racer4
L plate rider.
Posts: 19
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Post by racer4 on Apr 11, 2020 9:52:17 GMT 1
Other than sending the oil pump off to Arrow and using genuine Yamaha oil seals, what else is a must do when refreshing a 250 LC engine ?
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Post by copper99 on Apr 11, 2020 10:17:37 GMT 1
Bush the crankcase where the gear shaft exits the case, elminate any risk of a small but annoying oil leak ...check the shaft itself isnt pitted or worn out as well.
That was my No1 annoyance after having my engine rebuilt first time around.
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Post by chrisg on Apr 11, 2020 10:17:38 GMT 1
Other than sending the oil pump off to Arrow and using genuine Yamaha oil seals, what else is a must do when refreshing a 250 LC engine ? Probably depends on the mileage and what you are going to use it for. If you are going to use it a lot, maybe new crank and re-bore, if they are approaching their "end of life" dimensions. |
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racer4
L plate rider.
Posts: 19
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Post by racer4 on Apr 11, 2020 10:27:29 GMT 1
Thanks .. this is the type of advice needed
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Post by midlifecrisisrd on Apr 11, 2020 10:37:20 GMT 1
Genuine head gasket
Genuine crank and sprocket seals as a minimum(rest can be changed without splitting)
Gear change shaft and bush mod
Crank refresh while it's in bits
Bottom end will last forever after that
Steve
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Post by russie on Apr 11, 2020 12:31:30 GMT 1
Closely inspect the gear teeth, selector forks and their corresponding grooves in the respective gears. If you do nothing else to the crank then you might as well change the outer main bearings at the very least. Carefully check the adjustment of the pin that the gear change shaft spring locates on (it’s eccentric and adjustable), it could be affected by bushing the shaft. Check if the primary drive gear and clutch basket gear backlash numbers are compatible. Replace the piston rings even if you’re not changing pistons or doing a rebore and make sure the end gaps are not less than 0.3mm. One thing I probably can’t stress enough about what you’re doing is cleanliness, I know it’s stating the obvious but a small amount of foreign object debris in the wrong place can undo all your good work and defeat the purpose of doing it in the first place. Take your time, stop if you need to and most importantly, enjoy it!
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Post by muttsnuts on Apr 11, 2020 13:02:40 GMT 1
check and replace the idler gear and also the kick starter gear if they are wobbling badly, also check the clutch basket for grooving and wear also the inner clutch hub for the same. Gearbox bearings for play, and also if they are notchy when spun etc, exhaust studs for corrosion and signs of strecthing/over tightening, replace while the barrels are off, its way easier, also barrel studs, check for same, head for flatness, barrels for flatness, deck height of pistons and if bore is 1.50mm or over, then be sure to check the head gasket and piston clearance as they normally touch and require the head gasket trimming.
Clean out all crankcase threads before re-assembly as you can easily snap the 6mm bolts if the holes are full of old sealant etc, use a 6mm tap to clean them all out, its worth the effort, again, run an 8mm die downt he crank case stud threads, or at least wire brush them to be as clean as possible
Clean/dry all sealant surfaces, especially the 2 crank case halves with brake cleaner or neat alcohol and wipe dry with a lint free cloth
if re-using the original pistons etc, fit new rings and gap them, also new circlips and little ends
HTH
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Post by 4l04ever on Apr 11, 2020 13:38:08 GMT 1
As mentioned by mutts, the idler gear needs attention. If the gear is fine, I provide a service to fit a new bush.
The gear selector star and stopper arm can be upgraded while you have access.
The gearbox bearings all need checking for play and for smoothness.
Use Yamahbond or Threebond 1215 to seal the crank case halves, not silicone sealant. Also use the Yamabond to seal the inlet gaskets and reed blocks as they are a common place to have an air leak.
Once the engine is fully reassembled, you should perform a leak down test to make sure you have no air leaks.
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Post by dusty350 on Apr 11, 2020 19:55:32 GMT 1
I always like to start with vapour blasted cases. Not a "must do" job, but it never feels right to me to build up the engine in grotty cases ! It helps identify any areas of damage too. Otherwise, everything the guys have said. I always use genuine Yamaha wherever possible - there is a lot of parts still available new for the Lc and Pv engines so that's good for us. Take lots of pics of the strip down - it will help you on the rebuild. I take each component in turn and pop it in a freezer type re sealable bag when stripping down. You can then take a bag at a time and clean/inspect the contents, and renew as necessary. Make yourself a cheap engine stand out of offcuts of wood - really makes life a lot easier when rebuilding the bottom end. Dusty  |
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Post by bare on Apr 11, 2020 20:15:49 GMT 1
Genuine head gasket Crank refresh while it's in bits Bottom end will last forever after that Steve Welll.. crank could last 20,000 kms or 2,000. Too many factors involved. |
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Post by midlifecrisisrd on Apr 11, 2020 21:25:06 GMT 1
Genuine head gasket Crank refresh while it's in bits Bottom end will last forever after that Steve Welll.. crank could last 20,000 kms or 2,000. Too many factors involved. I did mean relatively speaking Its a 2 stroke, it will sh1t itself at some point 🤣 Just good to know what point it started at and not gamble on pins not being pitted from lying Steve |
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Post by veg on Apr 12, 2020 6:25:13 GMT 1
See mr happy has visited.
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Post by 4l04ever on Apr 12, 2020 13:17:13 GMT 1
Also check that you have a matching pair of engine casings. There are hand engraved numbers behind where the stator plate is fitted. The number on the top casing should match the number on the bottom casing.   |
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Post by 4l04ever on Apr 12, 2020 13:18:38 GMT 1
Also check numbers on primary drive gears. Crank one is usually round 80 to 90 range and the gear on the clutch is around 60 to 70. The two numbers added together should be either 154, 155, or 156.
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Post by Gunny on Apr 12, 2020 15:06:14 GMT 1
What happens if you use a mismatched pair ? (serious question)
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Post by arrow on Apr 12, 2020 15:25:58 GMT 1
What happens if you use a mismatched pair ? (serious question) If the fit is too close they will run tight when the engine is hot and shorten the life of the bearings and the gears. Too loose and they are noisy and the gears wear out quicker. |
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Post by jon on Apr 12, 2020 15:47:56 GMT 1
What happens if you use a mismatched pair ? (serious question) If the fit is too close they will run tight when the engine is hot and shorten the life of the bearings and the gears. Too loose and they are noisy and the gears wear out quicker. I had an LC with bottom chain damage, and another good (non matching lower case). They looked to be OK, but I still opted to cut out the missing piece from the good lower case and have it welded to the chain damaeged but matching case, Fact is it’s a lottery. Some work, some don’t. I’d much rather have a repaired case than non matching. Jon |
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Post by 4l04ever on Apr 12, 2020 16:38:15 GMT 1
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