Seized engine - non permanent. Maybe cylinder glaze/varnish?

[bikerpet]

I went to start my '21 TRS RR 300 (120 hours engine time) today and found it was jammed.
Weird, as it was running fine yesterday right up until I stopped it and put it away.
I'd just checked the coolant the day before and it was still correct level so I was comfortable it hadn't cooked from lack of water. I also knew 100% that I had oil in the fuel - 140ml to 13L as I've used all along.
I had heard a slight and intermittent rattle for about the first minute while it warmed up, but couldn't identify where it came from. I tried the screwdriver to the ear trick over parts of the engine and it didn't sound like it was coming from anything I listened to.

I pulled off the clutch side and could find nothing wrong there. The clutch basket rotated freely on the tiny bit of play in the primary gears, so it wasn't the clutch or starter gears, and the gearbox moved fine when I pulled the clutch so it wasn't that.
Took off the magneto cover and there was absolutely zero movement on the flywheel. So I figured it was crank or piston.

Pulled off the head and there was a lot of glaze/varnish - not sure the correct term for burnt on oil? Hmmm.
I decided to put a socket on the crankshaft and see if some judicious force would move it. It broke free reasonably easily so I moved it to bottom of stroke.

Looking at the circumferential lines I'm thinking maybe the varnish hardened up when the bike cooled and stuck the rings to the barrel?

I got in there with a plastic scraper and cleaned a fair bit up, then more with a Scotchbrite and some contact cleaner. It came up virtually good as new, not a scratch in sight and nice OEM hone marks. Hooray.
Also cleaned the carbon out of the head and piston top. Nice and shiny again.

Put it all back together and it started and ran as well as ever. Phew.
It had the same rattle for a couple of seconds after it started, but then gone. I'm tending to think it sounds more like something external than internal, but that wouldn't go away as the engine warmed up. Odd. I'll do more investigation when I hear it next, if I do. I'm a little nervous about that.
I'll probably pull the barrel off and give the piston and rings a clean once I've ordered a gasket & O-rings - I've got a trial tomorrow so wanted it back together.

So I'm wondering a couple of things:

1. I've been using Putoline Trial, which I've previously done hundreds of hours on in Beta's with no issues. But now I'm wondering if Putoline is known for gumming up the works?
2. Is this a "thing"? That rings stick to the build up in the cylinder when it cools. Or should I be looking deeper for a more significant cause?

I wish I'd taken a photo before reassembling, it looked vastly better than this!

Thanks for any enlightening comments.

Edited August 5, 2023 by bikerpet

[lemur]

Yikes that is not a pretty sight.  The only time I had a 2-stroke look like that and have rings jam was in a chainsaw that I was using old 2-stroke oil that was so old I should have discarded it.  I had to remove the piston and clean behind the rings, no way you could free up the rings proper without removing the piston.

[lemur]

I just googled that oil, it's strawberry scented 🙄 why would anybody ever intentionally put something like that into an engine is beyond me.  Not much doubt you should change oil brands.   What does your exhaust packing look like, is that all gummed up with strawberry stuff too?  

What fuel are you using?  I run 50% premium pump gas and 50% Sunoco GT260 race with Amsoil Sabre 100:1 being my preferred oil.  Some brands I have tried in the past gummed up the exhaust packing real bad.

[bikerpet]

27 minutes ago, lemur said:

I just googled that oil, it's strawberry scented 🙄 why would anybody ever intentionally put something like that into an engine is beyond me.  Not much doubt you should change oil brands.   What does your exhaust packing look like, is that all gummed up with strawberry stuff too?  

What fuel are you using?  I run 50% premium pump gas and 50% Sunoco GT260 race with Amsoil Sabre 100:1 being my preferred oil.  Some brands I have tried in the past gummed up the exhaust packing real bad.

I reckon they all put something so they smell other than burning oil - they've all got distinctive smells, just that Putoline try to market theirs.
In Australia so our fuel is different to yours, but 95 octane bowser petrol. What nearly everyone here uses. Some people use 98 octane, but weirdly that often doesn't run as well as the standard 95.

Exhaust packing seems pretty good - I had it out just a few weeks ago when I belted the exhaust cap off.

[trapezeartist]

+1 for taking off the barrel and piston after your trial today. Hopefully you won't have the bore back in that state again after a small amount of running. I think you'll probably have to clean the piston rings and ring grooves as they are likely to have more of the gunk you found on the bore. Assuming the bore and piston top look clean, I'd put it all back and ride it, but whip the head off after a few more trials to check how things are evolving.

While you have the top end apart, check the small end bearing and the up/down clearance of the rings in their grooves. There's maybe an outside chance that the source of your rattle is somewhere there.

[feetupfun]

The rings stick in their grooves due to gum which is made of partially-burned two stroke oil. The rings then don't seal against the bore which causes lots of ring blow-by. The blow-by then forms a gum on the bore. When the gum cools it gets even stickier. All standard stuff for a two stroke that uses modern low smoke premix oil and doesn't get ridden hard enough to burn the oil fully.

Either use oil that burns better or ride it hard once in a while or pull it apart and clean it out more frequently.

 

[arnoux]

Take the header pipe off and just check the rings and piston skirt through the exhaust port as you rotate the engine. Also make sure the fan is coming on when it should. You can have plenty of coolant but if it gets hot and the fan is not working it will go lean and you could head towards a bind up situation. And I would definitely be swapping oil brands that looks manky!

[bikerpet]

20 minutes ago, arnoux said:

Take the header pipe off and just check the rings and piston skirt through the exhaust port as you rotate the engine. Also make sure the fan is coming on when it should. You can have plenty of coolant but if it gets hot and the fan is not working it will go lean and you could head towards a bind up situation. And I would definitely be swapping oil brands that looks manky!

Thanks Paul. I was going to give you a call.

Fan's working fine.

The skirt looked OK. Quite a bit of brown muck between the rings though.

I'll order the gasket kit from you & then pull the cylinder off so I can clean piston & rings properly.

[dan williams]

Wow! That looks like you messed up and double oiled your fuel. 

[bikerpet]

31 minutes ago, dan williams said:

Wow! That looks like you messed up and double oiled your fuel. 

Looks like it, but not. 100% confident that hasn't happened.

15 hours ago, feetupfun said:

The rings stick in their grooves due to gum which is made of partially-burned two stroke oil. The rings then don't seal against the bore which causes lots of ring blow-by. The blow-by then forms a gum on the bore. When the gum cools it gets even stickier. All standard stuff for a two stroke that uses modern low smoke premix oil and doesn't get ridden hard enough to burn the oil fully.

Either use oil that burns better or ride it hard once in a while or pull it apart and clean it out more frequently.

 

That sounds logical to me. Under that scenario the Putoline may not be a cause. It could be that given the quantity of oil in the exhaust when I got it, the rings stuck quite early due to excessive oil, then the Putoline goo was a consequence not a cause.

Or the Putoline could be crappy.

Or I just might need to go for a solid blast from time to time to keep things clean. That seems a bit odd - my riding spots are several km apart on hilly forestry road so it gets a reasonable run most days. But I just tootle along usually, maybe more speed required.

[bikerpet]

Being someone who believes in going to the source wherever possible, I emailed Putoline about this and today heard back from them.

Quote

Really thanks for sharing this image and question by E-mail.

 

For a 2-stroke engine, the riding conditions of a trial bike are actually some of the toughest out there. A low load, a lot of idling and excessive water cooling ensure that the operating temperature is actually much too low to have a good combustion process. Due to the incomplete combustion of the petrol-2-stroke oil mixture, (hard and soft) carbon deposits are formed over time. These deposits can eventually cause piston rings, exhaust ports and the piston to seize.

 

Also due to the use of the best 2-stroke oils, this can hardly be prevented over a longer period, in this case 130 hours of Trial use. There is simply not enough heat in the cylinder to allow the (oil) combustion residues to burn completely.

 

There are a number of solutions to prevent what you have shown as much as possible.

 

1) However, regularly put a lot of strain on the engine so that it can burn clean internally.

2) The oil mixing ratio needs to be adjusted slightly 130 ml 2-stroke oil on 13 liters of petrol is a mixing ratio that still functions well in practice. However, with a higher proportion of substantial taxation, this may be too little and this really depends on the degree of taxation.

3) Switching to a fully synthetic Putoline product such as Putoline MX7 or Putoline MX9.

4) Preventively after, for example, 100 hours, remove the cylinder head and cylinder for a complete cleaning.

I asked if he had a preference for MX7 or MX9 in this case:

Quote

The Putoline product TT Trial Pro is in most cases just fine, but there are always exceptions of course. The Trial market is relatively small and we have opted for a good product that we can offer at a reasonable price. That is always a compromise, of course. Offering a fully synthetic (more expensive) product under the Trial label would not be commercially interesting enough. The MX market is much larger in terms of volume and we offer a wider range of products there, because that is commercially interesting in terms of volume.

 

Even at lower operating temperatures, a fully synthetic product burns more completely in our experience and it is therefore expected that this product better suits your conditions of use and keeps the combustion chamber, piston and piston rings cleaner.

 

With our product range Putoline MX5, MX7 & MX9 we use the quality strategy: Good, better, best. The Putoline MX9 product therefore represents the latest state of the art in terms of product performance & additive technology.

The TT Trial Pro is labelled "synthetic", but I guess that really interprets as "semi-synthetic" rather than "fully synthetic". I'd assumed it was synthetic as in "fully".

So I guess I'll try the MX9.
I get a good price on Penrite (Australian brand) from my local distributor who I try to support wherever I can, he also sells Putoline so it might come down to Putoline vs Penrite price. I'm sure there's differences in the full synthetic 2T oil offerings, but I'm also pretty sure that I couldn't pick the difference based on the marketing guff.
Anyone want some discount TT Trial Pro? 😄

[faussy]

Ive never used fully synthetic oil in a trials bike because these are usually designed for motocross and more likely to do what has happened to your bike. Im guessing thats what mx stands for in the suggested oils . For this reason ive always stuck with semi synthetic. I run 60:1 and have never experienced carbon build up like this

Are you sure your bike is carburetted properly?

Edited August 7, 2023 by faussy

[bikerpet]

48 minutes ago, faussy said:

Ive never used fully synthetic oil in a trials bike because these are usually designed for motocross and more likely to do what has happened to your bike. Im guessing thats what mx stands for in the suggested oils . For this reason ive always stuck with semi synthetic. I run 60:1 and have never experienced carbon build up like this

Are you sure your bike is carburetted properly?

GG recommend GRO Performance 2t. Fully synthetic.
Beta & Sherco recommend Motul 800. Fully synthetic.
TRS show Nils Duo Synt S. Fully synthetic.
Putoline technical support manager advises fully synthetic.

I'm going to take the hint.

[lemur]

 

" The oil mixing ratio needs to be adjusted slightly 130 ml 2-stroke oil on 13 liters of petrol is a mixing ratio that still functions well in practice. However, with a higher proportion of substantial taxation, this may be too little and this really depends on the degree of taxation."

They are confirming you should run 100:1 ratio same as your service manual says. ... for what it's worth I run my TRS 300RR at 100:1 like the manual calls for and it hasn't seized up yet with more hours then you have on yours.

That crap about higher taxation is to cover their butt, in the event of a failure they want it to be your failure.  Lots of producers have taken to not even suggesting an oil mix ratio on their packaging, so if in doubt buy one that states it can be run at 100:1 on their documentation or packaging.  That's what Amsoil says right on their plastic bottle "100:1 pre mix"

 

 

[lemur]

" thinking maybe the varnish hardened up when the bike cooled and stuck the rings to the barrel?"

The rings jam up in the piston grooves and then the ring no longer follows the shape of the barrel.  That creates a gap between the ring and the barrel where raw fuel and raw oil burns and contributes to more carbon buildup.  Carbon is black and that mixes with non-combusted oil to make a glue like residue.  

A piston and its ring pack needs to operate as an assembly where gasses from compression push the ring more tightly against the cylinder barrel.  Look at how a Dykes piston ring works for a better explanation.