Rebuild

[JimT]

To expand on the others:

Seems the newer the engine model, the sooner it typically needs a rebuild. Some of this is by design (ie: engineering trade-offs, emissions, cost savings) and some of this is because of increasingly bad maintenance practices. If I remember correctly from Rawze's Book (see links above) the cm2350's fall into the 500-700k range, on average. Now, that will vary depending on maintenance and abuse history.

As for signs that a rebuild is needed. Excessive blow-by, oil consumption over 1 gallon about every 4,000 miles, signs of significant metal debris in the system (metal having flaked off of cams/rockers, failed fuel pump, HIGH levels of iron in an oil sample, etc...), coolant in fuel, exhaust gasses entering coolant (excessive pressure/bubbles in coolant tank, results of coolant test strips), signs of bearing failure (such as high levels of copper and/or lead in an oil sample). Evidence of valve damage/malfunction. I'm sure there are others, I'm not an expert.

Often times it's a combination of things that require enough labor that a rebuild just makes sense at the time. Parts wear out eventually and it's usually more cost effective to do one larger job then multiple "smaller" jobs. For instance, I was burning a gallon of oil every 3k mi, had decent blow-by and discovered a bad lobe on my cam. For me it just made sense to do a full inframe instead of just replacing the cam and rockers.

As for cost. It might vary depending on exact parts needed. But you're looking at $15,000 for a new head, rebuild kit and typical odds and ends. If you have to replace other stuff it'll be higher. I spent $23,000 for the above mentioned parts AND a new fuel pump ($4k), new oil cooler, new cam ($2k) and rockers. As for typical shop labor, $5,000-$6,000 for a decent shop (not dealer) up to $8,000-$10,000 depending on extras and/or price gouging. These numbers are just meant to be a rough estimate and will vary based on your exact situation and needs.

Doing it yourself is NOT hard. BUT it does require certain specialty tools/equipment which could cost nearly as much as cheap shop labor to buy. Some might be borrowed or rented if you know the right people or certain tasks can be outsourced (such as counterboring the ledges for the liners). Simply put, it's probably more cost efficient for the normal person to schedule ahead of time a week or 2 of down time and pay a GOOD shop, like Mr. Hagg's place, to do the labor for you. If you have the equipment and basic skills then Quickserve has 99% of the information you need to do the job. The other 1% is available from people here.