Piston and ring help

[SySteMAtiC72]

Well I'm on my second rebuild of 3 and I'm not happy with what I see inside the bores of both heads. On the exhaust sides I'm seeing heavy scratches up and down the bores. I would say that they are a couple grand deep.
I'm wondering what my options are. I will say that I do have a machine shop so I can bore them myself but is there more I need to know? Are they chromed?

[gixxer6]

What sled? 

Have you done a compression test?

[SySteMAtiC72]

It's an 78 Invader 440. I tried doing a compression check last winter when it died but I don't remember the exact numbers. Plus I couldn't get it started to warm up the engine so I pretty much chalked it up as a waste of time.

[rminier]

 The cylinders were chrome plated from the factory....that doesn't mean a previous owner may have had the cylinders bored and an iron sleeve installed. But you should be able to see the difference between a shiny chrome bore, or a dull iron sleeve.
 It is pretty subjective to say yay or nay about your current cylinders, if they are still the original chrome plated. They can be run successfully with minor scratches....usually any scratch large enough to be felt with a fingernail is questionable to run. Minor scratches are still useable if you have good, equal compression on both cylinders.
 One option is to buy a cast iron liner to install in the cylinder....the liners are kinda expensive, then you have the machine work to install it in the cylinder.
 The original cylinders can be rechromed to like new condition....a couple big companies that are known in the snowmobile world are "Millenium Technologies" or "U S Chrome"....there are others, also.....but that costs a big chunk of change.....I haven't had any cylinders re-chromed for a long time, but I suspect you are looking at 150 to 200 bucks per cylinder???
 I still see used cylinders on Ebay from time to time....of course...."Buyer Beware" buying stuff on Ebay.
 Perhaps someone on "KawasakiTrax" has some decent used cylinders they would sell.
 There are a variety of opinions on honing chrome lined cylinders....if they aren't too bad, I would be tempted to try a light honing with the proper sized ball-type hone.
 You can search on this site under "honing" or "hone" for some additional info.

[Interceptor398]

Invader cylinders are pretty easy to find.  There are even a few NOS ones left.

[gixxer6]

Even a cold compression test should tell you if they're completely shot or not. 

Like rminier said, they came stock with chrome bores.  I have had good success LIGHTLY honing the chrome.  Here's how I would proceed:

1.  Do a compression test, if good, stop here and run it. 
2.  Remove top end and inspect
3.  Hone or replace cylinders with good used
4.  Replace pistons and rings
5.  Determine what caused the failure

[rminier]

 Along with this subject of chrome plated bores, I had to "Google" Nikasil.....the material that the sled manufacturers moved to sometime in the 90's that was even better than chrome.
 If you check out the "Wikipedia" entry under Nikasil, there are a few paragraphs that are pretty interesting to read....even used in Formula 1 and Indy car engines. 
  SySteMAtiC72, I see you're from Ft. Wayne.....I grew up on a small farm about 20 miles North, near the little town of Avilla.....

[SySteMAtiC72]

This engine died about a half mile out in a field last year due to the fuel pump not getting a strong enough pulse.

The bores check at 2.667 so I know they haven't been bored. As far as the compression goes I think they were around 120ish while pull starting but I don't remember to be exact. They aren't shot. I know I could probably hone them and they would work.  I prefer to do the job once rather than risk trouble down the road and wasting money on more head gaskets. However, I have 3 of them I am working on so I am trying to keep it affordable. I'm still at odds but I'll probably order a hone when I get to work tomorrow and rework them next week sometime when a machine opens up.

I for sure want new rings. Is there any identifying marks on the pistons that anyone knows of so I can verify if they are OEM. When I was searching for rings everything I found only matched their pistons.

Also when I was indicating flatness of the heads the spark plug side was milled .04 less than the other head. Why would someone want to put the plug .04 closer to the piston but not the other? I'm gonna turn a spacer at work unless someone can explain the benefit of it.

Thanks for the help guys and nice to meet you rminier.

[Interceptor398]

.04 less could be a head that has been turned down to raise compression.  Are you able to post pictures of them?

[SySteMAtiC72]

As you can see the top head has the top milled off where the spark plug goes.

[gixxer6]

If it were me, I'd replace them with a stock unmodified set.  Heads are very easy to find and are fairly cheap. 

[Interceptor398]

That one is a puzzle to me, for what reason would someone do that??