Lost compression

[reymund77]

The cylinder came back from the machine shop....looks ok...use my finger nail to feel...smooth....shld I start looking for a 240cc kit or another block or jus use back and put in new Wiseco 69.0mm or move up to 69.5?

Put the stock piston into the block....fit seems ok thou

My stock piston

[Indawoods]

WISECO!

[fuzzy]

2nd the wiseco, but why did the cyl go to the machine shop? It shuold've been bored for a specific piston size! Was it replated? Doesn't look plated or sleeved? 240cc kit, bore size, etc, should all be decided before trip to machine shop.

[80elkster]

Question;
You said you topped off your gas tank at the pump in a previous post. Did you put any pre-mix oil in with that gas? I sure hope you did or is it an SR model and do those have an oil injector? Somehow it has to have oil getting to the piston rings lower and upper bearings.

[canyncarvr]

Re: 'but I did notice when I top up fuel at the gas station...water/coolant like dripping bit by bits from a hole below the water pump casing near the drain plug of coolant after I stop my engine.'

That is a weep hole that allows coolant getting past the seal to get out of the engine...as opposed to contaminating the crankcase. Shouldn't be leaking ater it was replaced.

If the bike quit due to coolant loss, that wouldn't generally get you a hole in the piston crown. The piston would stick 'cuz it got hot..but there wouldn't be any lean condition (not much of one) or spark problem (too much advance) that would dig a hole in the piston.

There was something else, likely. Air leak (way lean) maybe.

You don't run a projected tip plug, do you? If you did...don't.

How old WAS the plug? I've had a hole beat in the top of a piston that started with a plug failure..the plug itself came apart. Once you get a bit of metal pounding on top of the piston you end up with edges (around the pit that just got pounded in) that tend to get real hot with combustion. That heat eats the edges, makes a bigger hole, which ends up with more edges, etc. etc. Pretty soon...there's a hole where there ain't supposed to be one.


You may not have to replace the reeds..but at the least get them out and clean them. There WILL be aluminum bits everywhere inside the engine...and that includes the reeds/reed cage.

Re: ' put in new Wiseco 69.0mm or move up to 69.5?

I answered that earlier. Why ask it again? Didn't read it...or didn't understand it?

Check that cylinder with a magnet. If there is NO stick..there is NO plating..and the cylinder is worthless in it's current condition.

[reymund77]

2nd the wiseco, but why did the cyl go to the machine shop? It shuold've been bored for a specific piston size! Was it replated? Doesn't look plated or sleeved? 240cc kit, bore size, etc, should all be decided before trip to machine shop.

Sorry bro...still figuring out what the mech had did to the cylinder...fren was sharing that he might just sent it for honing to removed those aluminum bits that "weld" onto the cylinder and honing removes them..piston nvr detonate so cylinder wall is not scratched/damaged...have to get the mech to measure the current cylinder bore now and like wat cc advise and use magnet to check nikasil condition...

Mine is a SR but I've replaced with a R crankcase, gearings, bearings etc so have to use premix and not more oil injector...and I certainly nvr forget to top up oil into my gas tank directly.

Plug was about 6mths old...sorry, dun understand whats a projected tip plug was or look like...will head down to the bikeshop after work and take note of the part number etc.....could that also be a issue?...how often do you guys change plug?...I've got the bike Feb 08 and had not changed a plug since....it nvr foul on me and it start the bike easily

So if the weep hole still leak, could there be an installation problem when replacing the waterpump seal and oil seal/bearing?

Another good way to tell or spot air leak?..it seems to be a big killer and blew a hole thru my piston

[canyncarvr]

Re: '..sorry, dun understand whats a projected tip plug was or look like...'

You would have to go to a good bit of trouble to GET one as they are not commonly available....so you would know it if you had one. I wouldn't worry about it.

I wouldn't run a smaller tip than an -EG. Somewhere in this thread you said you used an EIX (.6mm tip) plug, I think? An -EG plug works well..a bit better performance than the fat-tip -ES, not the cost of a rare metal -EIX, not as small a tip.

Re: 'How often do you guys change plug..'

Likely not often enough in my case. I tend to forget about it. I don't know of any 'rule of thumb' for changing plugs. Six months sounds good to me... maybe a bit much. Obviously that would mean you ride the thing a good bit. A year should work OK, too. For whatever reason (meaning none in particular) I don't want to keep a plug in for over a year.

Re: 'So if the weep hole still leak, could there be an installation problem when replacing the waterpump seal and oil seal/bearing?

Yes. There could also be a problem with the shaft itself. Putting an 'old' shaft in a 'new' seal isn't the best choice. If there is a wear spot on the shaft it might not match up with the tip of the new seal. In any situation you are better off replacing 'stuff' that is a matched set..that has 'worn in' together.

Try replacing a pinion gear...but using an old RING gear. Ha! You will NEVER get it right. That's why no one ever DOES that.

No....a ring and pinion isn't 'the same' as a water pump shaft and seal, but you get the idea.

Re: 'Another good way to tell or spot air leak?..'

A number of them. Leak down tests (pressurizing the case, looking for leaks with soapy water sprayed around every possible spot), spraying starting fluid on questionable spots while the engine is running, listening for an RPM change). The latter method a bit tough to do if crank seals are in question.

The best way to not have a leak is to pay attention to the put-together process and have a clue about it in the first place. Don't do dumb things like reusing a base gasket. Don't use a screwdriver to pry the pieces apart on disassembly. Don't assume you know what 18ft/lb (example figure) of torque is.