KM130r 4 mix. Valve damage.

[champagnecharly]

Hi,

 

Just taken a km130r apart, valve stem had snapped and dropped and jammed piston.

There is some very minor score marks inside cylinder but the rest can still see the honing pattern. Rings seem good with no marks. Piston walls are seemingly perfect. In fact it looks as though it has had very few hours.. However my concern lies (possibly through ignorance) with

 

A) Top of piston marked/ dinted. with the tiniest of chips on one of the top corners.

 

 

b) Valve Seats cylinder side seem perfect but looking underneath/ internally from where the spring sits there is nasty wear.

 

With both these issues is there any way they can effect the running of the machine. anybody think it may before I fork out for new parts?

 

I just have the piston and crank in ultrasonic cleaner to remove any swarf that may have fallen on.. after it is all cleaned up.. if I re-grease the bearings and soak in oil.. which oil should I use to let it all soak?

 

Also wondering.. why is it these valves keep breaking? So many reports of the same.

[Ray1]

Piston should be fine, its the con rod that should be the worry, ive seen many 4mixes that have dropped a valve and the con rod has slightly bent. With the valve seats you may be extremely lucky but ive only ever seen a few that are not damaged due to a dropped valve. Where the spring sits there should be no wear, unless you mean the valve guide. Post a pic. The valves keep breaking due to using wrong oil and lack of maintenance.

[champagnecharly]

Photos uploaded.

 

Con rod "appears" dead straight.

 

Where the sprin gsits.. it is damage as opposed to wear..the little washer was snapped in half and had lodged itself in there. and on the underside there is damage where I presume the bent and broken valve hit the top and jammed.

[champagnecharly]

Right well.. Having taken off the other valve off the problem is pretty darn clear that a whole section is missing the break is so clean it looks as though it's another part that is pressed in however nothing in the diagrams to say the same so looks like it's properly dead.

[champagnecharly]

Actually after cleaning it up i am sure it's another part pressed in.. It lookes like an oilite bearing bush. Anyideas if this can be sourced and fitted? Not sure where the one that was in there has gone..

Edited July 12, 2014 by champagnecharly

[Ray1]

Yes the guide is pressed in and are not available as a separate part.

[spudulike]

The piston looks OK, the valve seat may be able to be ground in, look for a nice grey seat around the full circumference when done - do the other and compare. If it isn't good, you will lose compression and burn the valve out in time - if you have time, try it.

 

I admit to hating these Stihl 4T engines and not having had many on my bench, two strokes are far simpler and have never seen valve issues with them:sneaky2:

[champagnecharly]

Ok.. well I'll give it a try.. It's dead and I'd be chuffed if i can get it working.

there is a tiny dint in the seat which I hadn't spotted until giving it a ultrasonic bath...

 

Another thing i noticed when cleaning is that on top of the caked exhaust valve, the inlet valve is the on that snapped there is a distinct blueness to the seats as though it had got to some extreme temps..

 

 

Wondering if there is any reason why not to use a standard oilite flange bearing? Its hard to measure Calipers out of battery but it seems like the guide is 3/16 x 5/16 x 1/2 which is a standard bush size... Any thoughts?

[spudulike]

Ok.. well I'll give it a try.. It's dead and I'd be chuffed if i can get it working.

there is a tiny dint in the seat which I hadn't spotted until giving it a ultrasonic bath...

 

Another thing i noticed when cleaning is that on top of the caked exhaust valve, the inlet valve is the on that snapped there is a distinct blueness to the seats as though it had got to some extreme temps..

 

 

Wondering if there is any reason why not to use a standard oilite flange bearing? Its hard to measure Calipers out of battery but it seems like the guide is 3/16 x 5/16 x 1/2 which is a standard bush size... Any thoughts?

 

Thoughts - yeah, buy a two stroke:thumbup:

 

These sort of projects can take days of work and still not work so don't go too mad, it may well be not worth it!

[GardenKit]

I'm feeling pedantic, so "skip it, and buy a Tanaka!"