I am now the owner of PO55 OTS; and very happy with this lovely bike - apart from the mystery of the disappearing oil! There is no evidence of oil leaking, it does not smoke but at the end of every ride ( usually about 50 miles of gentle, Cornish lanes) I have to add at least 100ml of oil just to get the level visible in the sight glass. After the last ride out, it took 300 ml, which is starting to get a bit concerning. Any ideas as to where the oil is going and how to stop it would be greatly appreciated.
possible stem seals if it was piston rings you would see slight smoke have you changed the oil recently if not makes sure when you do put the specified oil not too thin like 5 w 40 put 10w 40 its mot using too much as tho its old oil too thin try it
Yep, I have changed oil and filter recently, and always use the recommended 10w 40 oil! As this bike has done very few miles since it's 350 conversion, I would be surprised if it was the valve stems; but always a possibility - I was hoping not to have to go groping around inside the engine!
Just got back from a 70 mile ride out - the rider behind me said he could smell the burning oil on the overrun; although, apparently not actually smoking! I have checked the compression and that was within the specified tolerances. So looking more and more likely to be the stem seals - really hope it isn't a glazed bore! I took the spark plug out about a month ago and it looked pretty good, but obviously need to check it again. Looks like I am going to be busy.............
It you take the exhaust off after its been parked a while looking at the valve stems with a torch they tend to appear wet/oily . A fairly easy check . Also if the stem seals are crook after sitting for a while you may have a bit of smoke on first start up as the oil burns .
Inlet valves are a pain to check though as it involves taking the carb off
-- Edited by Ttboof on Sunday 29th of December 2024 08:42:35 PM
Susan , before you pull anything apart just check the crankcase breather is functioning, ie not blocked or a crimped or collapsed pipe. It would give high oil usage.
Cheers Tim
I have checked the crank case breather - all OK there. I have been advised to have a 'leak down test' before I jump in and start pulling the engine apart. Apparently that will help to establish which bit of the engine is causing the problem!
-- Edited by Susan Parker on Friday 3rd of January 2025 09:18:00 AM
I will let you know, Steve, when I have the result of the leak down test. My brother raised the point that if I have to get a re bore, presumably the new piston rings will not be standard? This is all getting rather alarming!!
if its had a 350 conversion no wear to rings possible glazed bore i dont think so doing leak test would not prove stem seals only poor compression valves worn bore piston rings glazed bore would not show low compression
So, it sounds like the leak down test would not show any more than the standard compression test that has been done, which showed that the compression was within accepted parameters. Looks like I am going to have to get in there and take a look!
Johnnyboy might be right with glazed bore if the bike has not really done enough hard work in it's early life. If there is not much/any smoke, it won't be anything catastrophic I think, but it looks like a tear-down is in order.
Do the valve stem seals anyway (use genuine only).
As Dan suggests, it is fairly straightforward to replace the sleeve if necessary, and will be much cheaper because gaskets, rings and sleeve work out considerably cheaper than a first oversize piston from Wossner. (PM me if you want details)
My 350, number #1, tends to burn a bit of oil on long high speed road trips, not slow pootling round the lanes. As does my 325. I have been advised to change to Motul fully synthetic 20w50 by XT600 guru David Lambeth, which is supposed to be THE THING for big bore over-square thumpers. Lyndon Poskitt also used this until he got sponsorship from Motorex... I have just done an oil change with it, but have yet to get out for a long thrash...
Thanks for your reply Mossproof. As you say, it looks like I am heading for a complete tear down......I have ordered valve seals and gaskets from Steve, so as soon as they arrive I shall be set up to have a look at that end of things. As this 350 conversion was done by Brian, I am certain it will have been run in correctly! I am aware that the owner prior to me did not use the bike much during his two year ownership; so there could be some 'lack of use' damage; but for now it's 'wait and see'.
