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 Poorly RGV

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andysej



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PostSubject: Poorly RGV    Wed Sep 19 2018, 21:12

The last time I rode my RGV250M was at Cadwell back in June. And I had absolutely fantastic fun. However I was getting a little concerned over the roughness of the engine at low revs. When pulling away as the clutch fully engages you get a slight shudder which soon disappeared as the revs rise above about 3.5K. It then runs smoothly right up to the redline. To be fair it has done this since I rebuilt it back in 2013, but more recently I am hearing a squeak as the engine picks up from tickover. So now the season is over I decided to investigate.


With the bike up on the stand, I set about removing the bodywork. The first thing I saw as the left hand panel came off was a crack on the engine subframe, all the way around at the top left hand mounting (sorry no photo of this). So I thought I'll have to strip the engine to see whats amiss.


The next job was to remove the engine, but to my horror  affraid as I started to undo all the mounting points I found this.

Two pieces of aluminium that used to be engine mountings.


These are the main engine supports. It looks like the only thing holding the engine in is the exhaust pipes!




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Rob62
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PostSubject: Re: Poorly RGV    Wed Sep 19 2018, 21:24

It will be much smoother once you get it repaired... roll on next spring Very Happy
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andysej



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PostSubject: Re: Poorly RGV    Wed Sep 19 2018, 21:32

So I need to get the frame repaired and then to determine the cause of the vibration. I have now stripped the engine completely and assembled the main crank casing back into the frame complete with a replacement sub frame (eBay). Today the frame went to a repair shop that specialise in aluminium bike frame manufacture and repair. They are going to manufacture and fit new heavier gauge mountings.

Here's the assembly as delivered to the frame specialist.



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andysej



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PostSubject: Re: Poorly RGV    Wed Sep 19 2018, 21:50

While the frame is away being sorted I need to identify the root cause of all this damage. As I stripped the engine there was no signs of distress anywhere. The power valves, pistons, bores etc all look good. The final drive and flywheel were all nicely secure. The only thing left to check is the crank run out. According to Suzuki the max run out at the outer bearing journals is 0.05mm (2.1/2 thou). But to check this you need to remove the outer bearings. I'm not going to do that. So I set the crank with outer bearings on vee blocks and measured the run out at the final drive and flywheel landings.

There is 0.06mm run out at the flywheel side (same side as crack in sub frame). T'other side is ok. Trouble for me is I'm not really experienced in these cranks and don't know what's acceptable. So It's off to "The Tuning Works" for them to have a look. I reckon it will need tweeking.






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Wolfie
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PostSubject: Re: Poorly RGV    Wed Sep 19 2018, 22:06

I'd have been quite happy with 0.06 runout until you mentioned the recommended amount. Somehow I can't see that amount vibrating enough to break the mountings but I'm no crank expert either.

I'm still hopeful about having solved my own vibration with the recent stripdown, unfortunately just at the moment I'm running one (heavier) Kawasaki Piston with two Wossners so it's difficult to be certain.

Hopefully your broken engine mounts are simply that and not an underlying problem.

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andysej



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PostSubject: Re: Poorly RGV    Wed Sep 19 2018, 22:14

Hopefully you're right Gra. The crank was built by SEP at Kegworth. They've a good reputation. The engine is smooth at 10,000 rpm. Looking at the fracture surfaces, the cracks have been there a long time with final complete fracture very recent. Maybe I missed the cracks when I rebuilt it 5 years ago, I never carried out any NDT on the frame. My eye sight is shit these days. Better to be sure though.
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Rob62
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PostSubject: Re: Poorly RGV    Thu Sep 20 2018, 21:08

I cant see 0.01 over tolerance causing an issue. 0.05 is only 0.002” by the way. I suspect that the fracture is just metal fatigue due to age. Having said all that, in precision engineering terms, 0.002” is quite a bit out of true so maybe a crank tweek would be a good idea.... isn't bryanH a crank expert? He’s a regular visitor on here.... and fairly local too (Hull) if I’m not mistaken.
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Bryan H

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PostSubject: Re: Poorly RGV    Thu Sep 20 2018, 22:28

Ideally you need to measure the runout from the centre of the crank to each end as 0.06mm runout could be anywhere across its entire length and potentially 0.03 at either end. Having the bearings still attached doesn't help and tends to exaggerate the reading. I had a V block cut in half so I could measure each side accurately from the centre particularly for X7's and RG's. Looking at the pics however it does appear that the runout is at its max where the big end pin is and this would suggest that the webs on that side are slightly out of parallel. To fix this you'll need to put the offending webs in a vice (at the opposite end to the crank pin) and give them a slight squeeze.

As the guys have said 0.06mm runout wouldn't cause the engine mountings to fail. Personally I'd just re install it in the engine Very Happy
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andysej



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PostSubject: Re: Poorly RGV    Fri Sep 21 2018, 14:43

Thanks for the thoughts guys. I have no experience of crank building so it's helpful to have your comments. I have today had my crank checked over by Sean at "The Tuning Works". He recommended refitting into the engine as is. Thumbs up
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Rob62
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PostSubject: Re: Poorly RGV    Fri Sep 21 2018, 22:19

Sounds like good advice Very Happy
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andysej



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PostSubject: Re: Poorly RGV    Mon Sep 24 2018, 22:47

Had a message today saying my frame repair is complete. I'm going to collect it on Wednesday. Hope they've done a good job Very Happy
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Wolfie
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PostSubject: Re: Poorly RGV    Tue Sep 25 2018, 07:28

Thumbs up Thumbs up
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andysej



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PostSubject: Re: Poorly RGV    Wed Sep 26 2018, 18:30

I picked up my frame today. I must say Gav at GIA Engineering has done an excellent job and I am impressed. Thumbs up

They have dressed off all of the original weld, made new brackets, welded them and carried out NDT. All for a reasonable price (guess how much?)


Beefed up brackets, the original ones are very thin.


Nice welding.


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Rob62
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PostSubject: Re: Poorly RGV    Thu Sep 27 2018, 13:25

Nice job!! I guess at £300 ??
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Wolfie
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PostSubject: Re: Poorly RGV    Thu Sep 27 2018, 19:23

Oh dear.. you're gonna have to clean the engine now to match that lovely frame.
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andysej



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PostSubject: Re: Poorly RGV    Fri Sep 28 2018, 00:02

I'll clean it, but not too clean as it's not on show Very Happy
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andysej



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PostSubject: Re: Poorly RGV    Fri Sep 28 2018, 00:23

Rob62 wrote:
Nice job!! I guess at £300 ??

I thought maybe about that amount, but you're way off. £70 was the bill. Problem is I've now managed to find some other cracking that needs sorting so I've got to start again.

I had reckoned to look at the suspension mounting already knowing there is a common issue there. However I had a better look last night (with 2 pairs of glasses on) and this time I found cracks


Can you see cracks?


See them yet?


See them now?





The Tuning Works sells a replacement bracket ready to weld on which will make the job quicker.


Meanwhile I'll get on with rebuilding the engine. Smile
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Rob62
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PostSubject: Re: Poorly RGV    Fri Sep 28 2018, 23:42

You would have thought the frame specialist would have checked for those while he had it in his shop..... Shocked
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andysej



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PostSubject: Re: Poorly RGV    Sat Sep 29 2018, 09:49

Possibly especially if he'd seen it before. However in his defence I did tell him i'd checked it and it was ok.

I had initially looked at the main bracket welds thinking the cracking would be there. But I had to knock out the bushes from the bracket to see the tiny cracks. If you look on the images I hadn't removed the bushes when the frame went in for repair.

I should be more thorough and do some dye penetrant testing. Might do yet before I take it back.
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andysej



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PostSubject: Re: Poorly RGV    Tue Oct 02 2018, 20:30

Did a bit of NDT this aft. Can't see any other problems thankfully, but the cracked suspension mount shows up clearly. I have also bought a replacement bracket so another trip to the welders is on the cards.

Nice crack, easily visible with a bit of dye penetrant.


New bracket, a bit more substantial.


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Rob62
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PostSubject: Re: Poorly RGV    Wed Oct 03 2018, 23:01

Food for thought.....all those 1990’s 250 race reps out there with aluminium alloy frames.. I’ll get my magnifying glass to the NSR over the winter Shocked
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andysej



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PostSubject: Re: Poorly RGV    Wed Oct 03 2018, 23:12

Yes exactly. You've got to be careful when rebuilding ally framed bikes. It's easy to put a bit of stress on the frame which will result in cracks.

I'm picking my frame up from the welders for the second time tomorrow. I'll post some pics of the repair.
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Rob62
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PostSubject: Re: Poorly RGV    Thu Oct 04 2018, 13:24

not only stress generated during the rebuild but any stresses including normal flexing of the frame during operation.... Unlike steel frames, aluminium does not resist these stresses indefinitely.
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andysej



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PostSubject: Re: Poorly RGV    Thu Oct 04 2018, 13:53

Got the frame back again today. Another excellent job by Gav at www.giaengineering.co.uk




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Wolfie
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PostSubject: Re: Poorly RGV    Thu Oct 04 2018, 20:04

Shocked That's pretty neat... shame I haven't got an Ally frame.. Come on now there's still time to get it built and out on the road before the clocks go back.
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