Help FZR250r 3LN1 Project

You've got some time available, what about going though and checking what clearances you need with the 158 - 160 shims, I think that may be insufficient to get a read on a few valves - then machine down one or two of the 160's to say a 155 and a 150 to get some measurements on the others with 0 clearance.

And now that I've typed all of that, you've obviously got skills and the necessary tools, what about cutting some shims yourself from the back end of a 7.5mm or a 19/64 drill bit, or machine down the O.D. of a piece off of the back of a drill, trimmed down to 7.48mm could be used to go into the chuck jaws to seat the current shims against and hold them square for machining

 

There is a way out even in lockdown.Back in the day, at the first WSB round in NZ, a local had an OW01 with the soft kit valves. He lost clearance every time he took it out - as those valves were known to do.
The pit counters were thick baulks of dressed timber. I watched them place a shim on the bench, then hammer it level with the surface. Then pull out a disc grinder and attack the shim....Then check with a micrometer.
After the meeting, they pulled the top off the bench and turned it over - clean wood.

I must confess that a couple of times over the years I've done this myself.

If you want to make shims - again, I've done this. Use silver steel round bar. It's soft and can be machined and filed/ground to thickness. Once you've got what you need, it's heat to cherry red and drop into some old oil. This hardens them nicely.

 

AH, that makes sense, they have the darkened colour of a heat treatment and now that I think about it, every time you see valve tips and faces being machined it's with grinding wheels obviously to deal with the hardened tips and stellite faces, so sensible that the shims should be appropriately hardened also

Gregt just beat me to it - what about a dremel with a drum sanding attachment and the shim installed into the lathe at a slow rotation - that will ensure that they are even at the circumference, then face them gently on some 400-800 wet and dry on a sheet of glass

You could try a thin cutoff disc in a 5" or smaller grinder/polisher with a speed control and the shim spinning in the lathe, don't know if I'd attack one with a 10K RPM grinder and expect any control though

Makes the bought ones seem like such good value when you consider the work needed to make them yourself

 

OK, so we've had a few play up recently and not start after having cams out for one reason or another

You've already tagged the cams in the incorrect positions, then there was someone else that had just done the valve clearances, replace everything with crank aligned to the incorrect mark on the flywheel - there are multiples marks of the flywheel, I think @Linkin spotted that error - that one wouldn't spin through by hand, it encountered resistance

https://www.2fiftycc.com/index.php?threads/fzr250-project.10828/page-5#post-131645

Final suggestion is to check that each coil is driving the correct plugs - plugs 1 & 4 on one coil with plugs 2 & 3 on the other

This thread has the plug swapping on the coils as well as coils connected incorrectly whilst we were in the process of discovering that the cams were in the wrong spots

https://www.2fiftycc.com/index.php?threads/first-bike-the-fzr250-3ln.10816/page-2

https://www.2fiftycc.com/index.php?threads/first-bike-the-fzr250-3ln.10816/page-5

hope this helps

 

That's the domain of either threebdond engine conditioner if you can locate some

Threebond is recommended by Subaru for unsticking rings and removing built up engine gunk

or otherwise you can mix up the equivalent of seafoam, which I posted the formula for here

https://www.2fiftycc.com/index.php?...-fzr-250-some-advice.10855/page-2#post-130958

There's a formula for something called seafoam which is either kerosene or diesel @ about 60% plus isopropyl alcohol @ 15% and shellite @ about the final 25%

You can put small amounts down the plug hole, ideally the cylinders would be vertical,so engine out and propped up, but it's worth a try for a few days at least

 

Pop the pistons off of the rods and clean the ring lands till they are spotless, if it's really gunked on in the ring lands, then I've used oven cleaner successfully, beware fumes, spray it on, then wait max 60 seconds, toothbrush to remove, otherwise gentler things like diesel, kerosene and shellite are great.

Are they new rings?

The ring land clearance should be in the manual, I don't know it off by heart, it's tiny, but they shouldn't jam in there.

2000 grit on glass should work to level them

OK, I just spotted something, they look to be 2KR pistons because of the full round skirt at the bottom, the 3ln1 pistons are slipper pistons

2KR pistons don't go onto 3LN rods because they lengthened the rods by 2mm: 80mm 2KR -> 82mm 3LN

They would hit the cylinder head because of the different compression height

Compare - 2KR pistons
https://www.aliexpress.com/item/32996977971.html



3LN1 pistons
https://www.aliexpress.com/item/32276337915.html

 

Ok, then it's likely a 2KR motor, I don't think anything beside rod length and pistons changed between them.
Stroke remained unchanged all through @34.5mm

We can cross reference parts lists to check the cylinder head, but I've got a zeal cylinder head which is the same part I.D. as my 3LN1.

I do know that 2KR, 3LN1 -> 3LN5 had the same power output, 3LN6/7 and zeal had lower output attributable to perhaps all of or some of cam(Zeal for sure), valve sizes, carbs 28mm I.D. -> 26.5mm I.D. and ignition boxes and timing.

One thing to know if it's a 2KR head is that the valve stems are ~4mm, whereas later models used ~3.5mm, valve sizes did change somewhere through the series, I think they may have increased from 2KR -> 3LN1-5, then decreased, I definitely know for the zeal, unsure if they decreased for 3LN6/7 to reduce power output.

 

While you've got the head removed, just for interest sake, measure the valve head diameter and stem diameter to know if it's 2KR or 3LN for certain.

And as I mentioned I've got a Zeal cylinder head, same casting I.D. as 3LN1, although I get the impression that the Zeal could have been assembled out of bits to hand at the time, and I'd need to measure the valves on the Zeal head again to be certain of this detail, however IIRC - they weren't what's in the zeal specs but 3LN1/3/5 specs

 

Wondering if they are already new rings to be as ill fitting on the pistons as they are, IIRC, you did measurements on your new Chinese rings for the FZR400 and they came in in spec

Forgot to mention, the reason for thinking that they are perhaps Chinese rings already is because that's paper cylinder base gasket in the photo with the pistons

found it

https://www.2fiftycc.com/index.php?threads/chinese-rings.7840/

Looks like a full set of measurements of the rings he has might be appropriate