First steps rejuvenating a rotted head.

[sgallaty]

So, I just pulled apart a motor that has a really nice bottom end, no metal flakes on the magnets and shifts crisply even when it's been sitting... 7500 miles on the motor.

The top end however is a mild travesty. mild rust on the cylinder head, and a heavy crust in one of the cylinders that could be burnt oil accumulation, mild scoring (or alum deposits) on the other cylinder.

So the question is, what approach in general should I take to rejuvenating this engine? How rough can I be with the cylinders to get the scale off in preparation for honing?

If there's mild rust and crap on the cylinder head, should I media blast it with the valves IN or out?

How do I judge if valve seats need to be recut?


What is the most effective and yet economical approach to take to rejuvenating what I have?

 

[Patches]

Your cylinders will need to be bored rather than honed more than likely. Without seeing anything it is hard to say, but you will probably need to got to one or two over rings and pistons and get the cylinder bored for them.

as far as your head is concerned, you need to remove the valves and inspect the sealing surface for the valves. It is probably pitted. It depends on how badly it is pitted. You may be able to get away with a lapping job, but more than likely they will need to be ground if it is rusted badly. I've seen ones pitted so badly that they were toast, and buying a new head and rocker off eBay for 80 bucks is a good alternative.

Remove the valves before you media blast. Get new valve seals too if you decide to rebuild.

While you are there you might as well clean up the head castings with a dermel and do a little porting.

My guess is this motor was sitting outside with no filters on it....? Was there any water in the cylinder(s)?

 

[sgallaty]

I assumed it was rust also, but it's not. It comes off the cylinder walls and the walls of the cylinder leave a smooth cast surface on it. Some of the material is plastic (in the technical sense)

There IS some surface rust near the exaust port that was stuck open.

ok so valves out, media blast the head and then see what we've got. I presume that's going to require a loupe or something.

 

[Patches]

Yep, you should pick up some lapping compound and sticks and see how it goes. If you have never done it before donamforum search, there is a good how to on the forum.

If you are using a very abrasive media I would steer clear of blasting the sealing surfaces, unless you are using something like soda.

Def take the valves out, replace the seals, lap the valves and give everything a good cleaning.

 

[sgallaty]

right - the sealing surfaces I am going to mask off with a couple layers of resistant material.

The heads are blissfully actually not too bad. It's the cylinders that are bad, and I don't know how bad yet. The pistons are probably trashed. The rings are totally jammed into them by what appears to be carbon.

This with 7500 miles on the bike too.

Here's the bad cylinder. The other cylinder has a very slight ring of sediment on it.

Closeup of the rot.

Here's the bad side of the head. As I said, not really that bad.

This is the other side of the head. I haven't actually cleaned it yet.

 

[Patches]

You're going to have to bore those cylinders and go to at least one over pistons and rings (.25mm larger).

I'd e very surprised if they cleaned up with just a flex hone.

 

[sgallaty]

Should I try some kind of rust removal first before doing that? Molasses water or something? I'd like to gentle off the rust before I go at it with abrasives.

EDIT:

I've drawn up some molasses water.

I washed the head first with running water, chose not to dishwasher it first (wife was watching =). and dropped it into the molasses water. I need to get more molasses, and I need to get the gallon jugs.

Used a typical 5-gallon bucket you get from a typical home improvement store.

Bear in mind that as the phosphoric acid acts, it is removed from the solution, so keeping the solution fresh (and periodically agitating it) is the optimal way to maintain the speed of this reactive treatment. Also the volume of reaction compared to the volume of solution matters.

I also lack a spring compressor for the valves - it was one of the things that didn't move with me on my exodus from the last place I lived.