of valve.

Share this post


Link to post
Share on other sites

Yes, do not lap titanium valves. If you get Stainless, you can lap the valve seats by using them. Or, if you stick with Titanium, you can lap the valve seat using the old soon to be disposed of valve.

I plan on getting OEM so staying with Ti. I'm new to this, is lapping basically cleaning up the valve seat using a mild abrasive cutting paste? As the old valves are worn wont this give a different profile to the new valves? Do those valve seats not need cutting on a cnc machine? Is only done if there is pitting present?

Sorry for all the questions

Thanks for your help.

Share this post


Link to post
Share on other sites

I'm gunna send the head off to be recut. After having an experienced friend look at it I feel better knowing that it will be done properly. Also ordering a new cam chain and gunna re-ring while I'm at it. At least then I know it's done correctly.

  • Like 1

Share this post


Link to post
Share on other sites

I'm gunna send the head off to be recut. After having an experienced friend look at it I feel better knowing that it will be done properly. Also ordering a new cam chain and gunna re-ring while I'm at it. At least then I know it's done correctly.

 

That's the best approach.

Share this post


Link to post
Share on other sites

My new garage arrived today after a loooooong wait! However it's now up and I finally have space again to work. That is until I have to pull everything out again to paint the floor.....then make new benches.....and shelving......and panel the walls......and lights+sockets.... Oh well it's all part of the fun. I'm absolutely delighted with the size, it's 7 meters by 5 meters,  with 4 clear roof panels, a roller door in the front and sliding door in the back. That's my RM 125 that I'm currently riding. It's strange being back on a 2stroke, however I had a go on a friends KTM 150 at the track the last day and absolutely fell in love with it.

14183829_10210733949011177_1422584328188

 

Anyway I decided to take the cylinder off the YZF as I already have the head off. Here's what I found.... What do ye think? It's on the intake side, there's no matching mark on the cylinder strangely. Should I replace it? I'd rather not but if it needs doing I understand it should be done and will do it.  The crank feels fine zero up and down play.

14088491_10210733948771171_9417814796578

Share this post


Link to post
Share on other sites

Well just received word that my parts aren't expected to arrive on Friday the 9th of September. The machine shop I'm planning to send the head to, wants the new valves before he does anything. I was really hoping to enter my first race on Sunday the 11th. So I have a few choices:

A) Wait till the parts arrive and then send the head and parts off and miss the race.

B) Fit the new parts without sending the head away and race on Sunday

C) See if I can find a different machine shop that will do it without needing the new parts

D) Race the RM 125 (not overly keen on this as the track is extremely difficult on a 125 for a rider of my skill level as it has alot of elevation change and jumps out of corners which I will struggle to clear on the 125.

Opinions welcome on what I should do

Share this post


Link to post
Share on other sites

I usually work under the impression that if the work is worth doing, then do it properly. So I really wouldn't install the parts without doing everything first. That's how I operate, but to each his own. And I hate skipping races too!! So, going to the race on an underpowered 125, while it might be difficult, it most certainly will still be fun!! Casing jumps isn't any fun, but battling anyone on a 125 is almost always a Hoot!!! That would be my choice.

Share this post


Link to post
Share on other sites

I would make sure the work is done proper... last thing you want is a top end failure on all your new parts.. you've been so careful for the whole rebuild don't jump the gun for 1 race! Pin that 125

Share this post


Link to post
Share on other sites

I usually work under the impression that if the work is worth doing, then do it properly. So I really wouldn't install the parts without doing everything first. That's how I operate, but to each his own. And I hate skipping races too!! So, going to the race on an underpowered 125, while it might be difficult, it most certainly will still be fun!! Casing jumps isn't any fun, but battling anyone on a 125 is almost always a Hoot!!! That would be my choice.

 

 

I would make sure the work is done proper... last thing you want is a top end failure on all your new parts.. you've been so careful for the whole rebuild don't jump the gun for 1 race! Pin that 125

 

Yeah thanks guys I agree with that, I'm just go eager to get it done haha. Still it makes total sense to do it properly. 

I just rang another engineering company to see what they thought about the head and at one point the man said "the valves have to be ground in" to which I explained they were coated titanium valves. He didn't seem to understand the problem with that.... So I hope the company I am going to deal with understand that and don't ruin my new valves. 

I think I will race the 125, I'll be racing the C class anyway as it's my first race so hopefully I don't get totally dominated  :ride:  It's a shame the YZF suspension doesn't fit on easily lol, It's so much better. 

This thread has turned more to just my general motocross updates than anything but still :thumbsup: 

 

Just got the electricity box installed in my garage today and will hopefully be wired up in the not too distant future. Unfortunately I cannot do this myself as there is new strict regulations and has to be signed off by a license electrician :lame: .. 

  • Like 1

Share this post


Link to post
Share on other sites

Well I raced my first race this weekend on the RM 125. It was a one day event, with quads, sidecars and bikes. In my opinion they should have had it on 2 days as it a bit of a mess, there was 3 quad classes and then all the bikes ran together so A,B,C all raced together but were divided in the final result.. This made it a bit crowded on the track, I was the only 2 stroke there. I qualified 11th in practice out of 14 (in my class C). The track was super wet in practice with a very deep slippery top layer of muck, however before our first race this had been cleared off by the quads.

I finished 6th in the first moto which I was delighted with. In the second moto I spun out and got the bike stuck in a fence and as the races were only 5 laps (2.20 a lap) My race was over as it took ages to get the bike untangled. I was very annoyed as I was running 4th before I crashed. By the time moto 3 came around the rain had come down and it was a mud bath. On lap 4 as I came over the finish line jump disaster stuck. That sickening feeling of a dying 2 stroke, it bogged real hard and I managed to limp it off the track back to the pits. DNF 2 of 3 motos.... not a great start to my racing career. Hopefully I might be able to get some pics of the day

Edited by owainyz03

Share this post


Link to post
Share on other sites

Well I received my valve parts, you don't get much for €500 euro lol. 3 intake valves, springs, retainers, cotters and seals...I'll be sending the head off next week, I'm not sure if it needs work or not but it'll be worthwhile having a professional opinion. I didn't get my gaskets so I can't install the piston and cam chain unfortunately.

I tore down the RM 125 today, man I had the engine out in less time than it took to take the YZF rocker cover off lol, I miss the 2 stroke simplicity.

14317621_10210927954141184_1838059932723

 

14364671_10210927956941254_1261019064826

  • Like 1

Share this post


Link to post
Share on other sites

Well I was off this site for a while but I'm back now and figured I should give this thread a revive. I rebuilt the engine and got her running again. I'm not sure what happened to the pictures in this thread but I'll upload some new ones of the previous few months of track, trails and a bit of grass track fun. 

I checked valve clearances again today and they were still perfectly in spec:thumbsup:

I'll update this properly tomorrow with more details of the rebuild and riding time since then.

 

jump.jpg

track.jpg

trees.jpg

cork.jpg

corner.jpg

forestry.jpg

grasstrack.jpg

  • Like 1

Share this post


Link to post
Share on other sites

I went to change the fork seals after they blew out on my friends trailer :foul: Started disassembly only to find the damping rod doesn't return when pressed in like the video here. So looks like a full rebuild. Do the '11 forks still have the plastic free piston that can break? Mine won't retract out even as far as in the video on it's own

 https://www.youtube.com/watch?v=IBVwjH4hra8

 

fork.jpg

Share this post


Link to post
Share on other sites

Pulled apart the inner chamber of the forks today to find absolute carnage :banghead: Trying to source new free pistons over here will be interesting

 

 

free piston.jpeg

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:


×