G’day guys, time to sort this once and for all so I’ve been at this engine for a little while now. When i first got it, it was smoking at idle after it had warmed up. So i replaced the rings and honed the cylinders replaced gaskets etc... Put it back together to fire it up and it idles, but with throttle it dies and is smoking a little out the exhaust (Alot less then it was). Took the plugs out and they were completely carbon fouled and some had oil on them. Engine had max compression of 120psi on certain cylinders. All others were below that. I remember flipping the head upside down to clean it and most of the buckets fell out and not thinking with my brain, i cunningly put them all back semi randomly. Timing was also 1-2 degrees retarded as I couldn't get it perfect no matter what i tried. Could this be the problem? I have also put a zeal exhaust on it. Could this also affect the performance. Bit of an essay right here, so I do apologise
Beware that compression on these small engines should be done with throttle at wide open and slides lifted (or carbs removed) and some testers are not accurate in such small engines. Based on your descriptions the head will need reconditioning, meaning all 16 valves out for a clean up/cut/grind including the seats. New valve stem seals too. New timing chain and tensioner springs, and finally check and adjust all valve clearances. A carb service might be needed after all that but see how it goes, the 2KR carbs are less troublesome than the 3LN ones. 3LN is a more refined engine with revised pistons, rings and lighter valves plus the EXUP exhaust. If yours is non-EXUP the zeal exhaust should suffice. If it is EXUP then your bike is most likely a 3HX model, which is just a 2KR with EXUP fitted.
My advise, go back and set valve clearances properly before worrying about compressions, and how have you seated/bed in the rings to the bores? What were the ring gaps in the unworn part of the bores? Again don't worry about compression numbers until the rings seal and the engine has done about 100Km.
+1 for valve clearances and if you do need valve stem seals, I recall that @Mike Green got some from aliexpress IIRC that were for 4mm valve stems, his valves are 3.5mm stems, so he may have a set already in NZ Carbon on the plugs from excess fuel is a 3LN trademark, but I cannot recall there being an issue of that nature with 2KR carbs, it someone has been at the carbs previously, then the fuel level in the float bowls can be checked AND if necessary the float heights adjusted
Awesome thank you so much Am putting the head back on today and doing the clearances like i shouldve done before i pulled it apart Probably wont hurt to do the seals as well huh while the head is off the engine. It is just the non exup model so my thought was that it'd work but it’s just a process of elimination I guess
Cheers Ruckusman! Are they 4mm valve stems on the stock engine. May have to go invest in some right away. And do you have the shim sizes by any chance off the top of your head or does that really depend on the engine and it’s wear and tear? When the carbs are back I’ll set the float heights properly with clear tube against the carbs measuring the fuel level. Saw a diagram on a previous thread?
Cheers murdo! I think you are right there aye. Will put new seals and do the clearances, how ever I’m still worried about the timing being a little off. Would this make the whole engine run like a dog? I have really only just put the new rings in. Only idled it a few times and a run around the block. Havent given heeeaps of gas. Maybe just less than half revs.
2KR runs valves with a 4mm stem - @Mike Green ordered a set, for a 3LN with has a 3.5mm stem, from aliexpress I think and they sent 4mm ones - so he may be able to sell them on to you - he's in NZ which makes it easier Shims you will have to check each individual one, they are 7.48mm diameter - they will vary - the thickness is etched/printed on them, BUT if that has been face down on top of the valve it may not be legible, so best have a micrometer to read them. Usual process is check clearance, see what you've got and then figure out the swaps, they will reduce in thickness, and order what you need BTW it might be worth checking your engine number to be certain that it's the original engine if there's any doubt - valve stem diameter is one difference between the versions https://www.2fiftycc.com/index.php?threads/fzr250-model-descriptions-and-identification.6668/ and https://www.2fiftycc.com/index.php?...zr250-bodywork-frame-engine-carburetors.3469/
I do have new Aliexpress 4mm valve seals. You can have them. If you are in Auckland we might be able to do swaps for the shims if you need ones that I have. I don't have a full range, just a few around the sizes that I'm using. I also have 2KR pistons. As far as I can tell they don't seem to wear out but I suppose if you neglect them enough anything is possible. Just in case you end up needing a piston for some reason. With the valve timing these things have they are never going to pump much of a compression ratio at less than idle speeds. On that note as long as the timing isn't out by a whole tooth it will be as close as the factory thought it needed to be. I've slotted the cam sprockets and timed mine as exactly as possible but only because of the other things I'm doing and I didn't want anything else affecting anything and also to know exactly what I was starting with.
Awesome thank you mike. I will see what i can come up with for ya Unfortunately I’m in matamata so a little ways away. The valves are 3.9-4mm thick so would they still seal alright? Yes the timing was getting to me as it would never be perfect. When the tensioner took the slack it moved the whole thing. No that the engine is out hopefully i can get it perfect, if the chain isnt too stretched that is. Also how would you go about cleaning the valves. A lot of carbon build up on them and it’s got to mint going back together. Saw some people get out the scotch brite and sand paper and i said to myself, surely not?
The valve seals are for the valves with 4mm stems so will work fine. I cleaned my valves with emery tape before I sent them to NZ Cylinders with the head. I found that leaving them to soak in engine cleaner for a few days seemed to soften the burnt on carbon. NZ Cylinders did the valves for me. They cut the seats and ground the valve faces. They made custom tools to do the job as they had nothing small enough. A few compromises were made in the end but it seems to work OK so far. If you have the valves out make sure you check the spring installed height. EVERY head I've checked so far, the springs have been installed overheight by about 1mm which is huge on these little things. No wonder they have a reputation for dropping valves and valve bouncing.
Awesome will give that a go tomorrow, see if we can get some of that carbon off. They sound like a good bunch might have to look them up. Get this head done. How much did that set tou back if you mind me asking? Funny they had to make custom tools. Size of the parts in this engine are just so small. Scares me to imagine them at full bore. How do you install the valves a bit over? I always thought they went back in one way. Is it to do with the collets not seating properly? Or does the spring stretch a little?
The valve springs are fitted between a spring base at the bottom of the spring bore and the retainer at the top of the valve. It isn't something that can be screwed up just by putting it back together wrong using all the original parts. The problem is that the original parts are incorrect. I made new spring bases that were 1mm thicker than the originals which obviously compressed the spring 1mm more than original. I've checked a few 2KR and 3LN heads and all the valve springs I checked were about 1mm over the correct installed length. It was pretty consistent. I checked and double checked and triple checked. They were all the same. Quite surprising considering the precision of the rest of the engine. The head cost a bit shy of $1K. Not cheap, but when you can't use standard tooling and it all has to be fabricated it starts adding up. To be honest I don't mind paying to have the job done right. I've been very definite about what I want with getting other work done and been disappointed many times with the end results. Not this time
I see. This is a slight concern.) Could this cause any short or long term damage over time if i put it back together using all original parts? Cleaned up of course. Plan on eventually selling it so she’s got to be mint. Bit funky how they could get it not quite correct from factory. Weird stuff indeed And yes 1k is understandable considering all they did. Least ya know it’s a minter! Do you have any photos of your fzr? and hey just wondering how much you wanted for those valve stem seals? Only when it suits ya though. Damn exhaust gaskets are hard to find around here too. Is there a sheet where you can make them yourself?
You can have the seals. Vesrah have an exhaust gasket that fits nicely, VE-3001. Photo below and link to it running on the dyno. 2nd run just taps the rev limiter at 18,000 at the end.
If the springs are installed "over-height" they will not be applying enough force on the valves to keep them in proper contact with the cam lobe at high revs. People complain about bikes not revving properly all the time and it's sometimes because the valves start floating. If you push it hard enough once that starts happening it can get really ugly really quickly. If you have it apart measure it. It isn't too hard to fix if it's wrong. A simple 1mm washer for example under each spring base might be enough. I made new spring bases and had then nitrided but that's me.
That! Is one naughty motorcycle. I have to say great job. Certainly looks the parts and sounds like an absolute missile! How many races have you done with with it. Top of the class surely? And hey cheers for that i really appreciate it. I could pm you my address and sort some shipping? If there is anything you need that i might have just give me a bell. And cheers again been looking for exhaust gaskets for a wee while now. Bit of an odd ball size.
Now that sounds like a recipe for catastrophic failure. Definitely worth a check while they are out like you say. Will give cleaning the carbon off a go tomorrow hopefully without damaging anything and should be alright. Do you know the thickness of the spring base, or what it is meant to be? If they were under more tension, could it damage the sealing surface of the valves as they would be snapped shut harder? Or am I hallucinating
The idea is to get it right. I haven't increased the valve seat pressure from stock, maybe a very small amount. I suspect the small valve stems and being older parts would possibly not like excess pressure. I can't remember the actual numbers but the new spring bases were 1mm thicker than original which got the spring installed height right on the money. Spring tension will not cause the valves to snap shut. The correct tension will apply enough force to keep the valve stem, shim, and tappet all in contact with the cam throughout it's travel. If the spring installed height is too great the spring tension will be less and the valve seat pressure too low. The effect is that the cam pushes the valve open OK but after the nose of the cam has passed there may not be enough pressure applied to force the valve and tappet etc to follow the profile of the cam. That is what might cause the valve to "snap" back on the seat, rather than being lowered gently by the cam. The other thing that might happen is with the valve not being where it should be is that there could be contact with the piston on overlap. The FZR valves are very close to the piston on overlap so it is possible. I saw it on my exhaust valves in the other engine with nice clean spots in the valve pockets. Here's a couple of numbers for you - the seat pressure on the FZR250s is 25lbs. My mate has v8 race engine heads with 600lbs seat pressure. That's on the seat. On the nose it's absolutely huge.
