350 rebuild

[bigtuna]

Well the 350 i picked up suffered the ol muffler leak. Tried to clean up the transfer but im still hanging my nail more than once, was origionally going to use 353piston in orig. Cyl. W/base gasket delete, but now ill have to use the aft. Mkt. Cul. Ill keep working on the orig. Cyl. Ill keep it and just keep sanding 800 grt. Still has the plastic clamp im surprised it wasnt leaking from the intake, but that side of pist, cyl is clean, im putting steel clamp back on. We will see how she goes. Otherwise the saw is pretty damn clean, non primer bulb saw.

 

[bigtuna]

Looks like the ring was mented into the pist on the exhaust side,

 

[irhunter]

800 grit? Is that what you started with?

Roy

 

[Bob Hedgecutter]

So did you pressure test to confirm no leak on the intake side?
Air leaks do not burn up the area of the piston the leak is associated with- like failed ignition side oil seal does not burn up the left hand side only- an air leak/lean condition burns up the hot (exhaust) side of the piston regardless of the location or cause.

 

[Bob Hedgecutter]

350's have known areas of concern.
Mufflers come loose and drop onto the top of the oil tank melting the plastic case- cure, cut down 346XP front muffler support bracket.

Loose clamshell bolts.

Plastic intake clamp failure.

Impulse line splits.

Warped cylinder risers.

You have to discover what caused the lean condition and repair that before bolting up a new top end or refurbished top end- or it will happen again.

 

[bigtuna]

Did not pressure test, top of case next to muff started melting, black exhaust marks through th back side of muffler gasket.

 

[bigtuna]

Can i add a bit of high temp rtv to the muffler gasket. Its leaking like a siv there, or just overtighten

 

[Bob Hedgecutter]

Did not pressure test, top of case next to muff started melting, black exhaust marks through th back side of muffler gasket.

Yep a loose muffler will do that- but it wont make the saw run lean.
If you can stand the noise- you can run a saw without a muffler and not harm the piston.

 

[Bob Hedgecutter]

Can i add a bit of high temp rtv to the muffler gasket. Its leaking like a siv there, or just overtighten

RTV will not work- nor help you.
There was a part available for later models that cup supported the muffler from the rear- or use an aftermarket 346XP front support bracket with the starter side leg cut off of it.
High temp loctite apparently works on the bar studs- but will be fun to remove next time you want in.

 

[bigtuna]

The bracket doesnt keep it from lesking at the gasket. It keeps it from falling off, i know anout known pronlems on the 350, plastic clamp, mufflrr nolts loosen up, yada yada yada, what other signs of seal failure any ideas, ill ord new gasket for the muff

 

[Bob Hedgecutter]

Oh well, if you know all the known faults- you will know how to fix them.
Best of luck on your adventures.

 

[bigtuna]

Lol.. this place hasnt changed a bit in the 15 yrs or so i been hangin out here.

 

[J D]

Yup, same as its been for as long as I've been here... questions are asked, good helpful advice from knowledgeable persons is given, advice is poorly recieved, thread goes downhill.
My suggestion is to take Bob's advice & vac/pressure test it as that damage was most likely caused by an air leak. Doing so will confirm the state of your seals & you can do it with just the cylinder bolted up, don't even need to put the piston in.
As Roy was eluding to, you won't get very far with just 800 grit sandpaper on transfer... start about 4x courser & finish with a scotchbrite in a mandrel. Flappy sandpaper wheels work well too

 

[bigtuna]

Thank you bob, jd ill see about getting it pressure tested, when i get it together, muffler was tight as dicks hat band when i got it, and was leaking, new gasket hopefully helps, not wanting any more case meltdown, cant find any threads about the 350's bottom end failures?? Im sure there out there, a sheet ton of the intake boot, loose muffler. And once again, thank you for advice.

 

[David Ellis]

I look forward to reading the discovery process on this project.

I recently rebuilt 2 350s that were non running. Fortunately, neither had scoring. One of the saws had missing & loose bolts "holding" the cylinder to the base block. The other had a VERY clogged air filter. Both had low compression and received new meteor flat top pistons and moto seal instead of a base gasket. I ported the mufflers too. After several heat cycles and tanks of fuel I THINK the bolts will no longer vibrate loose. They are dandy performing saws.

Good luck with your discover and please let use know what you learn.

 

[J D]

They don't tend to suffer "bottom end" failures as such. The most common significant issues (user aside) are muffler bolts & air leaks. Leaks tend to occur around the bottom end when the bolts between the clamshell & the riser come loose. I've had several of these that were a real PITA to get to seal around the bottom end which, in hind site, I suspect would've been due to a warped riser. The important thing to take away from this is:
Update/upgrade the plastic clamp on the intake.
Vac/pressure test

 

[J D]

As long as the mating surfaces aren't damaged, the muffler leak is simple gasket. Check the bolt threads for carbon build up which may cause them to get "tight" before they are actually done up

 

[bigtuna]

Yes jd the bolts were carboned up, ill take a steel brush to them.and some temp loc tite and well go from there