rust in bore

[metalskin]

i took the head off for a clean, and to have a quick look at the bore.. and this is what i found inside.


and i guess this is where the rust has gone, burnt into carbon build up


cleaned up, it seems to have some stress fractures or something, couple of little chips out of it.


it runs ok but lacking in power and has other issues.. how much will that rust effect performance and reliability etc?

                                                                                                  cheers, metalskin.

[DR]

Sadly Metalskin rust is one of the most abrasive substances known. Pull the motor down now and at least get rid of all the rust in the cylinder and flush the crank with kero. Do not clean it out with petrol it is very abrasive also and combined with rust when you turn the crank it'll damage the bearings surfaces. If you leave it in there and ride as is you'll send rust all through your crank bearings, top and bottom end it will also stuff your piston and rings abd bore if it is salvagable. The 'littte stress fractures' marks/lines aren't fractures, you'll find that type of casting mark on many alloy parts It's not all bad news but clean it all out now to improve your chances. Inside of any motor should be scrupulously clean and you won't get any sort of longetivity or reliabilty at high rpm otherwise. I deal with lots of shitboxes that have sat and sat. Never ever start the engines on these bikes until you at least whip the head off to inspect the bore for rust. So many people have said oh yeah, I poured some fuel in and it started and it runs great, but, when you get it home it's basically rooted. Sometimes the best intentions lead to the biggest mistakes

[metalskin]

thanks for the diagnosis doc. if i cleaned it up i'd probably loose a bit of compression,
but would be a lot better for the engine? would a light clean up with 800 grit sandpaper be better than nothing?
or would it remove the rust but not metal leave pits and cause blow by? cheers, metalskin.

[Nathan S]

It depends on what you want from the bike.

The "right" thing to do from here, is to get a rebore - and it might take a couple of rebores to get all of the rust pits out.
You'd also thoroughly check out/clean up the crank, & conrod. The main bearings, small-end bearing, gudgeon pin and big end bearing, should be replaced if there's any sign of corrosion on them.
Then you could rest easy, knowing that the engine is without problems.

There are many other, simpler/cheaper paths to take, if you're prepared to live with a less than perfect engine.

The simplest path that I'd be happy with for myself, would be:
Check the bearings for any corrosion, or excess slop. Assuming that you find none, give everything a really good clean. Give the bore a scuff/hone. Re-assemble. Ride.

FWIW, I have an IT125 barrel with some "interesting" rust pits in it (the bike it was fitted to, was leaned up against a shed for several years, allowing moisture to get in). The barrel and piston were simply cleaned, and fitted to another bike that did a season or two of HEAVEN racing before I ended up with it. It was down on compression, but it kept on running.
Like I said, it depends on what you expect from the bike.

[metalskin]

i just want to get from a to b, without breaking down. not to worried about performance.
if i put a 175 top end on it (its a 125), can i jet up my carby and get the autolube adjusted?
trying to figure out a cheaper fix and i know i wont have much luck finding a 125 top end.
if this rust has done damage to the bottom end, could that that explain the weird vibration
that is occuring betweeen 3700 - 3900rpm? looks like im going to be chasing up a complete cheap replacement engine.

[Nathan S]

Pull the barrel, and check the big-end bearing. Any perceptible up-and-down play is really too much, although a tiny amount is OK for a non-race motor. My wife's later DT175 has a huge amount of play in the big end (like nearly 2mm up and down! ) and it ran fine - the vibrations made your hands tingle after about ten minutes, though...

If you go for a 175 top end, then make sure you get one from an early monoshock bike. The twin shock top ends are different, and the later (1985+) monoshock top ends are also different. I've probably got a spare ($0), but it will be in need of a rebore.

[k2000x]

synthetic oil does this as it is hydroscopic meaning it will draw moisture out of the air when bike is parked for a while it doesnt have any protection property for rust like good old mineral BASED OILS

[crossedup2]

Hi Metal

I'd take Doc suggestion, clean up the barrel, flush out the bottom end and re-assemble. There is a good chance the vibration is the bottom end but live with it. When it starts to sound like a bucket of bolts then do something.

In the meantime, same some money or ask on the forum for an old engine of the right vintage and build yourself a budget motor. The best part about that is you will learn heaps, there are various combinations of gear box sets and porting you could play with and we can all help. The rights parts can be found, bearings, rod kits and stuff for the right price you just have to know where to look. 

The end result may be one motor for commuting and one for playing with 

In many years you may achieve Yamie Grand Master status like Nathan S.

Peter

[metalskin]

i've pulled the top end off, cleaned it up a bit. its lightly pitted but still has good compression 
no play in the big end except less than 1mm of side to side movement. no rust on the crank. everything seems good.

there was a tiny bit of 2t oil in the bottom end, im guessing the auto 2t system lubes the bottom end as well?
havent fired it up yet but when i cleaned the carby, i had a couple of small drops of water in there, i reckon that
could have been causing it to be so temperamental. it seemed to rev out/decelerate like it should with the choke on.
cleaned the rust out of the tank as well used some CLR.. the amount of crap that came out was surely enough to cause some damage.

the oil is whatever was in it when i brought it(told it was mineral), but then again its probably the standard tt stuff like most people use

[crossedup2]

Metal

Save yourself some head aches later, put in a fuel filter ( the simple clear plastic triangle type so you can see fuel movement) . It might be a good idea not to wash your bike so often! If you do wash it then start it and ride it around the block to dry the inside and air filter out (plus what goes down the pipe!) One of the worst things a 2 stroke hates is to be left wet and unloved.

Good luck

Peter

[metalskin]

i replaced the fuel filter the day i got it. now the new prob is the bike seems to flood the crankcase or something,
like i said earlier it ran better with the choke on. now it runs fine, but if i set the idle screw it seems to take ages
to wind down unless its at a point where it wont idle when cold and dangerously low when warm. cheers, metalskin.