Jonsered 670 W Piston/Cylinder Question - Is it Toast?

[Alphadelta]

Okay! It looks worse than it feels. Older 670 W that I got before it got thrown in the scrap bin. Used to be an old fire department saw. It ran then suddenly just stopped. I pulled the cylinder and piston and was greeted with this on the exhaust side. My first thought was welp, there goes those two, but they don't feel rough. I can catch my finger on one spot on the piston and the cylinder is marked but doesn't feel like anything. The reason I think it stopped was the large metal washer that sits in front of the pump got caught on the sprocket.

I have found one replacement part for this but OEM is not an option. I am still trying to learn the line between "it's toast" and "scotch bright and put it back together".

If it matters, prior to this I sat and ran it for 5ish minutes and it had great compression and purred like a kitten.

As always thanks for any insight you may have.

 

[Alphadelta]

Well, I think I was crazy if I thought the piston was reusable. Cleaned it up a little and the scoring is defiantly there, but only on the exhaust side.

 

[pioneerguy600]

That cylinder will clean up nicely, find a NOS piston or a Meteor replacement, there will be a lot of hours run time left in that set.

 

[Bob Hedgecutter]

Saws do not generally end up in, or near to, trash piles for no good reason.
I find it hard to believe in that condition it was blowing near 200psi compression and running it before a thorough investigation when you had already seen the scored piston was perhaps not the wisest decision.

Clean all transfer/carbon out of cylinder- new piston and ring, check the big end bearing and main crank bearing meticulously. Put it back together and do a full pressure and vac test before turning a new piston into a same looking piston.
Any scored piston requires finding out how it came to be that way and repairing it- or you end up doing it nice because you do it twice.

 

[pioneerguy600]

Saws do not generally end up in, or near to, trash piles for no good reason.
I find it hard to believe in that condition it was blowing near 200psi compression and running it before a thorough investigation when you had already seen the scored piston was perhaps not the wisest decision.

Clean all transfer/carbon out of cylinder- new piston and ring, check the big end bearing and main crank bearing meticulously. Put it back together and do a full pressure and vac test before turning a new piston into a same looking piston.
Any scored piston requires finding out how it came to be that way and repairing it- or you end up doing it nice because you do it twice.

 

[Maintenance supervisor]

Piston done, cylinder maybe salvageable.

 

[Alphadelta]

That cylinder will clean up nicely, find a NOS piston or a Meteor replacement, there will be a lot of hours run time left in that set.

Thanks, I found the meteor piston and ring off of Baileys so that's on order. I am going to seek out an OEM used cylinder off the trading post too. Have you found a method to clean up cylinders that works well?

 

[Alphadelta]

Saws do not generally end up in, or near to, trash piles for no good reason.
I find it hard to believe in that condition it was blowing near 200psi compression and running it before a thorough investigation when you had already seen the scored piston was perhaps not the wisest decision.

Clean all transfer/carbon out of cylinder- new piston and ring, check the big end bearing and main crank bearing meticulously. Put it back together and do a full pressure and vac test before turning a new piston into a same looking piston.
Any scored piston requires finding out how it came to be that way and repairing it- or you end up doing it nice because you do it twice.

I am not sure if the cylinder was scored when I first ran it. Looking back the smart thing may have been to check everything before running it but I wanted to see if it ran first. Started it - let it warm up for 20-30 seconds and then ran it for about 10 seconds before it stopped dead in its tracks. I had a feeling I nuked it because just by ear it sounded off. Now I realize it either had an air leak or the carb was set too lean.

Still trying to learn diagnostics, my assessment off compression was just by feel and comparison to a Jonsered 2171 I have.

As for the bottom end that is exactly what I did, the bearings and crank feel good. I appreciate the feedback. I am just happy I didn't toast the whole saw.

 

[RedneckChainsawRepair]

Cylinder will clean up IMO.

Here is a Dukes 268xp piston kit I got from Chris at sawsalvage in my 670 champ.

Moly coated that I am really surprised hasnt come off already. Most dont last a few tanks.

But there it is. Stock as it can be.

Make sure you get a windowed piston for your closed port saw. Lot of folks will try and sell you a open port piston for it.

 

[RedneckChainsawRepair]

Before and after on my cylinder.

Easy as 1 2 3.

1 Flapper is what I do for removal of transfer. 2 by hand to make sure all gone with emery clothe. 3 is not needed but I been doing it since the first 166 race saw I redone and seen a difference. Fresh quick crosshatching.

 

[pioneerguy600]

Thanks, I found the meteor piston and ring off of Baileys so that's on order. I am going to seek out an OEM used cylinder off the trading post too. Have you found a method to clean up cylinders that works well?

Yes, we all have our own specialties we like over others, likely just personal preference. I have used the sandpaper and flap wheel method for over 50 years and it does a fine job without and accidental damage like acid can inflict.Works for me and many others .

 

[Gord404]

might as well order 2 sets of seals and an O ring that goes around your oil pump given the age of that saw- why 2 because you might screw one up putting it in and a new st of manifold gaskets- stay away from the china ones - green is best..

 

[Husky77]

Good luck with your project, you'll be suprised how tough these saws are and what you can get away with, but you have to know what your doing .
It's highly likely been abused all its life from new with flat out cold starts just from the working environment. Flat out from cold is not good as we all should know, and it probably got binned when it was getting difficult to start, they need it running to max within a few pulls when lives depend on it. It's a disposable tool that gets replaced, lucky for you. Now all it needs is some TLC

 

[huskydave]

Yes, we all have our own specialties we like over others, likely just personal preference. I have used the sandpaper and flap wheel method for over 50 years and it does a fine job without any accidental damage like acid can inflict.Works for me and many others .

Improvise, adapt, overcome.

 

[Alphadelta]

Yes, we all have our own specialties we like over others, likely just personal preference. I have used the sandpaper and flap wheel method for over 50 years and it does a fine job without and accidental damage like acid can inflict.Works for me and many others .

Awesome good to know, I will go that route. I got the meteor piston, just need to source some gaskets/seals.

Thanks for your insight I appreciate it.

 

[Alphadelta]

Good luck with your project, you'll be suprised how tough these saws are and what you can get away with, but you have to know what your doing .
It's highly likely been abused all its life from new with flat out cold starts just from the working environment. Flat out from cold is not good as we all should know, and it probably got binned when it was getting difficult to start, they need it running to max within a few pulls when lives depend on it. It's a disposable tool that gets replaced, lucky for you. Now all it needs is some TLC

Thanks . It's not my first FD rebuild. But you're right we run our saws hard when actually on scene. My department runs all Stihl 500i now except on our wildland rigs. Those 500i are impressive saws but these old Jonsered seem to be pretty bullet proof with some elbow grease.

 

[Alphadelta]

Well boys, I think this may be a bit past sanding. I have been doing some light sanding for about an hour and 97% of it looks great but one spot.

I am torn at what to do. The red is a single longer score that you can easily catch with your nail and the blue is just a rough spot that I think may come out with some elbow grease.

My thought process is maybe one of those small engines hones and see if it makes it passable and if not scrap it.

Thoughts?

 

[huskydave]

I think your going to have to take 20 thousandths off just to blend that one groove in. I would personally source another jug.

 

[Alphadelta]

I think your going to have to take 20 thousandths off just to blend that one groove in. I would personally source another jug.

Yeah I may have found someone with an OEM.

Outside of buying a very expensive one from a parts supplier my other two options are Chinese or Lil Red Barn has a kit but they don’t say who makes them.

I think it would run with a new piston and ring but this is a build for a friend. So goal is to just do it right the first time.

 

[huskydave]

check out this kit on ebay, 52mm Bore Nikasil Cylinder Kit Fit Jonsered 630 670 625 Chainsaw. It might be worth looking at. $75 US, it comes with a clutch cylinder piston crank bearings seals filters new oil pump. I wouldn't use the fuel line or the ignition switch but the rest of it may be good enough. If you go that route use the original oem piston circlips.