XBR compression

[mthee]

Bike's been standing 3 weeks, so I thought I'd fire her up to cheer myself up. So I know from SteveC#222 that these bikes inexplicably lose compression when left standing, but how long after they fire up, does it return?
Having turned her over a few times on the kickstarter, ignition off, I got her going on the button, 3rd go and she idled at 2k for a few minutes whilst I basked in the smell of burning ACF50! Turn her off, then go to kick her without using the decompressor lever and find I can ease her past TDC just by standing on the kickstarter with my 10 1/2 stones. Should I be worried about my rings and/ or guides?

[timbo]

I wouldn't be too worried, unless you discover she's using a lot of oil Matt.

[mthee]

Last trip was 260 miles and she used 80ml, so how's that sound?

[timbo]

I'm not really sure Matt. We need someone with more XBR experience to comment.

[SteveC#222]

Probably about right, they do use a little bit. If it's running OK and not smoking I wouldn't worry too much about the compression.

[themoudie]

Aye Matt,

Based on my experience with the SRX, use it more often and keep it topped up after 500 - 1,000 miles. When you get home from a run, just let the motor idle for a couple of minutes and then measure the oil using the approved method for these dry sump motors. Top up, if required and a wee toothbrush of SAE80-90W gearbox oil or chainsaw chain oil round the inside of the chain and leave to sink in as the chain cools. These motors 'breath' a bit as they age, and 'Sally' slurps about 200cc in 500 - 750 miles, there is also a weep from the front of the cylinder head. The weep 'll get sorted the next time the head comes off. 

My regards, Bill

[mthee]

Thanks for the reassuring guidance. It does feel good on the go, but I must take some notice of the exhaust gas colour on starting. I'll have onethecheap's original automatic decompressor fitted once I get a gasket, so presumably, it'll feel different standing on the kickstarter.

[JOOLZ]

I have had rings stick on the XBR, if it starts give it a good long ride and they will free themselfs, XBR's do use a fair bit of oil, I dont think yours is using more than usual. There is a cure to lower the oil consumption, fit a one way valve to the breather problem solved. I use a one way fuel check valve with a 12mm pipe fitting, dont fit it the wrong way around or you will blow all the seals out

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[mthee]

Sorry Joolz, I forgot to add my thanks for this great tip - ta! 

[mthee]

Hi Joolz, I thought I understood how your tip to use a one way fuel check valve works to reduce oil consumption. However, having just received the valve in the post, I realise that I haven't grasped the theory at all. Please would you enlighten me?

Hang on a tick, is this it?

http://www.eurospares.com/sucker.htm

So I have to install the valve with the arrow pointing away from the crankcase? Last question is about the quality of the valve and maintenance. I went for this one;

https://www.amazon.co.uk/gp/product/B00YOK9SVE/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

Too cheap?

Do they need cleaning periodically? Thanks.

[JOOLZ]

Thats the idea, the part you have bought is the same as mine, arrow pointed away from the crank case, I havent had mine fail in the 5 years I have been using it.
Yes as the piston moves up the bore a low pressure area is formed in the crank case and the valve is shut , when the piston comes back down its stroke the valve opens and allows any excess pressure out. I have found out however that with the engine running the crank case pressure is always below atmospheric pressure. There a a couple of bonus's of this, the rings are forced tighter in the bore, any weepy joints in the cases are cured and the oil has less tendincy to foam with any air, its also worth about 1/2 a hp extra not that you would notice much. I hope that helps

[mthee]

Thanks, Joolz, I'll get it installed. What about cleaning the valve? I have no idea about their makeup. Will there be a risk of clogging? With my seals at stake, I'd hate to get this bit wrong!
Just had a look - my current breather tube is routed to vent over the front sprocket. From your photo, yours looks to be going elsewhere?

[JOOLZ]

I havent needed to clean my valve yet, but a soak in petrol will be all thats needed to clean it, my breather pipe just vents near the rear mudguard

[mthee]

Thanks. I did wonder whether you'd plumbed your pipe into into your exhaust to get extra pull on the crankcase pressure, as described in that article, or whether my venting over the front sprocket was verboten for some reason.

[JOOLZ]

It doesnt matter where you vent it. No I havent plumbed it into the exhaust, I thought about it but just fitting the one way valve cured all my problems