New saw, pdi check at full revs on first start...! Really..

[spudulike]

You need to rev a saw with non AT carb flat out to tach tune the carb to ensure the carb is acting as a rev limiter keeping the saw to under the maximum revs irrespective of any limiter on the coil.

Would I take a freshly rebuilt saw or new saw and rev them flat out...nope, I would build up heat first of all. Would it do damage - probably not if everything is working as it should and is unlikely to seize with the saw not being under full load.

Saws are designed to be run flat out or on idle.

When they are new, the rough surfaces of the ring, piston and bore need to be abraded together to form the best seal between surfaces whilst they are still a little rough and able to do so. This is done for revving it flat out for short periods so no going at a 3' ring with a new saw, short smaller cuts flat out with periods of cooling between cuts. Leaving a new saw idling for a long period is not the way to do it!

[Sambo]

30 minutes ago, doobin said:

You're always flat out in the cut but then the resistance from the chain is preventing it from revving out. Same as fith gear in a vehicle does. But no excuse for revving flat out from cold on a PDI. Only time I would use WOT with no load on the machine is when setting a high screw to ensure fourstroking and not too lean a mix.

 

That said, isn't WOT with no load on the saw for about thirty seconds part of the reset procedure for Mtronic gear?

I think on the latest calibration version but it doesn't actually reach full revs - it sort of bumbles about till it's running right and steps down again ?

[Sambo]

12 minutes ago, spudulike said:

You need to rev a saw with non AT carb flat out to tach tune the carb to ensure the carb is acting as a rev limiter keeping the saw to under the maximum revs irrespective of any limiter on the coil.

Would I take a freshly rebuilt saw or new saw and rev them flat out...nope, I would build up heat first of all. Would it do damage - probably not if everything is working as it should and is unlikely to seize with the saw not being under full load.

Saws are designed to be run flat out or on idle.

When they are new, the rough surfaces of the ring, piston and bore need to be abraded together to form the best seal between surfaces whilst they are still a little rough and able to do so. This is done for revving it flat out for short periods so no going at a 3' ring with a new saw, short smaller cuts flat out with periods of cooling between cuts. Leaving a new saw idling for a long period is not the way to do it!

I think the origin of this thread was the dealer taking a brand new, stone cold machine and revving it full bore - your angle is coming from a highly knowledgeable, experienced technician so I appreciate your comments. I think it's important to get across the point that you've got to treat a 2-stroke machine with a deal of care. My old boss used to leave new saws bumbling away for ages outside the workshop - I always wondered if that was a waste of time!

[Stubby]

38 minutes ago, Sambo said:

 My old boss used to leave new saws bumbling away for ages outside the workshop - I always wondered if that was a waste of time!

I think that is bad for them . Ticking over for ages means they are getting little fuel therefor little oil .  Possible glazing of the bore ? I think its ok to hold a new saw WOT as long as its in the cut .  That way its getting max oil but not over revving .  I would not hold one at WOT in fresh air . As Steve says get em warmed up first and have a bit of common sense/mechanical sympathy . 

[Moose McAlpine]

22 minutes ago, Stubby said:

I think that is bad for them . Ticking over for ages means they are getting little fuel therefor little oil .  Possible glazing of the bore ? I think its ok to hold a new saw WOT as long as its in the cut .  That way its getting max oil but not over revving .  I would not hold one at WOT in fresh air . As Steve says get em warmed up first and have a bit of common sense/mechanical sympathy . 

 Spot on.

 

New engines running at idle too long results in "cylinder polishing" where the bore becomes too smooth, doesn't retain oil film and then results lower compression, premature wear, etc. (And high oil consumption in pressure-lubricated engines.)

 

While new engines shouldn't be excessively revved, they also shouldn't be babied too much. The rings need to be seated to the bore so the two bed in correctly together, this needs higher cylinder pressure so it needs some load on it.

[Sambo]

2 hours ago, Stubby said:

I think that is bad for them . Ticking over for ages means they are getting little fuel therefor little oil .  Possible glazing of the bore ? I think its ok to hold a new saw WOT as long as its in the cut .  That way its getting max oil but not over revving .  I would not hold one at WOT in fresh air . As Steve says get em warmed up first and have a bit of common sense/mechanical sympathy . 

Mechanical Sympathy - spot on term! I'm stealing that! ?

[Sambo]

I do like it when a saw does bed in. Some machines achieve power gradually but for others like my new little MS151T it seems like they suddenly boost up! Is there any reason for this?!

[spuddog0507]

On 14/10/2019 at 13:44, wakefield tree surgeons said:

Yep..!! i spoke to stihl direct today,, in request of replacement or money back... as its a day old,, i im propsing,, its damaged from pdi check misconduct.....

 

Yet to get a reply...  seddons are refuseing any of the above...  Stihl wont hold there hands up for replacement...  Havent got the time to play games,,  But hay-ho here we go...

Thanks for all the info...  

They dont like it up em....!!!  but can give it,,

I havnt read all the other posts past this one, last post on first stage, i would be talking to trading standards and i would be telling Stihl UK that and dont take any shit off them i am sure you will be in the right, it all sounds like a massive headache to me that dont need to happen, good luck with it all,

[Stuarts]

So I might be being a bit thick here...the issue is ‘possible damage’ due to the full revs in pdi, or there has been actual damage due to the pdi?