365 special acquired for $50

[Cas101326]

What does all this sign on the piston mean? I got to looking at it today through spark plug hole and cylinder looked so I good I took and turned the flywheel backwards just a tad and it came loose. Poured some 2 stroke oil in and started slowly pulling the rope and it got free. Popped compression test and it was 90, so I pulled the jug when I got home and this is what I found. I believe I can clean up the ring groove and put it back together if it won’t hurt anything for now, to be sure everything else is operational. If crank is good (which it seems to be good and tight, but when the piston gets to TDC there seems to be a slight bind or something when you turn it slow, but when it’s pulled faster its not really noticeable) and everything checks out good, I’ll buy a new piston and all and go ahead and get her wood ready. Just wanted t hear some thought before I do that

 

[ken morgan]

They do have the same cases. And I feel that this case capacity is better suited to the 365.

gotcha, so you think that the stroke and displacement of the 372 do not meld well with the case design and that in fact said case volume actually works better for the bore and stroke of the 365. that makes sense to me. Please correct me if i am still not getting your point.

 

[ken morgan]

View attachment 673057 View attachment 673058 View attachment 673059
What does all this sign on the piston mean? I got to looking at it today through spark plug hole and cylinder looked so I good I took and turned the flywheel backwards just a tad and it came loose. Poured some 2 stroke oil in and started slowly pulling the rope and it got free. Popped compression test and it was 90, so I pulled the jug when I got home and this is what I found. I believe I can clean up the ring groove and put it back together if it won’t hurt anything for now, to be sure everything else is operational. If crank is good (which it seems to be good and tight, but when the piston gets to TDC there seems to be a slight bind or something when you turn it slow, but when it’s pulled faster its not really noticeable) and everything checks out good, I’ll buy a new piston and all and go ahead and get her wood ready. Just wanted t hear some thought before I do that

whats the cylinder itself look like?

 

[Cas101326]

I know you can see some sign, but I can feel it AT ALL. It’s very smooth. In fact it’s probably the smoothest cylinder I’ve fooled with. If you were blind, I believe it would pass for new

 

[ken morgan]

I say clean it (cylinder) up and replace the piston/rings. looks like it was run lean for a long period of time....not straight gassed, but just lean. thta or really ****** gas. the pitting and melting of the crown indicates (or would indicate on a 4 stroke) that it was pre-igniting and getting detonation...that's from either too lean, or bad timing. Being the timing is set on these and not adjustable (from the factory) I would go with either bad gas, or a slightly lean condition over an extended period of time.

 

[huskihl]

gotcha, so you think that the stroke and displacement of the 372 do not meld well with the case design and that in fact said case volume actually works better for the bore and stroke of the 365. that makes sense to me. Please correct me if i am still not getting your point.

You're understanding my point now.
It's good for a 372 also, don't get me wrong. A 372 can be built to compete with much bigger saws. But a 365 is no slouch either, and shouldn't be discarded just because of the 7cc difference in displacement

 

[Cas101326]

In this picture I posted before, you can’t tell it, but it’s pitted up in the area I marked in red very much like the piston is. I put new piston in saw and deleted base gasket with some yamabond4, cranked it up and let it idle for about 10-15 minutes last night and checked compression when I cut it off and it was only at 135. I know a hot reading differs than cold, but with a base gasket delete I was disappointed in compression readings. Could this pitting be the cause of it, or could I have not put enough Yamabond on the base? I’m not sure what to do, and maybe I’m being hard to please with a used cylinder, but I was expecting more

 

[Cas101326]

Here’s a pic of the piston I pulled off of it for reference

 

[suttererman85]

There is a kit I’ve seen somewhere that has all the stuff to go to a high top/hd filter setup. Want to say it was around $70 on eBay perhaps.


Sent from my iPhone using Tapatalk

 

[suttererman85]

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/232728685656

Here it is.


Sent from my iPhone using Tapatalk

 

[rupedoggy]

Looks to me like something danced around on the top of the piston. 135 compression is probably all you will get. Did you use an aftermarket piston? They don't do so good on compression.

 

[Big Red Oaks 4 me]

Ya' done good!

 

[Deleted member 117362]

View attachment 676423
Here’s a pic of the piston I pulled off of it for reference

Look over all bearings and cages, seen that several times. Last one had a lower rod bearing cage break up. Some have had a case bearing let go of a few pieces of cage. Pieces get pounded by piston on squish band.

 

[ken morgan]

Looks to me like something danced around on the top of the piston. 135 compression is probably all you will get. Did you use an aftermarket piston? They don't do so good on compression.

anything that danced around would have taken out the port on the way out. That is pitting from detonation...crappy fuel, or slightly lean over a long period of time.

 

[cus_deluxe]

There might be some detonation that went on but theres no doubt that that thing ate something. Seen it plenty of times where stff gets spit out and ports are fine. Look at the different shapes of the pockmarks. That is not detonation. Id be looking that crank over really well, and replace bearings and seals for peace of mind.

 

[Deleted member 117362]

View attachment 676684 There might be some detonation that went on but theres no doubt that that thing ate something. Seen it plenty of times where stff gets spit out and ports are fine. Look at the different shapes of the pockmarks. That is not detonation. Id be looking that crank over really well, and replace bearings and seals for peace of mind.

+1

 

[rupedoggy]

+2 engine failure analysis is not your strong point Ken.

 

[ken morgan]

+2 engine failure analysis is not your strong point Ken.

My engines run for multiple sessions on the track and I have melted pistons and rotors and they looks like that. mine was due to advanced ignition timing under high heat and stress (and boost) over a 30 minute run on a 1.5mile road course so Think what you want. The other things that offer similar characteristics are running slightly lean, or old fuel that's knock resistance (octane rating) has diminished due to sitting.

 

[Deleted member 117362]

Could be all of the above. Does not really matter much, needs to be completely repaired. Use Good piston, rings, bearings, gas, gaskets, seals, oil, crank and whatever else it needs.

 

[ken morgan]

Could be all of the above. Does not really matter much, needs to be completely repaired. Use Good piston, rings, bearings, gas, gaskets, seals, oil, crank and whatever else it needs.

agreed, whatever the heck happened time to fix it and move on to the next tree that needs cutting..