EZ GO ST350 2004 (MCI engine) running rough and smoking

[Subarumouse]

Hello

Better late instead never...

The rods can't be machined to fit the (same) cranck.
Only when you buy some bearings between the cranck and rods.
(Is better for higher revs)
Otherwise buy some new rods.

Before buying new rings, look if the pistons aren't oval and measure them to get the right ringsize.

So the engine is already open and the valves are okay, lap them on their seats and get some new "things between valve and head to keep the oil out of the burningchamber", (can't get the name of them).

Get oil everywhere befor building it together.

Benno

[mjf1604]

Thanks Benno, putting bearings between the rods and crank does seem a good idea. I have to say I was surprised to find the rods just bolted straight onto the crankshaft, most auto engines I have worked on have small inserts called shells in the rod ends which are replaceable so the rod itself doesn't have to be replaced when this happens, making for a much cheaper repair.

What would I need to do to add bearings to these existing rods, and are the parts to do this readily available? if so where from?

I have checked the cylinders (i assume this is what you mean) and they are a little oval, but only very slightly, the reasonable level of compression the engine had its making me think the wear isn't terminal, and a rebore unnecessary - or am i being over optimistic? Its the rings that look more worn, they have completely lost their shaped side profile (as shown in the engine rebuild manual) and are just flat, hence I am thinking they are the main problem.

Also thanks for the advice on the valve stem seals, I had overlooked them. I will be sure to replace them! I want to make sure it runs good with no nasty rattles and smoke after all this effort!

Thanks for your help
M

[Subarumouse]

Hello,

You can get those bearings at a racekartshop.
Maybee they can build them in or they have a machineshop in the neighbourhood.
They have to drill out the rod and make the bearings fit with the apropriate measurements.
They also grind them in on the cranck..

http://karting.4cycle.com/index.php?
http://www.kartfinder.com/

Maybee this sites can help you
Look at fourstroke Honda, Briggs and Robin.

Benno

[mannyvillegas]

The connecting rods are bolted directly to the crankshaft. No in-between conrod bearings like the Yamahas.

On the white smoke issue, could be some water in the gas? Have you totally replaced the gasoline?

[mjf1604]

Just to update everyone, I have finally finished rebuilding the engine, and aside from a few issues with the throttle and governor cables that I have yet to address all seems a lot better.
I ended up replacing more than expected, including the connecting rods but it was worth it while it was all in bits. New piston rings fitted great and according to the manual were within spec so it didnt need re-boring which was good. The old rings were very warn, and may have even been the wrong part fitted before I owned it, and were letting a lot of oil past - hence the smoke.
Started up after a little cranking to lots of black sooty smoke - no doubt from the exhaust box that I burned out with gas to clear out the carbon build up.
After a few mins of running this all cleared and it sounded pretty good. The exhaust bolt threats in the head are not brilliant due to a previous owners attempts to work on it and over tightened them. So I intend to re-tap these to a slightly larger size so I can bolt the exhaust up properly and stop the blow I currently have around the gasket. Hopefully this will quieten it down somewhat to.
Thanks for all your help everybody, its helped get my ST350 back up and running. Hopefully wont be to long before I get the final few bits done on it and will be fully functional once more.

One final question however - I have noticed on the general maintenance section of this site that there was a recall on the MCI engine shortly after it was introduced, as it needed a modification to the carb. Is there anyway I can tell if this has been done!?!?!?!?

thnx again

Mark

[mjf1604]

Just to update everyone, I have finally finished rebuilding the engine, and aside from a few issues with the throttle and governor cables that I have yet to address all seems a lot better.
I ended up replacing more than expected, including the connecting rods but it was worth it while it was all in bits. New piston rings fitted great and according to the manual were within spec so it didnt need re-boring which was good. The old rings were very warn, and may have even been the wrong part fitted before I owned it, and were letting a lot of oil past - hence the smoke.
Started up after a little cranking to lots of black sooty smoke - no doubt from the exhaust box that I burned out with gas to clear out the carbon build up.
After a few mins of running this all cleared and it sounded pretty good. The exhaust bolt threats in the head are not brilliant due to a previous owners attempts to work on it and over tightened them. So I intend to re-tap these to a slightly larger size so I can bolt the exhaust up properly and stop the blow I currently have around the gasket. Hopefully this will quieten it down somewhat to.
Thanks for all your help everybody, its helped get my ST350 back up and running. Hopefully wont be to long before I get the final few bits done on it and will be fully functional once more.

One final question however - I have noticed on the general maintenance section of this site that there was a recall on the MCI engine shortly after it was introduced, as it needed a modification to the carb. Is there anyway I can tell if this has been done!?!?!?!?

thnx again

Mark