Engine wear

[user 196652]

Stihl MS250. 18 yrs old.
Can anyone tell me if the scoring on the piston and cylinder is significant enough to need replacement?
Piston ok except for this. I can just about feel it with my finger nail:



Can't feel this scoring with fingernail rest of cylinder looks ok:

 

[huskihl]

It looks like they missed the bevel on the intake floor possibly?

 

[user 196652]

It looks like they missed the bevel on the intake floor possibly?

I re-built the engine about 7 years ago and I think I saw the cylinder scoring back then so you may be right, it may have been there from the beginning. If so I don't think it has caused a problem. The piston scoring is new since the last re-build.

 

[Vintage Engine Repairs]

Clean that transfer, look for damaged or missing plating and then measure skirt to wall clearance.

 

[user 196652]

Clean that transfer, look for damaged or missing plating and then measure skirt to wall clearance.

Cleaned the cylinder. All looks ok except for a nick which I can definitely feel with finger nail. It's the one furthest back...definitely would be hitting the piston as it's right on that edge unlike the one closest. What to do with it? If it means a new cylinder I would like to get one with a decompression port which mine doesn't have as it's the typical MS250 dislocate shoulder before starting scenario.

Edit: With the rings off the piston ('cos I broke them), the feeler gauge measured .002/0.05mm between the piston and the skirt.

 

[Vintage Engine Repairs]

Looks like you’re getting there mate. Keep going with the abrasive as there is still more transfer. 240 - 400 grit and lots of elbow grease

Re that chip, I can’t really see it, but use a dremel if you have one and a diamond bit and gently smooth any high spots / burr off and you’ll be fine.

I have had far worse flaking around the ports and once you smooth it, you’ll never know.

Being a Ms250 it’s not worth spending money on oem new parts and Chinese parts won’t work as well as what you have there.

If you can manage without the decomp, do so.

I have had some horrific looking pistons and cylinders that run beautifully once you clean any damage (high spots) that can catch.

Edit: 0.05mm is very little wear. Slap becomes audible at around 0.13mm and I have come across machines with 0.3mm clearance - you’re a long way off

They slap like crazy and it’s not good, but it gives you some idea how little wear you have.

 

[user 196652]

Looks like you’re getting there mate. Keep going with the abrasive as there is still more transfer. 240 - 400 grit and lots of elbow grease

Re that chip, I can’t really see it, but use a dremel if you have one and a diamond bit and gently smooth any high spots / burr off and you’ll be fine.

I have had far worse flaking around the ports and once you smooth it, you’ll never know.

Being a Ms250 it’s not worth spending money on oem new parts and Chinese parts won’t work as well as what you have there.

If you can manage without the decomp, do so.

I have had some horrific looking pistons and cylinders that run beautifully once you clean any damage (high spots) that can catch.

I nearly used the word Dremel but thought better of it in case it was a big no no.
Not used any abrasive so far, just a good couple of soakings with the Yamalube cleaner.
Thinking I will go with the Yamabond 4 sealant (sets in one hour) rather than the Dirko (24hrs to set). I have an opened tube of Dirko from 7 yrs ago but I guess that will be no use by now?

 

[Vintage Engine Repairs]

I nearly used the word Dremel but thought better of it in case it was a big no no.
Not used any abrasive so far, just a good couple of soakings with the Yamalube cleaner.
Thinking I will go with the Yamabond 4 sealant (sets in one hour) rather than the Dirko (24hrs to set). I have an opened tube of Dirko from 7 yrs ago but I guess that will be no use by now?

I edited my post to give you an idea on how bad piston slap can get

Gotcha, yeah use some abrasives in there - you may find that the abrasive paper will knock the high spots off that chip

Re sealants, Dirko is by far the best in my experience, but I use Yamabond 4 too sometimes. Both should get 24 hours cure time otherwise they tend to absorb the fuel and swell.

Yamabond 4 is the exact same products as Threebond 1215 (Threebond make Yamabond) a heap cheaper for a lot more, even from Repco!

That Dirko you have will be well and truly set in the tube it’s been opened and just closed with the cap.

Stihl don’t sell Dirko any more, if you buy it, you’ll be handed Pactan. I haven’t tried it, but if it’s good enough for Boeing, it will be fine for a clam shell

 

[user 196652]

Looks like you’re getting there mate. Keep going with the abrasive as there is still more transfer. 240 - 400 grit and lots of elbow grease

Re that chip, I can’t really see it, but use a dremel if you have one and a diamond bit and gently smooth any high spots / burr off and you’ll be fine.

I have had far worse flaking around the ports and once you smooth it, you’ll never know.

Being a Ms250 it’s not worth spending money on oem new parts and Chinese parts won’t work as well as what you have there.

If you can manage without the decomp, do so.

I have had some horrific looking pistons and cylinders that run beautifully once you clean any damage (high spots) that can catch.

Edit: 0.05mm is very little wear. Slap becomes audible at around 0.13mm and I have come across machines with 0.3mm clearance - you’re a long way off

They slap like crazy and it’s not good, but it gives you some idea how little wear you have.

Can I use wire wool? 'cos I like using wire wool on stuff.
Just opened the Dirko, hasn't hardened at all even at the top but I reckon it might not set.

 

[Vintage Engine Repairs]

When you say transfer do you mean carbon in the exhaust port or the lines of residue on the walls of the cylinder itself?
Can I use wire wool? 'cos I like using wire wool on stuff.
Just opened the Dirko, hasn't hardened at all even at the top but I reckon it might not set.

That’s crazy you have had an opened tube of Dirko for 7 years and it’s not set!

You can use whatever you like really, grab Yamabond or 1215 from repco. All 3 work

 

[user 196652]

That’s crazy you have had an opened tube of Dirko for 7 years and it’s not set!

You can use whatever you like really, grab Yamabond or 1215 from repco. All 3 work

All nicks, dings, scratches, carbon, transfer and Dirko removed......you could eat yer dinner off this engine now
Amazingly the bit of Dirko I took out of the top of the tube has hardened on the bench!
Just have to wait on new seals and rings, not in stock with dealer.

 

[Vintage Engine Repairs]

Great I look forward to seeing it run.

 

[user 196652]

Great I look forward to seeing it run.

Just figuring out how to get some oil in there for the first start 'cos apparently that's when a lot of wear can happen after a re-build. I was going to slather everything with neat oil before assembling but I don't want to risk it interfering with the sealant as it sets. I think I might use a syringe with oil through the ports after the sealant has well and truly set. Is that how you do it?

 

[Vintage Engine Repairs]

Just figuring out how to get some oil in there for the first start 'cos apparently that's when a lot of wear can happen after a re-build. I was going to slather everything with neat oil before assembling but I don't want to risk it interfering with the sealant as it sets. I think I might use a syringe with oil through the ports after the sealant has well and truly set. Is that how you do it?

Don’t over think it, a smear on the cylinder walls, piston and bearings, then go over the surfaces that are to be sealed with acetone, then apply a small amount of Dirko to both surfaces Iincluding seals and the pockets and quickly bring it all together and into the case. You have about 7-10 mins max of work time with Dirko (rather than an hour or so with Yamabond 4) so don’t dillydally!

 

[user 196652]

Don’t over think it, a smear on the cylinder walls, piston and bearings, then go over the surfaces that are to be sealed with acetone, then apply a small amount of Dirko to both surfaces Iincluding seals and the pockets and quickly bring it all together and into the case. You have about 7-10 mins max of work time with Dirko (rather than an hour or so with Yamabond 4) so don’t dillydally!

I forked out the $27 for a tube of Pactan 'cos I just wasn't sure if the old Dirko would hold up and your double blind study comparing sealants had me convinced on the Dirko. I think the Pactan is likely to be a very close match. Patent held by Boeing, made by Tremco. Couldn't find an msds for the Pactan to compare it with the Dirko. Overthinking it......moi?

 

[Vintage Engine Repairs]

I forked out the $27 for a tube of Pactan 'cos I just wasn't sure if the old Dirko would hold up and your double blind study comparing sealants had me convinced on the Dirko. I think the Pactan is likely to be a very close match. Patent held by Boeing, made by Tremco. Couldn't find an msds for the Pactan to compare it with the Dirko. Overthinking it......moi?

Yeah over thinking, I use to, too. The only 2 known sealants I’d stay away from are motoseal which has a habit of never curing and is not a gap filler (necessary for clammys) and 515 / 518 by Henkel, not gap sealers and don’t always set.
Hondabond 4, Yamabond 4, threebond 1215, Pactan, Dirko HT Red etc all work fine.

 

[Mad Professor]

Just figuring out how to get some oil in there for the first start 'cos apparently that's when a lot of wear can happen after a re-build. I was going to slather everything with neat oil before assembling but I don't want to risk it interfering with the sealant as it sets. I think I might use a syringe with oil through the ports after the sealant has well and truly set. Is that how you do it?

If you flush out the bottom end with some mix that will lube up everything, and clean it out too before initial start up. That is all the lube they ever run on.

I like seafood, but not clamshells,...........non-clam engines always get the bearings, pin, and P/C oiled up with mix oil on a rebuild.

 

[Mad Professor]

Looks like you’re getting there mate. Keep going with the abrasive as there is still more transfer. 240 - 400 grit and lots of elbow grease

Re that chip, I can’t really see it, but use a dremel if you have one and a diamond bit and gently smooth any high spots / burr off and you’ll be fine.

I have had far worse flaking around the ports and once you smooth it, you’ll never know.

Being a Ms250 it’s not worth spending money on oem new parts and Chinese parts won’t work as well as what you have there.

If you can manage without the decomp, do so.

I have had some horrific looking pistons and cylinders that run beautifully once you clean any damage (high spots) that can catch.

Edit: 0.05mm is very little wear. Slap becomes audible at around 0.13mm and I have come across machines with 0.3mm clearance - you’re a long way off

They slap like crazy and it’s not good, but it gives you some idea how little wear you have.

Nice video Tom.

The audio of the piston slap brought back memories to when I worked at a Honda/Suzuki dealership many years ago. People would bring in dirt bikes still running pretty good, but really noisy. "What do you think is making that noise?" they would ask. Piston is wore out......"Can't you just put a set of rings in it?".......Can't say how long that will last you.

The bigger 250-500cc bikes made a horrible noise. Little one not so much more like a saw does.

We used to tear down bikes and intake skirt of piston would be worn obviously thin. Some had bridged intake ports, and pistons had a grove worn into them from the bridge. Others waited until the skirt broke off and it seized. This was 1970s and many of the bikes still used cast iron cyl liners, and you could save cylinder with an overbore.

 

[user 196652]

Now that my chainsaw is back from the laundry, I have been getting rid of the last of the crud with some ear buds, which got me to wondering if I should give the chain brake mechanism some grease?
Also, whilst on the subject, but not wanting to be controversial..... should I grease the clutch needle bearing too?

 

[Vintage Engine Repairs]

You can put a small amount of grease on the pins, a tiny drop of oil on the contact anreas and then a quick spray over the whole assembly with a rust preventative - INOX mx3 is excellent.