Reusing Pistons to Save Money: The Benefits and Drawbacks
Rebuilding an engine on a Class 8 truck is a costly procedure. Depending on how extensive the repairs are, the parts alone can range from fifteen hundred to fifteen thousand dollars. One option for reducing the cost of an engine overhaul rebuild is to reuse the pistons. The pistons are typically the single most expensive part in a rebuild kit. Taking them out can make the kit affordable for nearly everyone's budget.
But this option might not be right for you. In this blog post we'll cover.
- Rebuild Kit Options
- Types of Pistons
- Factors to Determining What Kit to Buy
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Rebuild Kit Options for Your Diesel Engine
Just so we're all the same page, the common parts of any diesel engine rebuild kit are:
- A Complete Gasket Set
- Piston Rings
- Rod Bearings
- Main Bearings
Of course other items may be changed at the time of a rebuild such as your injectors, cylinder head, oil pump, etc., but they are not considered part of the rebuild kit. Highway and Heavy Parts offers two categories of kits to cover leaving pistons out or adding them to a rebuild kit. The two categories are "Re-ring Kits" and "Standard Rebuild Kits". The only difference between these two kits is if you get the pistons or not. Otherwise, all the included parts are the same. The price difference, however, can be over $1000. Again, pistons are the most expensive part of any rebuild kit.
If you're curious about the different types of rebuild kits, read our post, How to Choose an Engine Rebuild Kit!
Diesel Engine Piston Types
To be general the three types of pistons we regularly run into on Caterpillar, Cummins, and Detroit Diesels are either one piece aluminum, two piece steel and aluminum, or one piece steel.
The one piece aluminum piston is found on older and lower horsepower engines. On the good side, aluminum is light. The drawbacks include aluminum's lack of strength and thermal expansion.
Strength is fairly obvious. Aluminum is softer than steel and won't stand up to high cylinder pressures. Thermal expansion is when a part heats up it expands. Because aluminum and steel have different rates of thermal expansion, aluminum pistons are more likely to scrape the liner, or worse, seize altogether.
Two piece steel and aluminum pistons attempt to make the best of both worlds: the light weight aspect of a one piece aluminum piston and the durability of a steel piston. This is a great setup and very strong. It is found in a majority of the trucks on the road today. The drawback to this setup is still the aluminum skirt. The skirt is prone to scoring and will wear much faster than the steel crown.
One piece steel pistons, also referred to as monotherm, are the latest and greatest. These pistons are all steel, lightweight, and under normal loads, don't show any wear, even at the million mile mark. Many competition engine builders have switched to this style of piston for every engine they build.
So, those are the diesel engine piston options you'll find in many rebuild kits. What you actually have, though, depends on the make, model and serial number of your engine.
Want to know more about pistons? You can read our blog to learn how APR rings work
Factors the Determine What Kind of Diesel Engine Rebuild Kit You Buy
Now, how to decide between re-using or buying new pistons. Please take all of these factors into consideration together, picking and choosing won't tell the entire story. Here's what to consider:
1. Why are you rebuilding your engine?
If you had a major failure, overheat or damaged your pistons in any way, change them. Don't ask questions, just do it. If you're fixing power loss, blow-by, or leaks, a re-ring kit may save you some money.
2. How many miles are on your engine?
If you're at 650,000 miles or below and you had a failure that didn't damage any pistons, a re-ring kit is all you need.
If you're at the million-mile mark and you're rebuilding your engine due to power loss or blow-by, a re-ring kit is usually all you need. That is if you have either a two piece piston or a one piece steel. If you have a one piece aluminum piston, change them. Re-Ring kits for the two piece piston include the aluminum skirt so the only piece to reuse is the steel crown.
Many repair shops—the guys who build engines every day—reuse pistons on more than half of their rebuilds. Here's another secret: many of the OEM manufacturers also reuse the pistons in their overhaul kits. It's not as unheard of as you may think.
3. How long do you intend on keeping your engine?
If you're going to fix and ditch your engine, don't put more money in it than necessary. A re-ring kit will do the job. If you just put on a million miles and want to put on another worry-free million, then a standard kit with pistons is a good way to. Having 2 years of warranty with unlimited mileage on your rebuild is something that can help you sleep at night.
4. How much money do you have to put towards the rebuild?
If you don't have the extra money to put towards a rebuild, buying a re-ring kit may be your only option. Our staff will always try to help guide our customers on what's the best way to get out of a tough situation.
5. What application do you use the engine for?
An over-the-road truck pulling 40-60 thousand pounds has a much easier life than a gravel train pulling close to 160,000 pounds. A dump truck driving around a sandy gravel pit all day has a much different life than a Gen-set sitting outside of a hospital. The harsher the environment the more you should look at spending the additional money for new pistons. For heavy hauling and rough service, a standard kit with pistons is the way to go.
So to sum it up, each situation is different and needs to be looked at as such. Many diesel owners are not used to the longevity of the newer style pistons in today's engines. When we speak with them, they haven't even considered a re-ring kit. But, when money's a factor (and it almost always is), HHP can help save you some!
Have more questions about your diesel engine? Our ASE Certified Technicians are here to help! Call us at 844-215-3406, or request a quote online!
Originally posted April 25, 2017; Edited December 11, 2019