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Post by donkeychomp on Aug 2, 2023 22:41:33 GMT 1
Ohhh shit...
Alex
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Post by JonW on Aug 3, 2023 0:25:25 GMT 1
Wow! Its like it became a two stroke.
"A valve in the hand is worth two in the motor" or something...
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Post by Tobyjugs on Aug 3, 2023 10:12:52 GMT 1
Bugger What a pity, you were so close. I bet you still still have fond memories. As for root cause I would say the following; Middle age man (almost 18) thrashing the shit out of a tiny engine.
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Post by steve63 on Aug 3, 2023 10:29:39 GMT 1
Bugger What a pity, you were so close. I bet you still still have fond memories. As for root cause I would say the following; Middle age man (almost 18) thrashing the shit out of a tiny engine. No, honestly, I rode with more mechanical sympathy than ever before. One of the guys asked the day before why I had dropped back so much at one point. It was because I was holding back on the down hill bits and not letting it over rev. The guy on the Jin Lun went past me on one of the downhill bits and said he saw 70 on the clock and 1,500 into the red. I thought I'm not blowing this up just to see what it would do. The plan was that once we reached John O Groats I would unleash the beast and see what it could do! It was purring along at 50 quite happily and bang! There's that niggling feeling of failure eating away. There's a small glimmer of sorting the carnage out and finishing the job. It might be the only way to ease the pain of failure 😁
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Post by Tobyjugs on Aug 3, 2023 11:36:44 GMT 1
Just from the pictures i've seen my first prdiction would be the valve failed.
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Post by steve63 on Aug 3, 2023 12:52:52 GMT 1
Just from the pictures i've seen my first prdiction would be the valve failed. Seems that way to me. Just odd it would do it 1,210 miles into the trip. 1,400 since I've been riding it. Here's an oddity. Taking the alternator cover off there was an M6 washer stuck inside the rotor. Also there was what looks like a piece of welding wire maybe 20mm long and 0.5mm thick stuck to the stator. I say welding wire because it has a molten blob at the end like the end of your MIG wire. The crank is smooth as silk and I would be tempted to give it a swish out but I think I'll give it a complete strip. I can see a piece of piston down there next to the crank 😆. Made myself an engine stand. I have two engines to strip and it was pi$$ing me off chasing it around the bench 😁. This is why you always pick up any bits of interesting metal out of the scrap bin. This engine seems to have a much different charging and ignition system to the other one with different connector blocks. At the moment it looks like my bottom end with the other engines top end is the way to go.
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Post by steve63 on Aug 3, 2023 16:12:19 GMT 1
That was a stroke of luck. A clutch holding tool I made for my RD200 years ago fits the SR125. Saved.me a lot of time. Things I've learned: having an engine stand is brilliant. I will be making one for the LC's. Maybe one that I can turn the engine over in. The £3.50 I paid for an impact driver in around 1980 was the best £3.50 I ever spent. This job would have been impossible without that and the extended and standard JIS bits I bought a few years ago. One crankcase screw actually sheared. That takes some doing without mashing the screw head up.
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Post by 4l04ever on Aug 5, 2023 17:52:25 GMT 1
Hybrid time??? What could fit in there? :-)
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Post by 4l04ever on Aug 5, 2023 17:53:04 GMT 1
SDR200 Engine???
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Post by Tobyjugs on Aug 5, 2023 18:32:57 GMT 1
Hi Steve what is that piece of twisted wire in the plastic lid?
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Post by JonW on Aug 6, 2023 0:35:21 GMT 1
RD/DT125/200 engine might go in these?
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Post by steve63 on Aug 6, 2023 8:17:34 GMT 1
Hi Steve what is that piece of twisted wire in the plastic lid? I'm just looking at that photo now and it looks like it. There was only a piece of what looked like stainless wire about 0.5/0.7mm and about 20mm long that I found near the alternator. It has a molten end like you see on the end of your MIG wire.
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Post by steve63 on Aug 6, 2023 8:26:08 GMT 1
RD/DT125/200 engine might go in these? There may be options but anything else would be quite expensive. I have the spare SR125 engine I only paid £50 for so the plan is to mix and match to make a good one whilst spending as little as possible. I have no idea what condition the top end is on that one until I strip it. Mine had worn cam lobes with a bit of pitting on one and one of the rockers was worn. Hopefully the spare will be better. I've a feeling that any second hand ones will have similar wear unless they have been changing the oil regularly and keeping a close eye on the level. Not much chance of that with these kind of bikes but fingers crossed. The bearing on the output shaft is a bit notchy even after cleaning thoroughly. Coincidentally it's the same as one of the LC wheel bearings, 6304, but a C3 rating. Should only be about £5/£6.
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Post by 4l04ever on Aug 6, 2023 13:06:18 GMT 1
Check OEM specs, but gearbox bearings are normally not C3 clearance asthey don't spin that fast and they don't get super hot.
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Post by steve63 on Aug 6, 2023 13:54:27 GMT 1
Check OEM specs, but gearbox bearings are normally not C3 clearance asthey don't spin that fast and they don't get super hot. There is a 3 at the end of the code but the 'C' is very small but does look like a C. no one has had the engine apart so whatever is in it is what Yamaha put in. I'll have a look at all the others in there.
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Post by steve63 on Aug 6, 2023 18:48:44 GMT 1
One of the crank main bearings, the one that stayed in the case, is a C4. The other is on the crank and is in a bag in the box somewhere. Oddly another gearbox bearing is 6304 but with no temperature code on it. I wonder if just the output bearing is C3 because it does the most work being on the front sprocket?
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Post by steve63 on Aug 6, 2023 18:51:33 GMT 1
Hi Steve what is that piece of twisted wire in the plastic lid? I've just had a look and it's just that piece of 0.7mm wire. It's the resolution of the photo that makes it look twisted. All I can think is that and the washer went it at some point when someone had the two screw in inspection windows off. They're used to set the engine for tappet adjustment. It wasn't me by the way 😆
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Post by donkeychomp on Aug 6, 2023 22:14:12 GMT 1
Steve, what's the plans for the bike when you do get the lump rebuilt?
Alex
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Post by JonW on Aug 7, 2023 0:24:33 GMT 1
Hi Steve what is that piece of twisted wire in the plastic lid? I've just had a look and it's just that piece of 0.7mm wire. It's the resolution of the photo that makes it look twisted. All I can think is that and the washer went it at some point when someone had the two screw in inspection windows off. They're used to set the engine for tappet adjustment. It wasn't me by the way 😆 Some 6 year old was pissed off with his dad or older brother and when his back was turned during some routine maintenance he dropped what he'd been playing with from the garage floor into the hole in the side of the engine... hes 30 now and has kids of his own... karma will get 'im!
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Post by urbantangleweed on Aug 7, 2023 7:17:56 GMT 1
Great effort on the challenge and that SR needs a good kick in the nuts for letting go so near to the end.
What about rebuilding it and riding it to the campsite you stayed at on the night before that fateful day and then do the stint to JoG? That way you completed the journey, doesn't really matter that it wasn't all done on the same trip?
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Post by steve63 on Aug 7, 2023 7:20:59 GMT 1
Steve, what's the plans for the bike when you do get the lump rebuilt? Alex I don't honestly know. Part of me wants to go back up to Edinburgh and finish the trip. Part of me wants to just sell it. I would like to finish the trip either way even if it's on the Honda. I missed out on the part I was looking forward to the most which was the part north of Edinburgh. Our plan initially was to use more B roads for the whole trip but the rain and the limited time (one of the guys starts a new job today, the others Wife had a race on Saturday in the MG) meant we chose a faster route. We did use some B roads on the ride back from Lands End to the first campsite. They took us down some fantastic roads along the north coast of Cornwall. A few people have said that if I'm riding to the north of Scotland then I should go up the west coast. My Mrs actually asked if she could have it and learn to ride on it. I'll just finish the job and think about it again when it's done.
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Post by steve63 on Aug 7, 2023 7:24:41 GMT 1
Great effort on the challenge and that SR needs a good kick in the nuts for letting go so near to the end. What about rebuilding it and riding it to the campsite you stayed at on the night before that fateful day and then do the stint to JoG? That way you completed the journey, doesn't really matter that it wasn't all done on the same trip? Yeah that's my thinking. To be fair it's the best I can do now. I was saying everyday to the others that it sounded louder and they kept answering that I say that every day 😁. I have some on board video and it does sound a bit clattery but it always did. Other than over revving I don't know what would cause a valve to fail so I can't think that there was anything that could have prevented it. Seems I might have been right about the noise. It's going to be lack of holidays that stop me finishing it this year now unless I do a Friday/Saturday/Sunday ride.
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Post by urbantangleweed on Aug 7, 2023 7:43:01 GMT 1
Perhaps with always being a bit clattery the piston had been just kissing the valve due to incorrect clearance and/or slight play in the little or big end all that time and eventually it fatigued the valve?
Must be a few good weekends due before Winter sets in to allow you to complete the task in the same year you started it, maybe even in decent weather, you could perhaps be standing smugly in the sunshine at JoG while raising a middle finger to the SR?
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Post by steve63 on Aug 7, 2023 10:23:52 GMT 1
Perhaps with always being a bit clattery the piston had been just kissing the valve due to incorrect clearance and/or slight play in the little or big end all that time and eventually it fatigued the valve? Must be a few good weekends due before Winter sets in to allow you to complete the task in the same year you started it, maybe even in decent weather, you could perhaps be standing smugly in the sunshine at JoG while raising a middle finger to the SR? It was a bit clattery but the cam, especially the exhaust side, is worn past the service limit and the rocker is as well. That would account for the excessive tappet clearances, double on the exhaust side and still quite a bit over on the inlet side. I put the tappets right. My logic is that the wear on the cam and rocker would decrease valve lift and hamper "performance" 😆 but that should have increased clearance between valve and piston? We need a 4 pop expert to give us their opinion. I've rebuilt a 400four and a couple of Honda 70's so I know what goes on. My 4/4 had four bent valves and a knackered piston but then again it had snapped a cam chain so it's to be expected. Before anyone jumps on it, it was like that when I bought it, not guilty! 😁. BTY the crank feels silky smooth, no play anywhere. A few marks on the top of the con-rod now though. I don't think it even has a small end. The gudgeon pin just runs in the con-rod small end eye.
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Post by midlifecrisisrd on Aug 7, 2023 12:38:20 GMT 1
Not an expert in any way on 4 strokes but if the cam lobe is worn it will affect the smoothness of the valve opening and closing so will stress the valve more at its weakest point
Think it's also normal to have no bearing in the small end of the conrod
Steve
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Post by Tobyjugs on Aug 7, 2023 21:21:30 GMT 1
It's sometimes difficult to find the root cause of such a failure without getting your hands on it.
I would be checking to see if the valve had difficulties closing due to sticking in the valve guide. Excessive wear in the guide can lead to the valve not seating correctly causing stress in the valve stem and disc. Check the collects are still in place. I guess if the spring failed that would be easy to see. Try to look for any burning on the outer edge of the valve disc. Burning will tell you it was not closing properly. As mentioned by Urban check to see if it was possible for piston to hit the valve. Generally it's better to hear the ticky noise of valve clearances then not to hear it. Except for in high revving engines. A couple of years ago I rebuilt an R6 engine for someone and I set the valve clearances on the larger side of the given tolerance. I was given the advice to set them to smaller side of the tolerance which I did.
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Post by urbantangleweed on Aug 8, 2023 6:59:43 GMT 1
Perhaps with always being a bit clattery the piston had been just kissing the valve due to incorrect clearance and/or slight play in the little or big end all that time and eventually it fatigued the valve? Must be a few good weekends due before Winter sets in to allow you to complete the task in the same year you started it, maybe even in decent weather, you could perhaps be standing smugly in the sunshine at JoG while raising a middle finger to the SR? It was a bit clattery but the cam, especially the exhaust side, is worn past the service limit and the rocker is as well. That would account for the excessive tappet clearances, double on the exhaust side and still quite a bit over on the inlet side. I put the tappets right. My logic is that the wear on the cam and rocker would decrease valve lift and hamper "performance" 😆 but that should have increased clearance between valve and piston? We need a 4 pop expert to give us their opinion. I've rebuilt a 400four and a couple of Honda 70's so I know what goes on. My 4/4 had four bent valves and a knackered piston but then again it had snapped a cam chain so it's to be expected. Before anyone jumps on it, it was like that when I bought it, not guilty! 😁. BTY the crank feels silky smooth, no play anywhere. A few marks on the top of the con-rod now though. I don't think it even has a small end. The gudgeon pin just runs in the con-rod small end eye. Yep, I'd have gone exactly the same way as you did and figured that slightly loose was better than slightly tight.
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Post by steve63 on Aug 8, 2023 12:49:41 GMT 1
It's sometimes difficult to find the root cause of such a failure without getting your hands on it. I would be checking to see if the valve had difficulties closing due to sticking in the valve guide. Excessive wear in the guide can lead to the valve not seating correctly causing stress in the valve stem and disc. Check the collects are still in place. I guess if the spring failed that would be easy to see. Try to look for any burning on the outer edge of the valve disc. Burning will tell you it was not closing properly. As mentioned by Urban check to see if it was possible for piston to hit the valve. Generally it's better to hear the ticky noise of valve clearances then not to hear it. Except for in high revving engines. A couple of years ago I rebuilt an R6 engine for someone and I set the valve clearances on the larger side of the given tolerance. I was given the advice to set them to smaller side of the tolerance which I did. Everything is so badly damaged now it's doubtful any conclusions can be drawn from the corpse. It's like one of those cases where the body is so badly decomposed that a cause of death cannot be reliably found
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Post by steve63 on Aug 8, 2023 22:39:07 GMT 1
The spare engine on the engine stand. A cylinder head looking like it's supposed to look. Yamaha have changed the charging and ignition systems from left, my original, to right, the spare engine. It means that even though this engine looks in great condition internally I can't just swap them. Hopefully the top ends are a straight swap.
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Post by JonW on Aug 9, 2023 1:55:05 GMT 1
Will the two different stator/rotors/cover not fit the same crank & cases and just allow a swap?
I ask that as the cases look to have the same fittings spacing etc.
I'd be a bit worried about reusing the crank from the blown motor when the other one looks so good and be trying to swap the stator/rotor and poss the cases over to use as much of the better engine etc
Also... can you not just swap wires to make the different one work? Im going to say the left one looks 'earlier' as its more like my XT500, ie 70s, the right one looks like an LC/YPVS etc so 80s.
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