Alright guys, this post is kinda for my mate whos Yamaha XT350 ran low on oil yesterday. He snapped his manifold off at the exhausts ports and ran it like this for a week or so, apart from busting performace due to the lack of back pressure will this have caused any damage? After he got his new manifold we went for a cruise, the bike was much better due to having backpressure but after a couple of miles it started making a metalic whring sound and lost maybe 30% power.. We stopped at a garage, the first thing I did was check his oil level, he hasn't checked it ever (dumbass!) but last time I saw it a month ago it was reading medium. When I checked it after it lost power there was bugger all, we topped it up with some 4t oil and it took 500ml to bring it back up to medium. The bike is really hard to start now and the compression seems a little lower since its easier to kick, I can hear a lot of tapping from the head (i think), it still goes pretty quick but like I said maybe 30% slower than it used to.. its also burning oil pretty bad now, it never used to as it had a full rebuild a month ago....I figure some hefty dmage has been done to the head like scored camshaft and bearing hence the tapping, what would cause the oil burning? valve stem oil seals? would these bust if it ran low on oil? I'm kinda hoping the rings are ok as its still pretty quick.. anyone know the best way to go about getting it sorted/ideas whats gonna need fixing? I'm not to well up on bikes...although i figure its hard to start becuase the spark plugs are probably now covered in oil...cheers for any responce, we're tryin to sort it out on budget...

 

ttt

 

I don't see too much chance for any damage from running w/o the emanifold. I would say worn tappets/cam lobe contact caps are the cause for the tapping. During a period of oil starvation, the clearance surfaces are worn and thus creat enough of a gap that there is no contact during blank cam phases and contact as the cam profile becomes engaged. As for the oil burning, bad valve stem seals tend to only burn large amounts of oil when the engine sits cold for awhile. Upon startup, the high vacuum pulls a lot of the oil that has settled onto the seals into the cc. Really bad seals could allow oil consumption during running although it should be more noticeable during idle and part throttle situations as opposed to wot. Pull the plugs and see what you get. Btw, consider dropping the pan and checking for any material in the oil. The whirring may be the beginning of the end for a bearing.

 

ok dude, cheers for the help... it does only smoke when at idle/decleration so i'm figuring valve stem oil seals like you say... i figure the rings are still sealing well becuase there is a fair amount of power on acceleration with no smoke... hopefully the large tappet clearances are responsible for the slight power loss...the whring noise has gone now but i guess only time will tell if a bearing has taken some crap... thanks for the help anyways...will have a look at the pan sooner or layer when we get round to it... i sure hope theres nothing in it!

 

If your valve seals are REALLY bad, it is possible for you to be losing compression there and thus... power. Whirring is usually metal on metal... either bearings or something int he valvetrain. Good luck

 

Well... here's the update. Due to money problems and the bike running fairly well my friend has been riding to work for the past few weeks without checking out the damage. Last night he decided to travel up to London from the south coast of england which is around 100miles. With a friend on the back going 70mph on the motorway at night the engine seized, the back wheel locked sending the bike into a slide across the motorway. They both came off and by some miracle managed to get up straight away and run off the motorway. They spent the night in a nearby hospital, my friend suffered a slight chip to a bone and some grazing, the guy on the back got away with some heavy grazes. Safety gear was fairly light, gloves, helmets, decent moto-x jackets and jeans. I can't believe they got away with it so slightly, its a mriacle they were not killed. Just a warning to anyone in a similar situation.

 

Wow. What a tragic case of not maintaining your stuff.

Tell your friend to get something he can afford to maintain - I've got a 49cc Zuma for sale.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Aleister Crowley &raquo;</TD></TR><TR><TD CLASS="quote">Wow. What a tragic case of not maintaining your stuff.

Tell your friend to get something he can afford to maintain - I've got a 49cc Zuma for sale.</TD></TR></TABLE>

Yep, for sure. I guess this all stems from a broken manifold which he didn't fix for two weeks causing exhaust valve damage which resulted in the oil running low, he never checked it so thats when the serious damage started, never got his bike checked out after it started running bad and a few weeks later the engine seized almost killing him. The bikes a write off, since he only had 3rd party ins. hes lost £1000. I hope he learns now, skimping simple cheap maintence is so much more expensive in the long run and on a bike it could cost you your life.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by goodbyegti &raquo;</TD></TR><TR><TD CLASS="quote">

Yep, for sure. I guess this all stems from a broken manifold which he didn't fix for two weeks causing exhaust valve damage which resulted in the oil running low, he never checked it so thats when the serious damage started, never got his bike checked out after it started running bad and a few weeks later the engine seized almost killing him. </TD></TR></TABLE>

i think having the exhaust manifold removed could have accelerated the oil burning. fresh air mixing with the exhaust gases when the valve opens makes things get very hot, we used to see people burn the pistons on the exhaust side of a 2-stroke motor without a muffler. except in this case it was the valve, which became damaged and damaged the vale stem seals causing more oil to burn.

i hope everyone recovers fully. that really sucks. expensive lesson to learn.

 

thanks for that, i spent ages thinking about why the oil ran low so quickly in the first place as it had a full rebuild maybe 3k ago, someone else i spoke to hinted at valve damage but you've clarified it now, i'm sure everyone will be fine, the main reason i posted back was to warn people of the possible consequences of not maintaining their bike...my friend learnt the hard way!