Bad day for my Dolmars...

[tdi-rick]

Hope the barrel is OK Matt, and if it's just the base gasket that's the best possible outcome, although a pain it actually happened as it really shouldn't have. Someone in QC needs their arse kicked.

Approx 13-15Nm (150lb/in) is the bolt tension for the cylinder/crankcase bolts if anyone wants to check theirs.




For a week or so I almost thought I might have scored a cheap barrel to try out some revised porting :greenchainsaw:

 

[MCW]

Hope the barrel is OK Matt, and if it's just the base gasket that's the best possible outcome, although a pain it actually happened as it really shouldn't have. Someone in QC needs their arse kicked.

And thanks for emailing me that workshop manual Rick, the Husky guy thanked me for passing it onto them.

 

[E.V.A. Sawman]

Another way we use to check for external air leaks on motors is to take off your engine top covers (leave air filter on) and spray around carb boots, cylinder base,etc. with contact cleaner. Make sure it is not corrosive type to plastic. Start engine let idle and spray areas to check. If there is a leak it will cause engine to stall or stumble. This will work on 2 and 4 cycle engines. It is not foolproof but it is another tool that sometimes helps.

 

[MCW]

Another way we use to check for external air leaks on motors is to take off your engine top covers (leave air filter on) and spray around carb boots, cylinder base,etc. with contact cleaner. Make sure it is not corrosive type to plastic. Start engine let idle and spray areas to check. If there is a leak it will cause engine to stall or stumble. This will work on 2 and 4 cycle engines. It is not foolproof but it is another tool that sometimes helps.

I agree but not idling and over revving without touching the throttle was the problem. Impossible to test it like this in my case as saw wouldn't idle unfortunately.

 

[7sleeper]

Old thread but just thought I'd let people know what was up with my 7900. Local Husky guy has had it for a while now but been too busy to take a look. I didn't take it to the local small engine "expert". Luckily I heard a few bad things about him the same day I was going to drop it in, good with outboard motors and lawnmowers, hopeless with saws
Problem was a "blown base gasket". Dealer wasn't exactly sure whether that is the cylinder gasket (965 531 121) or crankcase gasket (038 111 042) as the tech guy had gone home for the weekend. Apparently a couple of screws/bolts had loosened off and popped the gasket out the side - therefore a major vaccum leak. 7900 was a September '06 model. Anyone with a 7900 of that vintage probably should check all their bolts and screws just to be sure.
New part ordered and will be fixed early next week.
Although the 3120 was fun to begin with I'm sick of using it for medium sized trees and look forward to the 7900's return.
5100-S has been running like a clock ever since and hasn't skipped a beat. I think it was just very badly flooded and I didn't dry the plug out enough when looking for a spark, so no faulty coil.

Happy it all worked out for you!

7

 

[B_Turner]

Had to cut the remainder of the relatively small trees up with my 3120XP and 42" bar. After 5 hours I'm a bit stuffed :censored

SHould have taken the bar and chain off the 7900 and put it on the 3120.

Hope all is getting resolved.

 

[Termite]

I had the coil go out on my 5100 back in December. It was replaced under warranty. I think it was intermittent before it finally quit completely.

 

[MCW]

SHould have taken the bar and chain off the 7900 and put it on the 3120.

Good plan but had the .404" sprocket on the 3120 and no spanner/socket to get the clutch off to change it to 3/8".
3/4" socket added to my toolbox shortly after

 

[B_Turner]

Good plan but had the .404" sprocket on the 3120 and no spanner/socket to get the clutch off to change it to 3/8".
3/4" socket added to my toolbox shortly after

Whoops. I run 3/8 on my big saws and bars and forget that everyone doesn't.

Nice having the same chain and I've had no issues so far with breaking or stretching.

And cuts like crazy.

 

[MCW]

Whoops. I run 3/8 on my big saws and bars and forget that everyone doesn't.

Nice having the same chain and I've had no issues so far with breaking or stretching.

And cuts like crazy.

I'm thinking of running 3/8" too one day but unfortunately made a heap of .404" chains up and stocked up on .404" bars before I realised I should have just stuck with 3/8".

 

[MCW]

Back again. Dropped in at the Husky dealer and took a photo of where the gasket blew out on my 7900 after bolts loosened off. Thought I'd post the pic. Good to see that the bore and piston were like new. Realised I've gone through 6 litres of 2 stroke so this saw has seen around 300 litres of mix through it, not 200 litres like I previously thought. Without filter oil I'd hate to see the bore and piston...
Quite obvious. Bottom left part of gasket in picture.

 

[tdi-rick]

Matt, only just thought, you should have had him do a squish check without a gasket, and if it was still 0.020" or greater, just used some Loctite 518, check compression to make sure it isn't excessive and you're back in business with a little more grunt to boot.

 

[SawTroll]

Matt, only just thought, you should have had him do a squish check without a gasket, and if it was still 0.020" or greater, just used some Loctite 518, check compression to make sure it isn't excessive and you're back in business with a little more grunt to boot.

Doesn't that mean that you will need to do some port work as well?

 

[husq2100]

Doesn't that mean that you will need to do some port work as well?

depends what your after regarding the power range...

with the small amount the jug will drop without the gasket it wont make too much a difference, but the difference would be more towards torque than top end power.(if im thinking right:monkey which wouldnt hurt Matt with the hardwood he cuts and running 3/8 on a 18" bar

im either on the right track or just made an ass of myself(which i excell at )

Serg

 

[tdi-rick]

depends what your after regarding the power range...

with the small amount the jug will drop without the gasket it wont make too much a difference, but the difference would be more towards torque than top end power.(if im thinking right:monkey which wouldnt hurt Matt with the hardwood he cuts and running 3/8 on a 18" bar

im either on the right track or just made an ass of myself(which i excell at )

Serg

yep
(it helps torque, not making an ass of yourself :greenchainsaw: )
You are dropping the exhaust slightly, so it opens a touch later which helps torque and will probably knock a little off the top end.
How much depends on the saw and how much you drop it, but usually the gain in useable compression (power) more than offsets the slight change in characteristics.

It used to be the first thing that was done to KT100S Yamaha kart engines years ago here as you couldn't touch the ports (that and the ignition timing set to 0.5mm)

Squish, from Bell.

However, if you want top power and no risk of detonation, the squish clearance
must be closed up. A squish band that isn't working is worse than no squish band at all
as it wastes part of your fuel/air charge. Wasted fuel charge spells less horsepower.
To give you an idea of how much horsepower you could be losing it would be good
to consider the example of a TZ250 Yamaha road racer. These engines have a bore
54mm in diameter and an offset squish chamber. The compression ratio uncorrected is
about 15:1, meaning that the trapped charge is compressed into a space 8.8cc in
volume. If the squish clearance is 1.7mm (lots of motors come from the factory like
that) 1.94cc of the trapped charge will not be burned until well past TDC, too late to
produce any power. 1.94cc represents 22% of the inlet charge lost. When the squish
clearance is reduced to 0.8mm the charge loss is reduced to 0.92cc or 10.5%. On paper
it would seem an easy way to pick up 11.5% more power, but losses reduce this increase
to about 5-6% on the dyno. Therefore maximum power goes up from 52 to 55 hp. Midrange
power can rise as much as 10%, so the bike is easier to ride and it doesn't
detonate.

 

[MCW]

Pass on the porting
I'm a sucker for more grunt when I get a sniff so she'll be staying stock. It runs everythingup to 32" just fine so I'll use my 3120 above that - the Husky certainly takes care of any power urges I have as far as saws go.