Author Topic: For XBR500 Boffins  (Read 1586 times)

Nell

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For XBR500 Boffins
« on: December 10, 2008, 04:10:11 PM »
Question for any XBR engine aces.
Just replaced the XBR engine with one overhauled and rebored 2000 miles ago. (Used original head after valve seats recut and new stem seals fitted).Engine started immediately and idled nicely. Ran it for 4-5 minutes then blue smoke started coming out of exhausts and got worse until engine stopped despite blipping the throttle. Tried again with new plug, same result.
Stripped engine:-
Inlet valves and breather clean, exhaust valves sooty.
No wear in cylinder bore, piston and rings, (rings correct way up, gaps OK).
Removed and checked oil pump, oil tank, oil lines and seals. All clear and pump collecting oil and giving pressure. Put it all together. started first time but same problem as before, traces of blue smoke after 4-5 minutes getting worse until plug fouled up and engine stopped.
Any ideas please?

guest7

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Re: For XBR500 Boffins
« Reply #1 on: December 10, 2008, 05:04:22 PM »
You did smash a glass of Saki over the rocker box before starting it didn't you? I'm not superstitious, but I do it every time  ;)

Seriously though, I think some of the forum eggheads are required here. I'm sure they'll be along soon
GC

themoudie

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Re: For XBR500 Boffins
« Reply #2 on: December 10, 2008, 11:21:32 PM »
Aye Nell,

Have a read of this thread:http://www.thumperclub.com/smf/index.php?topic=866.0

Then go and get the gear on and ride it, if you keep doing what you are doing you'll have to have the barrel honed again at the least and at worst another rebore plus piston. I hope this helps you.

Regards, Bill.

guest7

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Re: For XBR500 Boffins
« Reply #3 on: December 10, 2008, 11:35:01 PM »
Here's themoudies link... as a link:
http://www.thumperclub.com/smf/index.php?topic=866.0


Cheers
GC

Nell

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Re: For XBR500 Boffins
« Reply #4 on: December 11, 2008, 10:57:53 AM »
Thanks for pointing out the link, it's an interesting theory but I would agree that the engine needs to be at working temperature before giving it a thrash. I will try the procedure if I can get the engine to run long enough without cutting out or disappearing under a cloud of blue smoke. Thanks again, I'll let you know.
p.s. The saki didn't work.

Steve H

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Re: For XBR500 Boffins
« Reply #5 on: December 11, 2008, 12:14:48 PM »
Blocked breather is another possibility

andy230

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Re: For XBR500 Boffins
« Reply #6 on: December 11, 2008, 12:48:34 PM »
just an idea....  (i know nuthing of xbr motors!!)

are we presuming this is oil?  Then probably over oiling to the rocker gear???  Even on a newly bored cylinder it shouldn't be letting enough oil get by the rings to foul the plug....

or is it possible that it is over-rich re fuel, and fouling??  Carb shot?  ( I also know nowt of xbr carbs!)

good luck!

a



Nell

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Re: For XBR500 Boffins
« Reply #7 on: December 11, 2008, 07:40:50 PM »
Steve H
I checked the breather hose and blew air through the stack pipe when I had the cover off to look at the oil pump. All clear.
Andy230
It appears to be oil as the smoke is blue and the plug very sooty and oily when the engine stops. I overhauled the carb at the same time as the engine change and also tried it with a known spare carb on the second attempt. The rocker area didn't seem over oiled when I took off the cover and the valve seals are new and looked OK, but it's a possibility.
Thanks guys, I'll try again and if no joy keep searching although it's pretty cold in the garage at the moment. Roll on better weather.

Steve H

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Re: For XBR500 Boffins
« Reply #8 on: December 11, 2008, 08:29:07 PM »
- Oil control rings on piston assembled correctly ?
- Cracked piston ?, what make was new piston
- Ring groove too small, locking rings in position when piston warm ?
- Ring end gap too small ?
- Oval bore
- Tapered bore

guest288

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Re: For XBR500 Boffins
« Reply #9 on: December 12, 2008, 08:33:53 AM »
Has the motor been honed or sleeved?
If theres a sleeve, it could be moving when its warmed up allowing oil to pass?

guest295

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Re: For XBR500 Boffins
« Reply #10 on: December 12, 2008, 09:07:33 AM »
The worst thing you can do to a rebuilt or new engine is to let it idle for a long time. The cylinder warps out of round and there isn't enough pressure to force the rings against the walls. Don't do that! As soon as it's running, snick it in gear and ride it. Keep air moving against the front of the cylinder, 35mph is a good minimum. When it's warm, put some pressure on it to force those rings out. Don't drop below 3000rpm. If you've got a handy hill, ride to the bottom and stop, let the engine cool for several minutes, then accelerate up the hill as hard as you can without going over (say) 6500rpm. Then do it again.

Nell

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Re: For XBR500 Boffins
« Reply #11 on: December 12, 2008, 11:00:32 AM »
Steve H
- Rings were checked and gapped.
- Bores parallel and round. Checked with bore gauge top, centre and bottom at 45 degree intervals.
- Cracked piston? It's a Honda item that looked OK visually when fitted but I did not inspect it closely
  Could be a small crack that opens up when hot. Looks like a dismantle job again but thanks, it's a
  good point.
Dave500
- It's a 20 thou oversized rebore, no sleeve.
GB500nz
- I cannot get the engine to keep going long enough to give it a decent run, it's fine for several
  minutes before the smoke starts then it cuts out. Anyhow thanks for the info, I'll keep it in mind
  when I eventually get it going.

andy230

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Re: For XBR500 Boffins
« Reply #12 on: December 12, 2008, 12:44:16 PM »

- I cannot get the engine to keep going long enough to give it a decent run, it's fine for several
  minutes before the smoke starts then it cuts out. Anyhow thanks for the info, I'll keep it in mind
  when I eventually get it going.

Is it a very cold plug which is in there???  Would that be sufficiently serious to cause it to foul?  Unlikely, but this is an enigma...

Don't XBRs tend to have cracks in the head??  Could that be it??

a

themoudie

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Re: For XBR500 Boffins
« Reply #13 on: December 12, 2008, 09:45:23 PM »
Aye Nell,
 "I cannot get the engine to keep going long enough to give it a decent run, it's fine for several
  minutes before the smoke starts then it cuts out."

To much oil?

Sticky oil pressure ball, sump filling up with oil because the return side of the pump isn't scavenging?

Any bleed screws to open to remove airlocks?

Old oil line internal collapse due to perishing or is there a lump of SH :-X TE in the return pipe?

Any internal strainers/mesh filters which might collapse and obstruct return to oil tank?

Never been in the guts of an RVFC, but I'd go from easy to get at, pull off, blow or poke through bits before dismantling.

Too much gasket goop or a gasket blocking a drilling? RTV etc stick like  :-X to an army blanket and pattern gaskets don't always have the right holes in the right places or the right holes at all ???

If nothing obvious, get the gear on and go for a ride, even if it only manages 1 mile. Revving or ticking over with no load is not the same as riding the beast and applying load to all the parts. I am not saying you should thrash it, because it won't be up to working temperature, but it needs light work from the start. Your quote reads as though it is an accumalative malaise and even "several minutes" riding rather than waiting for the blue reek could make all the difference.

Sally (SRX600) after her rebuild got caught at lights after about 5 miles and after sitting ticking over for 2 minutes started producing clouds of blue smoke! ??? Stopped her, pushed her to the side of the road and let cool for 15 minutes. Started her up and the rode for another 20 miles with no stops to get home. No smoke and has been fine now for ~12K miles.

Please let us know what results you have.

All the best, Bill.

Nell

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Re: For XBR500 Boffins
« Reply #14 on: December 14, 2008, 05:34:51 PM »
andy230.
Plug is Honda recommended and no cracks in head.

themoudie.
Thanks for your ideas:-
- Oil level is top of dipstick marking.
- Will change oil pump (see footnote) although the one fitted seemd to be picking up and dispensing oil when checked initially.
- oil flowing from cambox union and oil lines clear.
- Oil filter replaced and crankcase mesh filter clear. Oilways clear (compressed air)

PLAN:-
Remove head and barrel, check piston for cracks, check rings and grooves again. (bore checked last time top to bottom - within 0.001").
Fit cylinder barrel and piston from old engine with a spare head I have.
Change oil pump for serviceable spare on shelf.
TRY AGAIN
Take removed cylinder, piston and head to local classic bike machine shop for further assessment and advice.

Thanks to eveyone who took the trouble to reply, I didn't expect such a big response. I seem to be heading for a doze of flu but will let you know the eventual outcome.