Compression tests

[kram]

Tested my kit today, I'm wondering what a good result should be. All were checked after warming up, filter removed, throttle open. Using one of these Husqvarna testers

https://www.lsengineers.co.uk/compression-tester-genuine-husqvarna-part-531-03-16-86.html

 

G372XP, around 130psi. Runs ok but cyl has some marks.

Hyundai blower, 140psi.

 

020T 145psi.

 

McCulloch CS340 195 psi. That was a suprise, used to run great but the carb needs some adjustment.

 

Lidl 53cc, 215 psi.

Edited January 17 by kram

[spudulike]

That gauge looks like the Gunson Hi Gauge.

A standard 372XP - 150-170, Modified - 185+psi

MS200T, Standard 150 on an old one, 175 on a new cylinder, 200+ modified.

The rest, no idea what they are.

 

[Mark_Skyland]

Hi compression on the cheap machines!

 

[kram]

16 hours ago, Mark_Skyland said:

Hi compression on the cheap machines!

 

It is interesting as their spec is underpowered for the displacement and the McCulloch atleast, is underpowered, but a high compression should give more power?

Either way, they do the job and adequate for the little ground work I do.

 

The G372XP, I am thinking of getting a better pattern cylinder kit. Meteor and Hyway seem to get good reviews?

 

 

I have a few more to test, BG86 blower to test, its down on power but the cylinder looks good, looking through the exhaust.

An earth auger, that previously siezed years ago, still runs adequately after cleaning up the piston and ring groove.

My Echo 2511T, runs great, I need to make a thread adaptor for the tester.

Edited January 19 by kram

[spudulike]

On these type engines, 175-230psi will give a decent gain in power, beyond this, combustion will be stifled as is seen on many very high revving two strokes...14,000 isn't that high compared to many racing bikes of the era where these compressions would be excessive.

If you have tested/run/modded many saw engines, you find that the difference between 150psi and 175 is like chalk and cheese in pickup, power, torque and chain speed under load. 

Your cheaper saws with decent compression may be being held back by muffler design, poor ignition advance, carb air flow and design, combustion chamber design, port duration and blowdown figures etc. Compression is just one part of the equation.

[kram]

I had to check the engine auger, knowing that it previously siezed. I couldnt find parts at the time so cleaned up best I could and reassembled. It ran well enough and did many more fence holes.

The original sieze was caused by the cylinder being only loosely assembled from new.

 

130psi is not bad, considering the abuse. Pulled it apart for a closer look, and its exactly as I remember, it has not got noticably worse and would still live if I reassembled it

 

 

 

 

 

I have ordered a couple of cylinder kits but the first is likely worse than whats on there, so thats being returned - porous casting with holes in the plating.

Edited January 24 by kram

[spudulike]

That is horrible and that big groove above the exhaust port isn't helping compression.

[peatff]

I'm surprised that ran in that state, is that a chunk out of the piston above the top ring ?

[kram]

Yes it ran well, very little change since I originally repaired it, I have just found a pic from when it originally siezed. The rings were stuck with alu smeared into the grooves, yes there was a lump missing above the ring.

 

I dont like having tools in a poor state like that, however it does not need any more power. If it hits a brick, large root or concrete, it can hurt or rip out your hands.

 

I dont expect to be doing any more fence holes. The 16:1 gearbox makes me think it might have some other uses.

[kram]

Looks like I will be putting the old cylinder back on the auger! I have ordered and now returned three aftermarket cyl kits. They all appear to be made from recycled cans, porous castings, holes in the plating.