Author Topic: New bike, terrible rattle/shake at 3500+ RPM  (Read 436 times)

Offline Kylll

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New bike, terrible rattle/shake at 3500+ RPM
« on: November 13, 2019, 01:20:27 AM »
Hi all.

Been stuck with my first project bike for the past 3 months. Bought the bike with a knocking sound at 3500+ rpm and decided to rebuild the entire engine to see if i could fix it.
disassembled and reassembled twice now, same issue. On initial disassembly i found that one of the piston guides (i think that's what they're called? they're extended pieces of the piston that move up/down the cylinder) has been broken. Bought two new pistons, replaced them, replaced conrods too (including new bearings) but the crankshaft stiffended up for 30 degrees of rotation out of 360. Being naive figured this was probably not an issue, reassembled and was struck with a terrible noise coming from the motorcycle at 3500rpm. A violent shaking sound, similar to a phone's vibration. Thought this might be the crankshaft, disassembled everything, found some shrapnel between conrod and crankshaft, sanded it down and it was perfectly smooth.

Same issue after i fired it back up.

Initial thoughts were the crankshaft, don't think that's the issue.
Pretty sure that the counterweight was installed correctly so i doubt that's it.
Camshaft tensioner works fine, camshaft chain measures 158/159 across 20 links (out of spec i believe, will double-check measurements in a sec) but don't think it'd cause THAT big of an issue?
Have quadruple checked the engine timing.

Next step is to remove the motor from the chassis and attempt to run it by itself on some carpet, perhaps a part of the chassis is hitting resonance at 3500? (I doubt this, as the noise simply gets louder as i increase the RPM)

Pretty stuck here. Any help would be appreciated.

Thanks,
Kyle

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #1 on: November 13, 2019, 01:51:11 AM »
'Piston guide' refers to the piston skirt, looked it up. Measurements show 147.5mm across 20 links on the cam chain.

Offline herennow

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #2 on: November 13, 2019, 09:00:45 PM »
wonder if the crankshaft got bent with the piston seizing enough to break the skirt.

when you say "shrapnel between conrod and crankshaft", do you mean a small piece of aluminum . or did the shell bearing seize and get marked?

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #3 on: November 14, 2019, 12:01:10 AM »
Hi, thanks for the reply.

Yes, there was discoloration on the bearing (dark grey with scratch marks) and on the crankshaft too. I replaced the bearing when i replaced the camshaft.
I have attached photo of  the discoloration on crankshaft.

Do you think it likely that the crankshaft has bent? The piston did not seize, the motor was still running when i picked it up, just started making terrible knocking noise (and rattle) at 3500+, now it only makes the rattle.

Have another query on timing. As per service manual i have the '1' mark pointed flush to gasket surface, and 18 links down from '2' mark on exhaust camshaft i have lined up intake camshaft '3' mark, however the marks on the camshafts do not point towards one another and seem to be off by 1 tooth. I have checked the timing is correct (and tensioned) at least 5 times.

Images attached of discoloration and timing.

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #4 on: November 14, 2019, 12:02:56 AM »
Photo of timing mark on exhaust camshaft

Offline Bluesmudge

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #5 on: November 14, 2019, 04:20:43 AM »
This may sound crazy, but have you checked the engine mounting bolts? Especially the one at the front of the frame?
The bike can feel pretty viby if they are loose.

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #6 on: November 14, 2019, 08:15:16 PM »
This may sound crazy, but have you checked the engine mounting bolts? Especially the one at the front of the frame?
The bike can feel pretty viby if they are loose.

Yes. I'm going to run the engine outside the frame when i have it reassembled.
It's not just a slight vibration, the noise coming from the engine is mucu louder than the exhaust (most of baffle has rusted itself apart so it's louder than stock) and the whole bike shakes.

Offline herennow

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #7 on: November 15, 2019, 06:07:58 AM »
wow, that left big end seized badly. I would guess the conrod is bent possibly?

Offline mr72

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #8 on: November 15, 2019, 12:05:07 PM »
Just FYI, I have no direct experience rebuilding an engine-- just being logical trying to read the original post and boil this down:

1. you discovered a broken piston skirt, decided to replace both pistons, both rods and the rod bearings
2. while disassembled, the crankshaft had resistance to 30 degrees of motion *while no rods or pistons are installed*. But you assembled and tried to run it anyway.
3. pulled it apart again, you found metal bits in there, attempted to sand it smooth and reassembled
4. engine now has a loud knock and mechanical shake

Is that about right?

Because if so, I'd say the crank is probably bent, main bearing is scored or spun, which would tear up the bore in the block, etc. One end of the crankshaft is very scorched. If it were me, I would have never reused that part, and I bet there is additional damage to the bore where the crank seats in the block.

While it was apart to the degree you have had it, it would have made sense to pull the crank and have it machined like you ordinarily would for a typical bottom end rebuild and you would have caught any problems there. I'm guessing this is in your immediate future anyway. But I bet there is more damage there than you anticipate right now. With that kind of heat, who knows what else is smoked in there.

Frankly if you are looking for the quickest, most economical way out of this, I think far and away the best bet is to find a replacement engine you can get cheap with a worn top end but good bottom end, then transfer the jugs and pistons/rings from your rebuilt top end to a free-spinning bottom end. If your original crank was bent or if the rod journal damaged on that side then you are probably in it for at least one new rod and of course rod bearings for the replacement engine. However given your current conundrum and the amount of time you've put into this, I think I'd carefully inspect any replacement bottom end and probably go for a wholesale rebuild including new main bearings and machining the crank. In for a dime, in for a dollar.

Good luck, and at least you are learning a lot in this process! I admire your willingness to dig in and fix this yourself.

Offline Bluesmudge

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #9 on: November 15, 2019, 03:04:31 PM »
Frankly if you are looking for the quickest, most economical way out of this, I think far and away the best bet is to find a replacement engine you can get cheap with a worn top end but good bottom end, then transfer the jugs and pistons/rings from your rebuilt top end to a free-spinning bottom end. If your original crank was bent or if the rod journal damaged on that side then you are probably in it for at least one new rod and of course rod bearings for the replacement engine. However given your current conundrum and the amount of time you've put into this, I think I'd carefully inspect any replacement bottom end and probably go for a wholesale rebuild including new main bearings and machining the crank. In for a dime, in for a dollar.

Good luck, and at least you are learning a lot in this process! I admire your willingness to dig in and fix this yourself.

I second mr72's opinion. As much as I commend your for digging this deep to find the problem, good used engine parts for the GS500 are just so cheap it seems much easier to just swap in a low mileage engine or compile an engine from known good parts. For example, there is a complete engine on eBay right now for $450 shipped. I've purchased entire top ends for ~$150.
« Last Edit: November 15, 2019, 03:06:25 PM by Bluesmudge »

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #10 on: November 15, 2019, 06:34:22 PM »
Don't know what fixed it, took the whole engine apart and reassembled the entire thing and couldn't find any obvious errors.

Idled perfectly, nothing wrong. Let it sit for 2 minutes to burn off some oil i had on the exhaust headers and then gave it a rev to 7K.

Slowly moved from 1.5k to 7k (8ish seconds) and the motor made a loud CLUNK, heard some metal shards fall to the bottom of the motor and it's seized now.

Great :)

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #11 on: November 15, 2019, 07:12:17 PM »
Just FYI, I have no direct experience rebuilding an engine-- just being logical trying to read the original post and boil this down:

1. you discovered a broken piston skirt, decided to replace both pistons, both rods and the rod bearings
2. while disassembled, the crankshaft had resistance to 30 degrees of motion *while no rods or pistons are installed*. But you assembled and tried to run it anyway.
3. pulled it apart again, you found metal bits in there, attempted to sand it smooth and reassembled
4. engine now has a loud knock and mechanical shake

Is that about right?

Because if so, I'd say the crank is probably bent, main bearing is scored or spun, which would tear up the bore in the block, etc. One end of the crankshaft is very scorched. If it were me, I would have never reused that part, and I bet there is additional damage to the bore where the crank seats in the block.

While it was apart to the degree you have had it, it would have made sense to pull the crank and have it machined like you ordinarily would for a typical bottom end rebuild and you would have caught any problems there. I'm guessing this is in your immediate future anyway. But I bet there is more damage there than you anticipate right now. With that kind of heat, who knows what else is smoked in there.

Frankly if you are looking for the quickest, most economical way out of this, I think far and away the best bet is to find a replacement engine you can get cheap with a worn top end but good bottom end, then transfer the jugs and pistons/rings from your rebuilt top end to a free-spinning bottom end. If your original crank was bent or if the rod journal damaged on that side then you are probably in it for at least one new rod and of course rod bearings for the replacement engine. However given your current conundrum and the amount of time you've put into this, I think I'd carefully inspect any replacement bottom end and probably go for a wholesale rebuild including new main bearings and machining the crank. In for a dime, in for a dollar.

Good luck, and at least you are learning a lot in this process! I admire your willingness to dig in and fix this yourself.

Thanks for this.
There was only resistance in the rotation with the original conrods on. Once they were replaced with new bearings rods and pistons it was perfectly smooth.

There was a bit of shrapnel between the con-rod and where the counterweights are on the crankshaft. A bit of sandpaper and all was well.

Gonna strip the engine AGAIN today to see what caused the seize/how much damage is done.

I live in New Zealand and there are virtually no spare parts here. Shipping fees from the UK (where parts are cheap) are absurd. Paid $100 for both pistons (with conrods) but had to pay $70 shipping 😂


Thanks everyone.

Offline mr72

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #12 on: November 16, 2019, 01:30:04 PM »
Sorry to hear that. I hate to say it but I bet you find a bent rod and broken piston skirt. The original root cause was probably not fixed. But I hope I'm wrong.

Offline Kylll

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #13 on: November 17, 2019, 04:00:15 AM »
broken cylinder sleeve, completelly annihilated piston. haven't had time to fully disassemble.

Offline The Buddha

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Re: New bike, terrible rattle/shake at 3500+ RPM
« Reply #14 on: November 20, 2019, 01:51:45 PM »
found some shrapnel between conrod and crankshaft, sanded it down and it was perfectly smooth.


I don't believe you can do that by hand - and sanded down and perfectly smooth don't mean jack ... your hands find stuff smooth, doesn't mean you'd retain oil film at pressure and temperature. No oil film = adios.

It has to be turned, and has to be not out of round more than a 10,000th or 2 of an inch, and cant be under whatever the bearing spec etc etc is. Then its polished in a crank polishing machine - not by hand.

Its all gotta be mic'ed and put in spec, and you have to get the right bearings for it, and a lot of cases you can not find bearings in those sizes. You can turn and polish anything, if its more than 1 size under - and you were blessed to start with nothing but A and B bearings in the thing originally, you may get by with B and C - but if you had any C or had a broken rod beat a crank - you're done, you can turn and polish that shiny beautiful and in spec, but if you're under that C bearings ID spec, you're out of luck.

What are those A and B letters ??? Look at the back of the motor, right under the airbox - you' see A and B - I've personally never seen a C, but I'm sure its likely available, but if not, then no rebuilds are possible unless you start with all A, a worn GS with A and B bearings if C is available, can have 1 crank rebuild, a GS with any engine damage - rod/piston etc damage - nope, its done.

Cool.
Buddha.
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