Can I reuse my piston on my 102?(pictures attached)

[pat777]

Just wondering if this piston is reusable or should I look for a new one? There is some scoring on the piston and there is a section that is gouged out. I have new rings on the way but should the piston be replaced also or will I get away with using it again? Could it effect the performance of the outboard if I decide to reuse it? Any ideas what could have caused this kind of damage to the piston? Should I reuse it or replace it? Thanks

[phil]

It looks bad. If it was mine, I would change pistons. Do you have a parts motor with a decent piston?

How does the cylinder look? It appears to have been run with a foreign object embedded in it for quite a while. Perhaps a piece of carbon residue or a small chunk of metal.

[pat777]

Hi phil

Thanks for the reply. No I don't have a parts motor with this one. Is it still possible to buy new pistons for the 102 or will I have to look out for a second hand one if I decide to change it. I was hoping that because the damage was below the piston rings that I might get away with leaving it in. The cylinder looks fine, I'll try and get a picture up later. I wasn't sure if it was a manufacturing flaw or what but I guess it wouldn't have passed a British Seagull quality inspection? There was no sign of any foreign object when it was taken apart, but it was fairly temperamental starting before it was taken apart, but that could have been for any other number of reasons.

Thanks for the reply, I'd be interested to hear other peoples opinions on the matter also. I'm using this as a working motor(hopefully, if it starts once it's put back together, so I'm not to worried about aesthetics as long as it's reliable and starts up and runs okay.

Cheers Pat

[THCL500J8]

There is a 102 piston and cylinder on ebay in Scunthorpe, UK for about 40 pound, it might be the smart move before someone else buys it.

eBay item number:
111298260085

That's my suggestion.

[pat777]

Thanks for the link THCL500J8. I had seen that one already. It looks to be in okay condition and I like the fact that it has the welsh plugs for gaining access to the waterways. The cylinder I have has the pressed in welsh plugs, which is not ideal, but the waterways are fairly clear all the same. I'm relatively new to seagulls so I appreciate any and all advice but at the same time I don't want to be replacing parts unless it's strictly necessary. Would the damage on this piston actually have any effect on the performance and running of the outboard? Is it not the piston rings doing all the work with regards to the compression etc. I mean the cylinder bore is in very good nick on my 102 block.

Cheers Pat

[Stelios_Rjk]

Hi Pat,

Examine the piston and let me know please.
Is the red region darker than the rest of the piston? I mean, can you detect boarders as I draw them in red?
The mark the green circle shows has some depth, right?

[pat777]

Hey Stelios_Rjk,

Yes the green circle that you've highlighted has some depth to it perhaps 1-2 mm. Also with the red section that you have highlighted there is a darker area going all the way around the piston with a very slight step, so if you run your finger over the piston you can feel a change in height, perhaps the step is 1/4 mm to 1/2 mm(Hard to know for sure). I had not seen a seagull piston like this before with the change in level. I wasn't sure if it had been manufactured like this with the slight step. The 102 outboard is quite old 1953. Also there are some lines gouged into the piston running vertically below the green circle pothole.

Thanks Pat

[Stelios_Rjk]

OK then everything makes sense to me or it is science fiction

The red lines depicts the exhaust port of the cylinder. Possibly after use the engine stored with some water in the exhaust. Placed with the gearbox in higher position than the powerhead. Some water dripped and stood where now you see the dimple (green area). Aluminum corroded and get swollen a little bit. When the engine were used the next time, loose corrosion products detached and went between the piston and the cylinder while the engine was running. That created the nicks. The slight step (red line) is also created because of the corrosion but it wasn't so intense as the one created by the water.

Better to replace it. It will work as is but the corrosion on the dimple may create more loose parts during the years. I think that pistons used on centuries or silver centuries are the same as those used on 102 models but verify it before getting one.

[phil]

IIRC pistons from 102cc motors to at least 1977 should fit. I have an AC 102 motor that has been running with a Century or Silver Century piston, rod, and cap for at least five years.

[pat777]

Hi Stelios_Rjk

That sounds like a good prognosis of what might of happened to cause the damage on the piston. I think I might put it back together with this current piston and see how it goes with the new rings. I can always look out for a new piston and or cylinder head if I am still having trouble. At the moment I am only using the boat on the canals so I don't have too far to swim to get back to dry land if the outboard lets me down! I will make sure not to raise the gearbox higher than the powerhead. I generally store it upright on an outboard stand so this risk should not arise again. At least I haven't owned it for long so I can blame the previous owner for causing the damage!

Thanks also to phil for confirming that you have been running an ac 102 with a century piston.

Cheers Pat

[pat777]

Here are a few pictures of the cylinder bore as promised. It looks to be in very good condition to me. Thanks for all the help with the diagnosis of my problems.

Cheers Pat

[Stelios_Rjk]

Most welcomed! The whole picture jumped out of my head so I refer it. The bore looks clean and that's the important thing.
In case you see the engine running abnormal you will know what would be the No1 suspect!

Show us the engine when ready.



Cheers
S

[headdownarseup]

hi pat.
dont put the motor together with this piston in it. its scrap buddy!
the piston (to some degree) will be making some of the compression, the rest will be done by the rings. the localised corrosion on the piston skirt (below the rings and the "stepped area") will eventually lead to "BLOW BY" and the compression will suffer as a result leading to poor performace and difficulty starting and running.
have another look at the water jacket in the block. have a poke around inside the waterways with a stiff bit of wire (a straightened out bit of coathanger will do) and see if there are any flakes of rust coming out. next, try and blow through it.

stelios is also right in what he says. if the motor hasn't been drained off properly before putting away it will corrode the piston around the exhaust port.

from what i can see of the photos it looks like corrosion and cooling problems going on inside the block. it also looks pretty well coked up with carbon if i'm not mistaken. the hottest end of the cylinder will be around the spark plug area,and the parts of the water jacket that suffer quite badly are also in this area.(make sure its as clean as you can get it to promote better waterflow) and it will run cooler and make a bit more power?

basically all the 102 and century pistons will fit straight over. just a couple of slight differences in the transfer area at the top of the piston but pretty much the same.
hope this helps

jon

[JERSEYMAN]

A light hone on the cylinder, a good used piston and a new set of rings then you will never have to worry about that side of the motor again at least not in the next couple of decades, anything less is just false economy.

[pat777]

Hi jon

Thanks for posting a bit more information and for your opinion on the condition of the piston. So far everybody is telling me to change the piston, perhaps I should take the advice on board. I want the outboard to run as well as a 60 year old outboard can be expected to. It's a bitsa seagull that has been switched over to electronic ignition.

It's funny you should mention the water ways. That was the reason it was taken apart in the first place. I've not run it much since I've owned it. It used to pump water fine for about 10 minutes and then it would invariably stop pumping water. I initially thought this was a problem with weed in the canal but I figured that it must be something in the water jacket causing the trouble. I was surprised when it was taken apart that the waterways were clear enough. I'm sure there must something inside the water jacket that is blocking the passage of the water. As I mentioned earlier there are pressed welsh plugs on this particular block as opposed to the removable ones so there are a few parts of the water jacket that are difficult to reach.

Is there anything I can do to reduce the carbon build up in the block?

Here are a couple of pictures of it before it was taken apart, it won't look much different when it goes back together, I'm not really into painting and polishing stuff although I can really appreciate other seagull owners pristine restored outboards. After all this is a working outboard and not a museum piece.

Cheers Pat