CBR600 Burning oil, different rates in different circumstanc

[Nipedley]

Hi guys,

My CBR600F (1988) is burning oil, this has been confusing me for a while because I'll do 100 miles and it's fine, then I'll do 60 miles and it's gone

I decided to start doing a near daily oil check and recording it against the mileage nad I think I've discovered it, I did 75 miles of short trips (between 5 and 20 miles at a time) and the oil went from .8 of max on the dipstick to .7, I was quite happy with that.

Then yesterday I did 80 miles in one go, 40 up and 40 back, and the oil is gone, maybe 2 bars below minimum on the dipstick

Does this give anyone more experienced with engines than me an idea of what may be wrong here?

Thanks for any suggestions

[Robby]

It sounds like its burning oil when it gets warm. On short runs the oil isn't getting up to temp, on long runs it is. Oil gets thinner as it gets warmer.

It shouldn't be burning much oil at all, so you have a problem. The potential solutions are:

1. Ignore it and keep topping it up.
2. Switch to a thicker oil (20W50 instead of 10W40). Only masks the problem but it may burn less oil.
3. Fix it. Could be a blocked crankcase breather (easy), could be worn valve steam seals or piston rings. Either will require stripping the top end of the engine down and spending some money.
4. Fit a used engine off ebay. Unlikely to have the same problems, these engines don't have a reputation for burning oil.

It's a cheap old bike. Engines aren't expensive or hard to change. I would be inclined to use cheap 20W50 and keep topping it up until the engine fails, then decide if you're going to replace the engine or just get rid of it.

[Nipedley]

Thanks for the reply

The last time I had the bike apart I noticed there was a small amount of oil in the airbox where it connects to the top of the engine, which I think is the crankcase breather? In which case I think that's probably fine

I will have a go with some 20w50 and see what happens, to be honest I don't think it's worth spending money on this engine, it's a 40k but already had a new clutch a few months back so I think it has had a hard life. So some 20w50 and see how we go, and then a engine with low mileage off ebay may be the route to go

Thanks for the suggestions

[Nipedley]

Forgot to mention -
I'd been riding and topping up for the last 5 months or so without thought because the bike had an oil leak from the water pump, it was only when I fixed the leak (about a month and a half ago) and noticed the oil was still dropping that I got concerned

The bike doesn't smoke at all, but perhaps that's because I've only seen it running when cold and it's not burning the oil then :/

I'll see what happens with the 20w50 and if needs be I'll grab another engine off eBay..

[kramdra]

Nope I would keep using 10w/40 thats what it is designed for. Keep it topped up and she will last a long time. Thicker oil did not work for me.

My first car had fairly major oil burning issues. 1 litre per 200 miles. To burn this much indicates a stuck oil scraper ring on one piston, compression rings are likely to be fine.

If you pull sparkplugs, deposits of carbon indicate the bad pot.

Mine was significantly worse at high rpm under hard acceleration - there were certain bits of road where I could see clouds of smoke Its likely to only burn when under load rather than revving stationary. Find a clear bit of road and study your mirrors.

[Nipedley]

Thanks for the replies guys. I was talking to a mechanic yesterday who seemed to think there should be a Gearbox breather on my bike, that on a long run the gearbox is getting pressurised and the oil is getting pushed out of the breather pipe connected to the airbox instead

However, I've studied the schematics and my engine and can't see any kind of gearbox breather, it's a CBR600F Hurricane / F1 engine (1987-1990)

The rear of the engine just has crankcase bolts, starter motor mounts, cam chain tensioner and coolant pipes as far as I can see, here's a CMSNL schematic of the crankcases https://www.cmsnl.com/honda-cbr600f-1989-englandmkh_model2233/partslist/E__1300.html#results



Any ideas or am I SOL and it's still new engine time?

[Robby]

The engine and gearbox share the same crankcases, so you only need one breather. Probably goes from somewhere on top of the gearbox into the airbox.

Disconnect it from the airbox and start the bike. If there is some air pulsing out of it, it works and isn't a problem. If there is no activity when you put your thumb over it, take it off and blow down it or poke something down.

Assuming the breather is ok, your problem is elsewhere.