OutdoorKing Repair Forum Forums Repairs and Maintenance Questions on Chainsaws and Concrete Cutters Petrol Chainsaws and Concrete Cutters Homelite Super Mini

Hi there, I have been looking over an old Homelite chainsaw and it looks like a unit to be resurrected. I tested the compression and it read 205 psi. This would be the highest reading I have come across. It there a point where compression is too high? If so can it be carbon build up?

I have tested many machines and my gauge seems to be reasonably reliable.

If I recall correctly my old Buick 215 cubic inch aluminium V8 gave about that pressure, but being the Powerpak option it had 11 to 1 compression and a 4 barrel carburetor. It seems very high for a chainsaw.

The main limiting factor to compression ratio is detonation. As the ratio increases, higher octane fuel is required. It may also be a factor in causing carbon accumulation - my old Buick engine had a very severe problem with that, because I put it in an MGB that only weighed 2000 lb, then drove it to work every day in the Melbourne traffic.

I think your saw probably either has a lot of carbon in its cylinder head, or more likely has been fitted with incorrect parts, such as a piston with a higher compression height (the distance from the center of the gudgeon pin to the top of the piston crown). In the good old days we used to do that to cars a lot. The ideal "improvement" to an old Triumph TR2, 3, or 3A was to fit Ferguson tractor cylinder sleeves (which increased its cubic capacity from 1.6 to 2.3 litres) and Chevrolet 6 pistons, which not only had the correct diameter to suit the Ferguson sleeves, but also increased the compression ratio to 10:1. This did wonders for the performance, but the heat rejection was a bit excessive for the original radiator. To be honest, there was an additional attraction to this modification: the Ferguson sleeves, being for farm equipment, were free of the 30% sales tax that applied to car parts. As an aside, the reason the Ferguson sleeves fitted the Triumph TR sports cars was that both tractors and sports cars used the 4 cylinder engine from the Standard-Triumph Vanguard car.

You might be on the right track there Grumpy. The saw looks like its done some work. The exhaust port is carboned up yet looking through the plug hole shows the piston top to be very clean. I'll get my sons school provided trusty dental mirror and peek up at the head and see what's there. In terms of appearance I reckon its one of the coolest looking saws I have seen. Chrome starter cover and two tone paint on the sides with a chequered flag. On the shelf as a new one it would have looked great.

I'll be interested to hear the results aldot, especially if it has the wrong piston fitted. I'd expect it to ruin its starter mechanism pretty quickly with that compression pressure.

Even more interesting. I pulled the starter down and it is seriously built like a tank. The starter on this little saw is built far stronger than the starter on the the 103cc Pioneer. There is no plastic and what looks like a brass bush that is grooved for lube perhaps.

The fast idle throttle lock seems to be linked to a decompressor. I guess these items might point to a high compression machine.

A few other owners have reported compression tests around the 180-195 psi. Apparently they then released a lower compression version where plastic components were used in the starter mechanism.

With a strong starter mechanism and a decompressor, it sounds as if it was designed for an unusually high compression ratio. Provided it doesn't accumulate carbon or detonate, that is all to the good. As long as you run it on full song, it isn't likely to accumulate carbon anywhere except maybe the exhaust port.