Running in a new OEM top end?

[bullittman281]

What is everybody's methods for running in a new top end. I've nearly acquired all of the parts to get my 351/346xp up and running. Historically I've had mixed results. This is my first new OEM top end. Most all of my other builds have been Meteor or Golf pistons in re-used and re-claimed burnt cylinders. I've gotten anything from small scratched to full on destruction. I don't know if its a cleanliness thing or something else. I typically let it idle for a bit and once warm give it juice. A few small cuts and then go big. Best results were with a new Meteor cylinder and piston that was let idle for most of a tank of gas before touching the throttle. Still some light scratches in the piston. None of my problems are from being too lean. What is everybody else's technique for running in a new top end??? Let me know. Thanks!!!

bullittman

 

[Vintage Engine Repairs]

I have always been advised: Idle for a couple mins to warm it up, tune it on the rich side and then put it under good load. Don’t bog it, but a sharp chain, self feeding, tuned on the rich side under full bar length cuts for a few tanks is a good start. Don’t WOT off load, don’t let it idle for long periods, though before you turn it off, let it idle for a couple mins to cool down.

Your aim is to force the rings, through the compression of the engine, against the cylinder walls and to bed them in.

some people say they feel an instant change in the saws performance when it breaks in, I never have, I have just found that the saw gradually pulls better in the cut every tank or so, tunes easier and runs better all round.

 

[link]

40/1 oil, let it idle to get warm, only small cuts the first few tanks; this allows for a constant variation of rpm, not a specific rpm for long.
Except for the 40/1 oil wich is usually not neccesary for proper quality stuff, this is standard procedure for any engine to run in.
I allways let it run a little at idle before i stop it.

 

[Woodslasher]

I've gotten anything from small scratched to full on destruction.

bullittman

That ain't right. The only times I've gotten scratches in a fresh build is when there's still transfer in the cylinder of when the big end bearing was breaking up. It sounds like you're missing a step somewhere.

 

[bwalker]

Warm it up to operating temperature and then run it like you stole it.

 

[Backstage]

That ain't right. The only times I've gotten scratches in a fresh build is when there's still transfer in the cylinder of when the big end bearing was breaking up. It sounds like you're missing a step somewhere.

This. It’s the big red flag in the op. New oem cylinder/pistons burning during breakin? Repeatedly? Something else is the issue.

I’m going to throw Foreigh Object Contamination into the hat. A metal shaving from a burr grinder will do that. Clean parts well and ensure they stay that way until you get an air filter screwed down.

Another possibility is pre oiling. I like to use straight two cycle oil and lightly coat everything. Otherwise you’re running dry and rough on first start and until mix gets through the entire system.

Finally check for lean tuning, including air leak induced lean condition running. Doesn’t matter how you tune if it can pull as much air as it wants from places it shouldn’t get it. It’s like holding an AA meeting in a liquor store.

 

[bwalker]

40/1 oil, let it idle to get warm, only small cuts the first few tanks; this allows for a constant variation of rpm, not a specific rpm for long.
Except for the 40/1 oil wich is usually not neccesary for proper quality stuff, this is standard procedure for any engine to run in.
I allways let it run a little at idle before i stop it.

That is what we are told to do with 4 cycle engines with shell type bearings.
Two cycles have roller and ball bearings which require no break in. The only break in that takes place in a two cycle is seating of the rings to the cylinder wall. This needs to happen ASAP and only happens with high loads. Babying your motor under the guise of break in is counter productive.
When I raced snowmobiles the engine builder I used broke them in by making a series of full load dyno runs. By the end the exhaust pipes would be smoking hot! His motors always performed too.

 

[link]

That is what we are told to do with 4 cycle engines with shell type bearings.
Two cycles have roller and ball bearings which require no break in. The only break in that takes place in a two cycle is seating of the rings to the cylinder wall. This needs to happen ASAP and only happens with high loads. Babying your motor under the guise of break in is counter productive.
When I raced snowmobiles the engine builder I used broke them in by making a series of full load dyno runs. By the end the exhaust pipes would be smoking hot! His motors always performed too.

Yes, I think perhaps a highend machined chainsaw engine like a Stihl or Husky or Echo probably dont really need any run in at all.
I still like to try and give my engines a gentle start in life, my patience usually dont stretch it for too long though.

 

[raoul morejohn]

If you're not doing a leak down test before starting your missing a big step. Lots of piston cylinder sets need attention also. Look port edges over with a magnifying lens. Piston skirt's to. I always rinse bottom end out with mix and air if I didn't split the case. Bearing cages can hold evil stuff...

 

[Gord404]

IMO - I just tune in a fresh rebuild by starting them up and getting them tuned in as close as possible a slight bit rich on the high and go find a log and run them in, maybe a wot half cut through a 24" log half way and let it idle for about 30 seconds and check she isn't over heating badly- tune until it's right and repeat until I feel it's right, really won't break in by letting them sit there for the first tank and letting them idle, they have to be under load and yes if you are not doing a vac-pressure test you might not be getting at the real problem and once again IMO I use 40:1 mix.

 

[Huskybill]

I moly up the moving parts, add some oil and fire it up.

 

[SteveSr]

That ain't right. The only times I've gotten scratches in a fresh build is when there's still transfer in the cylinder of when the big end bearing was breaking up. It sounds like you're missing a step somewhere.

Add to this proper cleaning of reworked cylinders with hot water and dish soap to remove any grit. Not doing this will get the results that you are seeing.

 

[Huskybill]

I split the cases, wash them clean, install new crank bearings, seals, gaskets, piston, cylinder. Again pre lube it all.

 

[bullittman281]

Well, it LIVES!!
I only have a minute or two on it so its too early to tell. I'll see what tomorrow brings.

When building these things everything always get a good solvent bath and a hot water bath. Should be clean enough to eat off of. Thats part of why I scratch my head on past problems. All of them were using old and or very old and burnt cylinders. Most all of them were also 029s, 310s, and 039s. That may be part of the trouble. Ether stuff still wasn't clear or sometime things might just be worn out. Everything gets lots of prelube when it goes back together. All the bearing get a good squirt and the cylinder wall is oiled. Once together the piston gets another squirt for good measure. The mosquitos stand no chance when it fires up. One of these day's I'll try to get pics of the piston in the 039 that I rebuilt. Its eating itself for no good reason. I'll see what this one does and post an update. So far its done better than the 310 build.

Something else that I've never seen bad are crank seals. Never had a saw that had issues get fixed with crank seals. Pulled plenty of non runners out of the junk bin that needed a carb kit. All were suspect and junked for crank seals but I've never seen them go bad. Its always carbs and fuel lines. I'm not arguing that they can't or don't. I've just never seen it or them be bad enough to cause problems.

Bullittman

 

[KASH]

In all my 55 years of saw use I have only run into 2 cases of seal failure the first was on the first saw I ever ran my dads Pioneer 600 we had a hose clamp that you slid over the throttle to start it as it would not idle due to the seal leaking .We did not know it was a bad seal so we cut our firewood for ten years you had to keep your hand on the throttle or it would stall at idle.The other saw was a Partner R420 which was given to me the seal was so bad you could feel the air coming out on the pto side.
Kash

 

[BrettS]

I have always run them to get them hot then let it cool down, run it until it gets hot then cool down then you're good to go.

 

[bullittman281]

Good evening.
Here are a few pics of the cylinder and piston after a couple of tanks of gas. Not sure what the marks are and the scratches. Have a look and see. The couple of top ends I've done do this. Not sure why. Cold saw has over 160 PSI compression. Hot is over 140. Gauge only goes to 160. This is at 6500 Ft. so the numbers will be lower than those at sea level. Saw cuts well. The intake scratch can be felt with a sharp pick. No evidence of the same damage on the piston. Foreign object damage?? The rest of the marks are just marks. They can't be felt. I'm nor sure if this is a cleanliness thing. Not sure how to get things any cleaner than with hot soap and water. Squish was ~.025" with no base gasket. Squish was measured by crushing lead solder. Ring end gap was ~ .011". All of the parts are new OEM Husqvarna 346XP. Let me know if anybody has any thoughts. For now Its back together and I'm gonna run it. Thanks!


Bullittman

 

[huskihl]

Good evening.
Here are a few pics of the cylinder and piston after a couple of tanks of gas. Not sure what the marks are and the scratches. Have a look and see. The couple of top ends I've done do this. Not sure why. Cold saw has over 160 PSI compression. Hot is over 140. Gauge only goes to 160. This is at 6500 Ft. so the numbers will be lower than those at sea level. Saw cuts well. The intake scratch can be felt with a sharp pick. No evidence of the same damage on the piston. Foreign object damage?? The rest of the marks are just marks. They can't be felt. I'm nor sure if this is a cleanliness thing. Not sure how to get things any cleaner than with hot soap and water. Squish was ~.025" with no base gasket. Squish was measured by crushing lead solder. Ring end gap was ~ .011". All of the parts are new OEM Husqvarna 346XP. Let me know if anybody has any thoughts. For now Its back together and I'm gonna run it. Thanks!


Bullittman

Kinda normal, but maybe a little excessive if it doesn’t have much time on it. 2 places where dirt can hide are inside the air filter and muffler. Either one can cause the scratches.
The black streaks are normal on a saw with low runtime. They’ll eventually fade or blend in

 

[SteveSr]

Good evening.
Here are a few pics of the cylinder and piston after a couple of tanks of gas. Not sure what the marks are and the scratches. Have a look and see. The couple of top ends I've done do this. Not sure why. Cold saw has over 160 PSI compression. Hot is over 140. Gauge only goes to 160. This is at 6500 Ft. so the numbers will be lower than those at sea level. Saw cuts well. The intake scratch can be felt with a sharp pick. No evidence of the same damage on the piston. Foreign object damage?? The rest of the marks are just marks. They can't be felt. I'm nor sure if this is a cleanliness thing. Not sure how to get things any cleaner than with hot soap and water. Squish was ~.025" with no base gasket. Squish was measured by crushing lead solder. Ring end gap was ~ .011". All of the parts are new OEM Husqvarna 346XP. Let me know if anybody has any thoughts. For now Its back together and I'm gonna run it. Thanks!


Bullittman

Based on the photos it looks like you are getting contamination from somewhere. Either grit that was in the saw when it was assembled or grit that is being pulled in through the air filter/intake... Are the crank seals new? That would be another place to pull in contaminated air. Possible leaking decomp valve?

 

[SteveSr]

Kinda normal, but maybe a little excessive if it doesn’t have much time on it. 2 places where dirt can hide are inside the air filter and muffler. Either one can cause the scratches.
The black streaks are normal on a saw with low runtime. They’ll eventually fade or blend in

Carbon / crap on the piston crown looks pretty bad for only a few tanks of gas. What are you using for oil and gas? How is the tune?