Tear Down Pics MRC 100cc

Brandon Baldassi · Joined: 04 Apr 2010 Posts: 53

Decided to pull the head/cylinder off today. I would like to hear opinions on the engine. I believe I should start looking for a new piston. Also, it appears like the engine has had port work done at one time. How does it look to you guys?

I can take others if needed

Walt Gifford · Posted: Sun Aug 12, 2012 12:52 pm Post subject:

That is some sweet port work right there. Is that a Parilla TT-25? I've got torque plates for that. Looks like the bore needs honing.

Gif Cool

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Brandon Baldassi · Joined: 04 Apr 2010 Posts: 53

I believe it is an MRC engine.

Brandon Baldassi · Joined: 04 Apr 2010 Posts: 53

Howbout the piston? Am I due for a replacement ?

Walt Gifford · Posted: Sun Aug 12, 2012 5:23 pm Post subject:

The third pic the piston looks like it has some metal smeared on the side. A new piston is always good. If you're on a real tight budget it could be cleaned up with a file and some fine sand paper just to get it running. You'll have to take the piston off so you don't get grit everywhere. Check the bore for aluminum pick up, that would have to come out too. If you can measure the piston skirt and the bore if it has more than .006" clearance get a top end rebuild.

Gif Cool

_________________
FAA certified jet engine and aircraft technician
Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
40 years karting experience

Brandon Baldassi · Joined: 04 Apr 2010 Posts: 53

Walt,

It appears to be scored, however I can still feel the machined lines on the skirt. I will only be running it one more time before new piston/rod. Is there a special plier to remove the retaining clips on the piston, or will normal snap ring pliers do?

I will check clearance tomorrow.

Thanks for the replies,

Brandon

Walt Gifford · Posted: Sun Aug 12, 2012 8:39 pm Post subject:

you take the clip out with an awl or small screw driver and it ruins the clip. That's what the slot is for also raises a burr on the slot. You put the new one back in with duck bill pliers and your thumb nail. Don't use a KT100 clip, get the thicker IAME clips. You could probably leave the piston on if you wrap everything in rags.

I think you'll find the rod cost about $250 so unless there's a problem with it I polish the rod journals then install new pins and bearings. You can also polish the pins and reuse them if you turn the crank pin 90 degrees from where it was. Good luck finding a builder that'll save you money like that.

Gif Cool

_________________
FAA certified jet engine and aircraft technician
Nicholson Speedway class champion 2001
Yamaha KT100 Service Center
40 years karting experience

Tom Rickard · Joined: 01 Apr 2008 Posts: 56

It is definately an MRC, the last of the air-cooled ones.

The piston doesn't look like it's in bad nick in the first pic, but like Walt says, it does look like it's nipped a bit in the second pic, it is a bit hard to tell.

If it is just lightly smeared with aluminium, you can use sulfuric acid to remove the aluminium. (be sensible with safety precautions using acid, and don't let it drip onto the ports or crankcase aluminium)

If you are going to rev this motor above 19k, replace the conrod. The worn piston will only slow the motor down, a broken rod will likely destroy it.

john cochrane · Posted: Sat Jan 19, 2013 7:20 am Post subject: engine

all the coatings is off the piston, small scratches on ring, this piston has been in the engine a long time, guarantee the cylinder has taper, I'd guess it would take 2 piston sizes to clean up.. looks like it sucked debris in engine..

John Mulvihill · Posted: Sat Jan 19, 2013 9:49 am Post subject:

Hi Brandon,

Some more pics of the bore would help.
Movement of aluminum on the piston doesn't bother me too much unless its a huge amount or it has worked its way up to the ring and affected the ring seal.

When acid was mentioned, that was for use in cleaning up the bore where aluminum may have stuck to the surface. Don't use on the piston itself.

Where are you located?

John
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