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Discussion in 'Your 250cc Projects' started by Yetiburger, Oct 7, 2017.
ZXR discs have it but never seen it on an FZR
Wear limit for discs is usually 0.5mm from new.
You can figure out the original thickness of the discs by measuring either the inside or outsite lip of the disc where the pads don't run (and make it difficult to remove calipers when the disc is worn out) vs the thickness at the thinnest section - usually the centre of the pad surface.
My 2KR (single disc) had 4.5mm stamped on it. Can't say for sure what the 3ln limit is
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So I got the bike back on the road early January.
Its all legal with a WOF and Reg.
Also did a rider training day at my local track. bike did bloody well having the tits reved out of it next to race bikes and pennagales etc.
Have found I may need boots with toe sliders.
They let u on track with those?
I would have thought laces would be a no no
Good to hear the ol FZR did its business
Well gents the FZR served me well for a good while. I got it back on the road and got all my licensing done.
It was starting to smoke a bit but still ran great. To be fair I've let it sit for a good few months with crap gas and it still starts straight up and runs mint. Unfortunately once she's warm there's a not very nice sound coming from in the engine (too long dealing with an overweight under talented rider).
I thought hopefully it might have been the timing chain, but after talking to a couple of people I think it may be a small end, hard to tell. I'm thinking of stripping the engine down as it could probably do with some rings.
What are the main troubles I would have trying to get the engine back together?
No rods available?
valve stem seals, head gasket?
I would love to give this engine a birthday as I think its an awesome wee bike, and I love a project.
Any advice or experience welcome.
If I pull it apart I will take photos and keep you updated.
If the small end is going, then check Impex for rods.
Rod bolts are solved - Use Kawasaki ZXR250 ones - they're a great fit, tested personally - either Impex or Webike.
Timing chain is readily available.
I'm about to do some minute measurements of both new Aliexpress bearing shells and new OEM bearing shells - will do a writeup of the technique so that anyone can do it themselves with either a dial indicator or a micrometer.
Lots to decode [which I've done] as Yamaha don't give bearing material thickness for the various colours - BUGGERS!
Valve stem seals - aliexpress, make sure they're for a 3LN as the stem size is different [3.5mm] -v- the 2KR which is 4mm
Head gaskets are available OEM new ~$35AUD - any Yamaha dealer should be able to source one.
Reuse the base gasket, apparently the aliexpress one is not metal.
FYI I just got a set of 48.25mm O.S. aliexpress pistons and rings - they're quite good, need some deburring with an emery board but all other measurements are on spec [there are one or two differences in the which aren't of any consequence], including the rings which do actually have a 0.01 thickness difference between the the top and 2nd rings, which is on OEM spec.
I also purchased some aliexpress rings, 48mm [which I was going to use before deciding to go for a rebore], which all measured up on spec also.
BTW before you tear it down, how are your valve clearances?
Apparenty it is not uncommon for FZR 250's that have been raced, to destroy a bigend bearing, cylinder 4 as I recall. Well at least there have been several cases of this reported here. We have never gotten to the bottom of this because the owners never try to fix it or post photos and details. They just go and buy another engine and blow that one up. Now what was it about doing the same thing over and over again and expecting different results? Because it has always been cylinder 4, us forum sleuths have been suspicious about oil feed issues and discussed this at some length.
I think Cylinder 1 can also be vulnerable.
I reckon that's caused by two or more factors, as @gregt identified, the lack of a good chamfer on the crank itself, potentially the restrictors coming loose, the oil gallery changing size [smaller] in the feed to the crank AND the oil pressure release valve coming in at very close to the peak oil pressure at high revs.
I seem to recall discussing the viscosity of the oil being used coming into the equation as well... Pressure is resistance to flow, if the oil in use is thicker or thinner than the specified one to use then it it will affect both flow and pressure, potentially causing problems. So use the correct viscosity for the temperature range.
On an FZR I have never personally seen wear caused by using too thin an oil... just mostly from neglecting to use any oil at all until the stuff that's in there is a black watery mess full of carbon and acidic combustion by-products.
So I would say run the highest quality lowest viscosity you can get away with. Given that the machine we are dealing with is not an air-cooled underpowered lump hampered by a frame weighing 500kg, 20w50 would not be appropriate.
I'd probably go with a 10w40 or a 15w40 like the Delo 400 that everyone raved about.
I did all my valve clearances not long ago in terms of kms. However it was mentioned that the shims may be quite thin that I was putting in? the clearances were quite varied from memory. The bike has seen a couple of big track days which were awesome.
While shoving my nose in and diagnosing it I did notice blowby coming passed the bloody cam cover bolts, so I think at a minimum the engine needs pulling and a good going over, probably a set of rings.
does any one have a link to the engine critical measurements? big end, main etc.
Thanks Linkin, I believe I was using 10w 40 Motul but I will check when I get home.
Oils Ain't Oils
Read some test articles on motorcycle oils, the more the merrier. Here's two
I will use Amsoil in my project bikes, if I live long enough to see them run. As @Linkin said, change the damn stuff. Most of the engine rebuilds I had to do in my life were also of the filthy black sludge variety.
Speaking of shells
Wouldn't it be great if we could get these for the 250 fours. I asked them what their MOQ is for custom sizes just for shits and giggles.
I had one with a rattly top end - whacked in a Chinese chain (with trepidation, as it had 1 less link laterally). Same. I had split the cases to also check channels into main bearings (OK), but pulling maggy is none too easy.
1. Remove the tensioner (centre bolt 1st) to see how far in the plunger is. Chains are ratsh before the limit btw.
2. If it smokes at startup, stem seals - but really, really fiddly. $6 for the set, bewdy, but years off your life.
3. Compression test. Then you know ya got no choice but to swap pistons (piss easy) etc. Gauge with extension hose is $28, else leakdown: hit it with >130psi and feel what's happening at the breather.
In the resources section you'll find:
The 2KR service manual in Japanese
The 3LN1 supplement - for specs the useful portions commence in section 2 - the second column on page labelled 2-1 and the first column on 2-2 primarily
@gregt has said that for racing [track days would be included] the bearing clearances as shipped were too tight - he aims for 0.0016" [which is 0.040mm] for mains journals and 0.0018" [which is 0.044mm] for big end journals - OEM 3LN specs are 0.023-0.047mm for both
Piston to bore clearance is 0.04-0.06mm - pistons measured on the skirt, 5mm up from the bottom
Cylinder out of round and taper limit 0.03mm
Most of the other specs/measurement make sense from the context on those two pages.
The 3LN6/7 specs sheet in English - very useful
Zeal 250 spec sheet in English - very useful