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Old May 31st, 2023, 03:42 PM   #1
Sploomph
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Question Lots of questions - new to forums and riding

Newbie to the forums and riding here,
I tried using the search but couldn't find anything on these specific questions so if anyone could link a post or copy and paste i'd really appreciate it!
What's the difference between the 86-07 250's and the 08-12 250'? What would I have to do to put a 08-12 250 into a 86-07?

What would I have to do to put a 300 into a 250 frame?

Reason I ask is im having compression issues with a junker I got for cheap and i'm considering saving myself some time and energy by just swapping in a working engine.
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Old May 31st, 2023, 04:12 PM   #2
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Welcome to the board, John. I know you can put a newgen 250 engine in a pregen chassis. There are a few details needed that I don't have experience with, but others here do. I kinda like the pregen engines better, so I'd probably try to find a used good one cheap.
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Old June 1st, 2023, 12:32 AM   #3
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'86-87 1st-gen is completely different than '88-07 pre-gen or '08-12 new-gen.

If you swap engine to any other generation, you'll also need these parts that goes with engine:

- matching upper engine-mounts, also supports different radiator for each generation
- matching engine-harness and sensors
- matching ignitor box, '86-87 uses different analogue ignition system
- matching carbs, each of these 3 generations uses different carbs
- matching exhaust system
- matching dash, tach won't work

Same with 300, need entire EFI system too. Otherwise, you'll be spending A LOT of time dyno-tuning 300 engine with carbs that were never designed for it.
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Old June 1st, 2023, 12:42 AM   #4
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Which year bike do you have?

'86-87 1st-gen


'88-07 pre-gen ('88-94 has different cams & wiring-harness than '95-07)


'08-12 new-gen
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Old June 1st, 2023, 05:38 PM   #5
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Which year bike do you have?
Sorry for the late response but its a 2007!
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Old June 1st, 2023, 11:09 PM   #6
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Hmm, I do happen to have:

- spare '08 engine
- upper engine-mount & radiator bracket
- new-gen radiator
- matching Area-P exhaust
- new-gen carbs with factory jetting for '08 engine

lemme see if there's anything else that's needed for swap...

So related engine-swap threads;

https://www.ninjette.org/forums/showthread.php?t=386858
https://www.ninjette.org/forums/showthread.php?t=191906
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Old June 2nd, 2023, 06:23 AM   #7
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Thanks Danno for the reply. I might end up buying if the price is decent but ill see if these rings and headgasket will fix compression first.
On a seperate note, anyone know the torque sequence for the head? I would assume criss-cross from outside inward since theres nothing anywhere about it.
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Old June 2nd, 2023, 10:29 AM   #8
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Welcome to the board, and to riding!
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Old June 2nd, 2023, 12:45 PM   #9
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Quote:
Originally Posted by Sploomph View Post
Thanks Danno for the reply. I might end up buying if the price is decent but ill see if these rings and headgasket will fix compression first.
On a seperate note, anyone know the torque sequence for the head? I would assume criss-cross from outside inward since theres nothing anywhere about it.
Inside out makes more sense. Like big sticker, you don't want stuff bunching up in middle.

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Old June 4th, 2023, 11:07 AM   #10
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Alright after fresh rings, head gasket, and a minor hone i'm still having compression issues. I'm getting 90 dry and 130 wet on Cylinder 1 and 60 dry and 90 wet on Cylinder 2.

I'm pretty sure its the cylinder though as there was some weird very hard gunk built-up on the cylinders, carbon maybe? Cylinder 1 had very little of it, just a smudge-like trail. Cylinder 2 was much worse having an outline of the piston skirt of gunk. I honed the crap out of it and it didn't do much at all. I took it to a machine shop down the road and they said to run it and see what happens but that they'd "seen worse work".

So, at this point i'm trying to figure out where to go from here. If these things can be re-sleeved I'd rather do that, but I've never heard of anyone doing that. I have heard of people getting oversized pistons but looking online they are a little bit expensive. New cylinders can be found online too but most aren't really in any better condition.

Idk, what do you all think?
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Old June 4th, 2023, 12:16 PM   #11
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That would seem to indicate that the valves are not sealing well. Have you checked the valve clearances? These engines tighten up the clearances with use, and it's worse when the engine is cold, so it's not unusual for the valves not to seal when cold.
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Old June 4th, 2023, 12:21 PM   #12
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That would seem to indicate that the valves are not sealing well. Have you checked the valve clearances? These engines tighten up the clearances with use, and it's worse when the engine is cold, so it's not unusual for the valves not to seal when cold.
Nah I made sure timing and valve lash was perfect. But would that explain the difference in compression between cylinders? I checked the head and cylinder with a straight edge and feeler gauge too - it was good. Filled the combustion chamber with water and sprayed 60+ psi of air into the inlets - no bubbles. Head Gasket is brand new and hasn't gone through any heat cycles and mating surfaces are clean.

Any other diagnostics I could do?
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Old June 4th, 2023, 02:29 PM   #13
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Well, something is leaking. Even with oil added, you're getting low numbers. If it's not the valves leaking, it has to be something else like a leaking gasket or a crack somewhere.
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Old June 4th, 2023, 04:50 PM   #14
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Did you measure piston to cylinder clearance before & after honing?
Did you cross-hatch cylinders for new rings?
Did you measure ring end-gaps?
Measure valve-seat contact width?

Depending upon what those numbers are, that's difference between worn-out engine vs. new.

For new rings, you don't need any honing. That's only for removing material when fitting new oversized pistons. Basically just follow steps in manual, 1,2,3, etc.

Last futzed with by DannoXYZ; June 4th, 2023 at 05:55 PM.
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Old June 4th, 2023, 06:40 PM   #15
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Quote:
Originally Posted by DannoXYZ View Post
Did you measure piston to cylinder clearance before & after honing?
Did you cross-hatch cylinders for new rings?
Did you measure ring end-gaps?
Measure valve-seat contact width?

Depending upon what those numbers are, that's difference between worn-out engine vs. new.

For new rings, you don't need any honing. That's only for removing material when fitting new oversized pistons. Basically just follow steps in manual, 1,2,3, etc.
No, Yes, Yes, and No.
I dont have the tool to measure clearances and didn't know that was a thing.
I did cross hatch the cylinders pretty well.
The endgaps were within spec.
I didn't measure it as i didn't have the tools and I also didn't know that was a thing. But wouldn't the water test make sure the valves are sealing good?

And I know you don't have to hone for new rings but I was worried about some weird gunk on the cylinder. The gunk is hard enough that my nail would catch on it. After honing it for a bit, the gunk on Cylinder 1 was still visible but gunk on Cylinder 2 was still there. I took it to a machine shop down the road and they said they'd "seen worse".
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Old June 5th, 2023, 04:50 PM   #16
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Engine-building isn't so much about swapping parts as it is about getting numbers right, which is 99% of effort. Trick is "blueprinting" steps, picking numbers that's most optimal given available production tolerances.

1. To remove deposits (burnt carbon from using non-synthetic oil), you'll want to use some kind of chemical that doesn't affect metal cylinders, such as B12/PB-blaster with 3M green scotch-brite pad. Cylinder-clearances should be at minimal end of range at top. I prefer taper-bore with mid-range clearances at bottom to relax stress on rings. Right now, most likely you've got too-large clearances between piston & bore. Leading to excessive piston-rocking with prevents rings from sealing. You can get replacement cylinders here (no boring, just minimum plateau-honing with brush/ball flex-hone to create cross-hatch, 5-10s max, angle between 28-35 degrees): https://www.ronayers.com/oemparts/a/...inder-piston-s


2. What gaps did you measure? Ring-end gaps is primary difference between worn vs. new engine. Buying pre-gapped rings just gives you pre-worn engine. I find tigher-then-spec works best for power and longevity. I'll install multiple sets of rings to find optimum setting. Start 1st set at tight end of factory spec. Then pull engine out after couple hundred miles and install tighter set and repeat. After 4-5 sets, I may see fretting-marks at end of rings, that set is too tight and I'll re-install previous set, done! Typically ends up being about 1/2-3/4 of minimum amount specified in manual.



4. Valve-seat sealing is all about pressure. Valve-springs provide fixed amount of clamping-force. As seats wear, their contact-width increases and you have less pressure per unit area (PSI). Mistake most people make is lapping their valves when rebuilding. They are "pre-wearing" their valve-seats by increasing width of contact and lowering clamping-pressure per unit area. This is most likely where you're losing 67-75% of your sealing. Every single Ninjette engine I've had apart have had worn-out valve-seats with too-large contact ring. Worse on pre-gens due to less-durable valve-train and more years of abuse. This engine has contact-width of 2,5mm on intake and 3,0mm on exhaust, way, way worn!!!



Specs from manual is 0,5-1,0mm contact seat width. Lapping does not improve sealing because it spreads out spring-force, leading to less pressure!



Proper procedure is to grind 32 and 67,5-degree upper & lower cuts to reduce 45-degree seat-area back to 0,5mm width. Then you've increased clamping-pressure from same valve-springs and seal is much, much better.



Water's not good for testing because it has surface-tension (it pulls itself together). Alcohol's typically used to test, but even then, it's not accurate model of actual combustion-pressures. Best to use vacuum or pressurised air since it has lowest viscosity. On high +12:1 engines, you'll see combustion pressures in 1000-1500psi range, depending upon RPM & load.





Not easy to model and test that on bench. Best to follow manual and cut valve-seats to minimum width. Old grinding-stones method is not longer needed. Modern Sunnen/Serdi machines can do all 3 angles in single pass (along with valve unshrouding):



Link to original page on YouTube.

Link to original page on YouTube.


Last futzed with by DannoXYZ; June 5th, 2023 at 06:02 PM.
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Old June 5th, 2023, 07:04 PM   #17
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Thanks Danno for the boat load of info. I forgot exactly what the specs were on the rings but they were definitely on the looser side. I didn't have to ground down a single one. And earlier when I mentioned the water thing I meant this: https://www.youtube.com/watch?v=krAx...el=DoesItTrack

I'm 99% sure the sleeves were trashed from the start so I figure that will be a good start, right? If that doesn't fix it I'll go from there with the valves.
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Old June 5th, 2023, 09:37 PM   #18
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Yeah, that water-test is useless because you can't put 1000psi in that direction to test. It would creep valves open. It only takes like 10psi to open them.


Start with new cylinders and pistons. Use profilometer to measure:

Rpk - reduced peak height
Rk - core roughness
Rvk - reduced valley depth

properties of surface prep, which greatly affects piston ring seal.

Make sure all measurements are on tight end of clearance range, piston-to-cylinder, ring end gaps. If you're going to be building pre-worn engine, just get used one from junkyard.

Also measure your bearing clearances and get new bearings towards tight end of range. Don't re-use rod-bolts.





And get Cometic all-metal multi-layer headgasket #C8828. Spray 3 layers of copper-coat spray on both sides and let each layer dry fully before next and before installing. Be extremely careful when placing gasket on deck that middle sandwiched layer didn't escape and overlapping outer layers. Gently lower head onto gasket making sure not to disturb gasket.

Last futzed with by DannoXYZ; June 10th, 2023 at 10:00 AM.
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Old June 6th, 2023, 06:00 PM   #19
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Alright, I will let you know how that goes! Will probably be a while though.
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