Carbon???

[bikedelic]

Took my heads and cylinders off today. There is a large heavy carbon buildup on the front piston and hardly anything on the rear piston. What would cause the front to build up and rear to be almost spotless? 91 Evo, 47k miles.

Also, the rear plug was pretty fouled, the front, fairly normal.

[Dave63]

I'd suspect an intake leak at rear cylinder intake seal. If you were to compensate for the leak, the front would run slightly richer.

As well, I'd be curious as to the compression difference between the front and back, prior to taking it apart.

Why ARE you taking it apart?

[bikedelic]

Originally Posted by Dave63

I'd suspect an intake leak at rear cylinder intake seal. If you were to compensate for the leak, the front would run slightly richer.

As well, I'd be curious as to the compression difference between the front and back, prior to taking it apart.

Why ARE you taking it apart?

The base gaskets were leaking and the paint was flaking pretty bad so while I had the rocker boxes off I thought I would have a look at the pistons and cylinders and replace the base gaskets. I am also installing new pushrods, tappets and an EV27 cam.

I stripped the paint off cylinders today and I will strip heads later this weekend. I am going to leave the heads with the raw aluminum sand finish and redo the black on the jugs.

If you will recall from a previous post, I had a noise I thought was tappets.

[Dave63]

Originally Posted by bikedelic

The base gaskets were leaking and the paint was flaking pretty bad so while I had the rocker boxes off I thought I would have a look at the pistons and cylinders and replace the base gaskets. I am also installing new pushrods, tappets and an EV27 cam.

I stripped the paint off cylinders today and I will strip heads later this weekend. I am going to leave the heads with the raw aluminum sand finish and redo the black on the jugs.

If you will recall from a previous post, I had a noise I thought was tappets.

Ahhhhh. I forgot. Check to make sure the valve guids aren't all carboned up and/or worn too.

A chunk of carbon banging around in a cylinder can make a pretty funky noise too.....

[bikedelic]

Thanks Dave, I will check them before I put it all back together. I hope you had a great Thanksgiving.

[tussuck]

If you have the jugs off you may want to look at getting them honed and popping in a new set of rings.


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[Hunt/fish 365]

Originally Posted by tussuck

If you have the jugs off you may want to look at getting them honed and popping in a new set of rings.


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X2 With 47K and the fact you already have it apart you might as well freshen it up.

[bikedelic]

Can the jugs be honed (they look pretty good - very faint crosshatching still visable) without needing new/oversized pistons?

I still curious about the lack of carbon buildup on the rear piston too. Also still curious about why my rear plug is fouled and not the front plug.

[SCHMIDTYS]

The carbon buildup and fouled plug could also be caused from leaking valve seals, common Evo problem. Oil getting past the seal into the combustion chamber.
Installing new rings you'll want to hone the cylinders for a fresh cross hatch, helps the new rings break in. I use B-B hones (ball hones) instead of stone style hones.

[tussuck]

Correct on the honing... All they do is refresh the crosshatch so you can keep the same pistons. Just buy a set of new rings and you will be good to go. Very much worth the effort!


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