Author Topic: Big bore XBR???  (Read 1475 times)

blew

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Big bore XBR???
« on: October 12, 2009, 08:40:47 PM »
I have read that it is a straightforward job to fit a 600 barrel and piston to an xbr,with a thicker base gasket to keep the compression ratio sensible.Has anyone done this?Are there any pitfalls?The intention would be to produce a torquey motor,not a racer.Any comments will be appreciated.Thanks.

guest7

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Re: Big bore XBR???
« Reply #1 on: October 12, 2009, 09:07:52 PM »
There used to be a superb XBR FAQ on the Thumper Page that covered all the options.

you can see it HERE


Also check out Randall Zempell's article on race prepping a GB500
GC

SteveC#222

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Re: Big bore XBR???
« Reply #2 on: October 12, 2009, 09:20:17 PM »
Hi Blew,

Also check this out - I would think parts are still available but not sure about the current exchange rate. It's for the GB500 but the XBR would be the same.

GB500 Hop Up

...you can also fit the 650 Dominator engine.

...oh yes, I seem to remember the gudgeon pin diameter is different between the XBR and the XL and you need a bush making up...I think it's in the link GC gave you.
« Last Edit: October 12, 2009, 09:24:46 PM by SteveC#222 »
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blew

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Re: Big bore XBR???
« Reply #3 on: October 12, 2009, 09:48:23 PM »
I have read the Thumperpage articles-that's what gave me the idea.Those articles state that the GB and the XL have a 24mm small end.My XBR is very thirsty on oil,and I have obtained a pristine XL barrel and piston,so I hoped they would be a straight swap,giving some extra grunt as well.Apart from the higher compression,I wondered if there were any potential problems.Will the crack-prone XBR head stand it?I'm not interested in racing or higher revs.

guest7

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Re: Big bore XBR???
« Reply #4 on: October 12, 2009, 10:14:42 PM »
The XBR head may be crack-prone, but I've never heard of those cracks actually causing any problems. I have an engine here that has done over 60,000 miles since I discovered the cracked head.

GC

SteveC#222

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Re: Big bore XBR???
« Reply #5 on: October 13, 2009, 07:55:47 AM »
The extra 100cc should give you a useful amount of extra torque - probably more noticable if your engine is already a bit tired. If you were looking for performance, then the big bore on it's own would probably not be worth the effort but, as it sounds like your due for some engine work anyway and you have the parts you may as well go for it.  

You're using Honda parts, so they will be well made, over engineered and under stressed. I wouldn't think you will increase the compression ratio - in fact it may even drop a little and the XBR engine is based on the XR600 engine anyway which is pretty bomb proof. The only possible downside may be a slight increase in vibration due to the extra weight/mass of the bigger piston being out of balance with the crank/counter weight but I would think that would be pretty negligable  - go for it!

As far as I understand it, apart from the little end, it's fairly straightforward. I'm sure someone on the site has done it a while ago (Mixerman?) - might be worth looking through some of the old posts or doing a search.


Try shouting or PM'ing TurkeyUK - I know he tweeks XBR's and may be able to advise you.
« Last Edit: October 13, 2009, 07:59:15 AM by SteveC#222 »
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guest7

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Re: Big bore XBR???
« Reply #6 on: October 13, 2009, 06:05:08 PM »
My 650 XBR wasn't any faster, but it fair belted out of corners because of the extra grunt which meant a faster overall time anyway.

GC

blew

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Re: Big bore XBR???
« Reply #7 on: October 13, 2009, 07:27:45 PM »
Thanks for the information.I'm pleased with my xbr-I enjoy riding it,and it brings back old memories of simpler days.It almost always starts first kick,it idles ok.,it will hold 80 when the road is clear,and so on,but it burns oil like a 2stroke (100 miles per pint!!).I intended sorting the top end over the winter,but an XL barrel and piston came my way,and I thought some extra grunt would not go amiss.Even when out with friends on bigger,faster machines,it keeps up well and it's fun to ride.A bit of vibration reminds me of old times too!I'm probably regressing into childhood slowly,but I think it's so easy to ride-no worries about losing my licence on the straight bits or disappearing through the hedge on the corners.No worries-enjoy the ride.

guest27

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Re: Big bore XBR???
« Reply #8 on: October 13, 2009, 07:55:29 PM »
Thanks for the information.I'm pleased with my xbr-I enjoy riding it,and it brings back old memories of simpler days.It almost always starts first kick,it idles ok.,it will hold 80 when the road is clear,and so on,but it burns oil like a 2stroke (100 miles per pint!!).

My stinkwheels ave been in touch with their lawyer and will be in touch soon.  None of them has ever gone through a pint per 100... ;D

R

blew

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Re: Big bore XBR???
« Reply #9 on: October 13, 2009, 09:59:29 PM »
Rog,try opening the throttle on them!The smokiest bike I ever owned was an A65 Spitfire,which wet-sumped occasionally.I once went camping with the BSA Owners Club to the Black Forest.The Spitfire wet-sumped one night,and was a pig to kick over the next morning.She eventually gurgled into life,and I had to leave her running on the stand to clear the crankcase.Several tents disappeared under the resulting blue cloud,and uncouth language was heard from the invisible depths of the fog.I was banned from starting her afterwards until the neighbourhood was cleared.Who needs 2strokes??Just as well Greenpeace wasn't around.

guest564

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Re: Big bore XBR???
« Reply #10 on: October 21, 2009, 03:21:07 PM »
Fitting the 600 barrel isn't a straight fit, you need to open up the crankcase mouth to accept the bigger liner. You want the barrel from an XL/XR600R (589cc not 591cc???), the XL600LM engine has a different stroke and the barrell is 1mm taller, the LM also has a smaller diameter piston and a smaller little end. If you are running an XL piston then the compression will be considearbly lower, a Wiseco piston will raise the CR and is pretty much the exact weight of the original 500 piston.

blew

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Re: Big bore XBR???
« Reply #11 on: October 21, 2009, 04:43:35 PM »
I stripped the top end of my oil-burning xbr yesterday.There had been a blow-up at some time,since the piston crown and cylinder head showed some gouges.When I removed the barrel and piston,the top ring was stuck in its groove,and the end gap of the second ring was 35 thou (service limit 26 thou).That explains the oil burning.I also discovered that the cam was the same as an XL-lobe height approximately 31mm,the XBR should be approximately 34mm.Anyway,I rebuilt it with the XL barrel and piston.I took it for a brief spin today - terrific torque at all revs (mild cam ??),but full throttle was impossible due to clutch slip.I kickstarted it readily before going out,but afterwards the compression seems to have increased.Once the piston approaches TDC the kickstart stops dead.I'll have to do some weight training on my right leg!!The starter motor is wheezing feebly too.First impressions very good,but I need to sort out the clutch now.I've no idea yet what the compression ratio is,but it's considerably more than it was with the knackered piston.I'm unsure whether to look for an XBR cam,or keep the current cam for the extra grunt.

guest564

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Re: Big bore XBR???
« Reply #12 on: October 22, 2009, 01:09:05 PM »
My starter motor turns mine over reasonably well with a 11.6:1 CR, I have no decompressor and can stand on the kickstarter without it moving. Does the cam show any signs of having been reground? that would explain the apparent difference in lobe height. From what I remember the XL and XR cam timing are pretty much the same, the bigger capacity reduces the rpm at which peak torque occurs.
Did you use the 600 head gasket?

blew

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Re: Big bore XBR???
« Reply #13 on: October 23, 2009, 07:35:31 AM »
I followed the advice given in the article on GB500 tuning.I fitted two base gaskets and used a 600 head gasket.It kicks over fairly easily when cold,but gets noticably stiffer when hot.The head showed signs of damage at some time,and one exhaust valve seat had been changed.I presume the seat and the cam were changed after the blow-up.The cam seems original,not reground.Before I stripped the top end,the engine was reluctant to rev out.It would pull six in 4th easily then run out of breath.It was happy to stay at 80 as long as the road allowed,but the most I ever saw,after a good run-up,was about 90.With hindsight,I presume that was a combination of a mild cam and a knackered piston.I'm not too concerned about top speed-I have another bike for that,but I would like it running correctly.I quite like the grunt of the engine as it is now-loads of torque from low revs in any gear.The clutch is now a problem - new plates,heavy duty springs,or both???Would I lose much of the bottom end if I fitted an XBR cam?

blew

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Re: Big bore XBR???
« Reply #14 on: October 23, 2009, 07:49:26 AM »
I was actually a bit surprised how simple it was to change the barrel and piston.The piston is 100mm,and the small end 24mm.The barrel fitted straight on and everything bolted back easily.The ring end gap was 13thou,and the piston was a close fit.The old piston had one seized ring,and the other had a gap of 35thou,and the piston felt rather loose.That explains why it used a pint of oil every 100 miles!!