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Went to Tan Hill on Saturday, short ride about 80 miles. Scooter was running great and as I was riding alone got to give it a good blast. Parked up out side the pub, but when I went to start it back up half an hour later in had no compression, barely tried to fire then gave up the ghost.

The whole top end was rebuilt with new piston, all bearings and seals and new reeds around 1000 miles ago. Had no suggestion of any issues and I remember thinking how well it was running.

When I took the top end off the top ring was fully stuck in the piston and the bottom ring stuck in half way round. There does not seem to be damage to the piston causing it to nip the rings.

Before the trip I started using Exol fully synth. don't know if that is the issue, just putting it out there to see if anyone has experienced similar.

I did have problems with gumming rings, not as excessive as yours, with exol fully synthetic oil. The problem went away with another make of oil.

What % you running.........I run 2% and no problems.......

is it at all possible that the piston has struck the head where the shiny part is? and compressed the grooves.

Andyf wrote:is it at all possible that the piston has struck the head where the shiny part is? and compressed the grooves.

Thats well spotted.
Especially to the right of the plug thread and if that is the case would certainly close the ring grooves up..

Russ had the same last year twice, also using that oil. he's been ok since though as have many others in our lot use that oil.
no sticky rings using groundsman though in mine or the others in our lot using it.

Andyf wrote:is it at all possible that the piston has struck the head where the shiny part is? and compressed the grooves.

if it does hit the head, it has for the last 10 years. This is essentially the same engine I built for Holiday bin Holland 2003 and won the Coast to Coast on in 2009.

MickYork wrote:What % you running.........I run 2% and no problems.......

I run 3%

Eden wrote:Russ had the same last year twice, also using that oil. he's been ok since though as have many others in our lot use that oil.
no sticky rings using groundsman though in mine or the others in our lot using it.

I had nearly finished the second 25 ltrs of Exol fully synth though , with no previous sticking ring issues. i ran at 4% in a steel lined RB250.

On the way down to Ebensee on the A3 running fine , pulled in to the motorway services just north of Nuremberg, pulled up at the pump and it just died ? strange ? kicked it over , and no compression ??
So barrel off , new piston in , and on my way i go, on to the rally and then Czech Rep. back into Germany and back onto the A3 .
We pull into a service station and the same thing happens ??? Id done 600 miles . I didnt have another piston , so had to free the rings out of the orig piston, replaced and off we went again ??? i was on the last ltr of exol , and id bought some Rock oil Andy Francis at the rally , so started using that .
I did another 800 miles before i got home without issues .
I blew a hole in the piston on the next rally i went on and havent used the scoot since really as its still in bits
I did wonder if the Exol oil had something to do with it ? but as i said id done 50 ltrs without and similar issues ?

Here's something spooky though , when i looked at my pics and the geo tags , the second breakdown was in the exact same services ! just on the opposite side of the motorway

Nobody has given me a plausable cause really , i dont think it was the oil myself ?

carlos fandango wrote:
Here's something spooky though , when i looked at my pics and the geo tags , the second breakdown was in the exact same services ! just on the opposite side of the motorway

Spooky that Russ

If the rings free up easily then it would be a 'gumming' issue. If the piston has been hammered then you would need to take a file to the ring lands to get the rings to fit back in.

my first thought was overheated synth oil too. There are definite signs of burning oil on the head and piston.They should be a nice biscuit colour . Have you done a leak down test to eliminate a leaky oil seal ?
There is an interesting article on MB Dev site about this subject and the conclusion Mark came as I recall was the type of oil used being synthetic rather than mineral.

Shouldn't think you'd start any engine with that spark plug to be honest....

johnnyXS wrote:.... Have you done a leak down test to eliminate a leaky oil seal ?

Good point, it does look as if the head might have been leaking into one of the stud holes.

Mag wrote:

Andyf wrote:is it at all possible that the piston has struck the head where the shiny part is? and compressed the grooves.

if it does hit the head, it has for the last 10 years. This is essentially the same engine I built for Holiday bin Holland 2003 and won the Coast to Coast on in 2009.

must be the oil

Its possible the Exol has a high castor content, this will cause rings to gum up..

Bugger I started using this after rave reviews and my last 3 strip downs with stuck rings. I was on rock fully synthetic.

I used exol semi & then fully synthetic in a mugello 186.2% mix never had a problem with stuck rings,over approx 5000miles.

its not the oil that is the problem its the temperature the engine is run at that causes the oil to burn .

If you run with a lean mixture or your engine is running hotter for some reason like sustained long runs on hot days then that is when the oil can cause problems .

It would be interesting to see if anyone has done any tests using a combination of synthetic oils togetherwith petrol with additives at higher than normal temperatures. Some petrols have more additives than others.

johnnyXS wrote:its not the oil that is the problem its the temperature the engine is run at that causes the oil to burn .

If you run with a lean mixture or your engine is running hotter for some reason like sustained long runs on hot days then that is when the oil can cause problems .

I did 2 days of 230 mile German Autobahn runs in 37/38C going to the Euro using 3% Exol without issue, this is on Mugello kit with M Tech adv'/retard which helps with cooling though. Used it in all my scooters for 3/4 years now without problem.

Rich'

Rich Oswald wrote:

johnnyXS wrote:its not the oil that is the problem its the temperature the engine is run at that causes the oil to burn .

If you run with a lean mixture or your engine is running hotter for some reason like sustained long runs on hot days then that is when the oil can cause problems .

I did 2 days of 230 mile German Autobahn runs in 37/38C going to the Euro using 3% Exol without issue, this is on Mugello kit with M Tech adv'/retard which helps with cooling though. Used it in all my scooters for 3/4 years now without problem.

Rich'

Hi Rich,

I also use an Mtech, also I use an EGT to keep an eye on temperature fluctuations.