Flushing oil

[Genniker]

Just at the end of a 6 month process to get a long-stood  bike back on the road; carbs, ignition, electrics, valves etc all sorted.

Thinking that some sludge might be lurking the the oil galleries and mindful of the important oil feed to the sohc, together with possible gummed  piston rings, I did wonder whether to run through a quick flushing oil cycle as part of the 'return the the road' procedure.

Never done this before, but wondered what thoughts and opinions on this may be?

[Andrew-S]

Flushed my CB750 K1 through as it hadn't been used for 3 years, used the same product I use on my TRs - I also squirted a few drops of engine oil down the bores and a few squirts on valve gear etc and let it stand for a few days and kicked it over a few times without plugs fitted before starting on the button. Then I ran the engine up to temp and drained the oil overnight (also removed the oil canister/filter), checked for any nasty stuff (like swarf or silvery shimming in the oil) and luckily there wasn't - refitted the canister/filter the topped up with flushing and ran it for a few minutes until warm then drained it again overnight, replaced the filter and topped up with oil, job done.

 https://www.ebay.co.uk/itm/SAE-20W-Flushing-Oil-4-55-Litre-Mono-Grade-Engine-Oil-4-55L-Flush-System-Carlube/302141176880?ssPageName=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649

[Genniker]

Thanks for the insight, it strikes me that there's nothing to lose from adding this extra (safeguarding) step into the process. After being stood for 30 years, one extra job doesn't strike me as being an unreasonable thing to do.

[florence]

If it has been standing that long, I would not take the risk, I would drop the engine out and strip it down and check everything.  Some of the oil ways are tiny.  That way, if there is anything that needs servicing you will be able to do it and then have full confidence in the machine.  A friend of mine ran a 550 that had been standing.  He came back from the first test ride with it smoking like a bonfire.  I stripped the top end and found all the piston rings had shattered, the longest bits being about 3cm. 

Whilst in there I would replace the timing chain and, if worn, the tensioner.  Sorry if this seems very cautious but it is expensive if it all goes wrong.

I don't know what others think?

[Andrew-S]

If it's been standing 30 years I would urge extreme caution if you plan to merely flush it trough - turning over for valves and timing is one thing, but running and riding may expose you to problems as outlined above.

[Rob62]

As well as flushing the motor, don't forget the oil tank.. there will be sludge at the bottom of the tank. Remove it and slosh a bit of petrol around a few times, also get a big pipecleaner type brush in there if you can.... Look at the rocker tops and in the sump to assess the cleanliness of the motor before you decide if it needs a strip down…. Stripping is a major job and is not always necessary depending on how clean the motor is inside. turning the motor over manually and looking for fresh oil emerging through the cam shaft feeders will also give some indication if a strip is necessary.
This is how I assessed my motor, all was looking ok so I ran it.... no rattles, no burning oil and since then no problems after 2k miles of running.

[Tomb]

Its in 500/550 section so guessing wet sump - no tank.

I've just picked up a motor that had been stood for years, looked Ok, crank turned smoothly but I didn't spin it much. Luckily someone had snapped a spark plug so I removed the head and found a valve sticking, glad the plug needing doing otherwise I would have bent a valve or worse had I spun it over.

[Rob62]

Well spotted Tomb.... i tend to get fixated on the 750. Yes regarding the stuck valve...there can always be a lurking problem on any motor.... any advice given is only general 😁

[Genniker]

It's only got 9000 miles on the clock and the oil in it is very clean, so tempted to trust that all is well within the engine.

I had intended to wipe clean all the rockers as a test to see if oil gets back to them.

Compression good, so hope rings ok.

I think that I will risk a start-up without a strip-down. I'm going to take things slowly, with no load put on the motor in the first instance.

[Rob62]

If it looks clean inside the rocker and inside the sump...and the rest of the bike suggests that the milage is accurate... and if the compression is good...and the oil light goes out quickly...chances are it will be ok. Take it slowly... 

[Trigger]

Never trust a engine that has been stood for years. The rings can be glued in there housings and it doesn't mater how much flushing you do, you will never release them. valve seats pitted from rust and a shed load of other issues 

[Rob62]

Stuck rings will surely result in low or no compression.... if so it wont run properly and will then have to be stripped. If the compression is good on all 4 cylinders i would suggest the rings are ok and its worth running... not every engine needs stripping !

[Trigger]

Such false information !
I have stripped shed loads of engines with good compression and the rings have been stuck, liners rusty. You can get good compression with carbon build up.
Compression testing is not very reliable and will show if you have a holed piston or a badly bent valve. just look a Julie's rebuild thread and the mess her pistons were in (some with no rings left, the compression test on her engine was 148 to 157 psi and started first time on the button, every time   

I have just been reminder by another member that we did a compression test on a SOHC engine some years ago, that I built with no rings on the pistons and because of the piston to bore clearances being less than a thou, we were still getting 130 to 150 psi across all four.

[royhall]

Got to ask this Graham, why did you build an engine with no rings?

[SumpMagnet]

rings rub on the barrel.....friction....saps power. Building with no rings gives less friction and more power...stands to reason. A racer told me ....... all the fast lads were doing it back in the day....


ahem....