Mercruiser Cummins 1.7 DTI 120 HP Turbodiesel Pistons

[Daithi]

I know this may not be a well known engine but I'm hoping someone on here can share experience of these engines rebuilt with non-Mercruiser pistons. Merc/Cummins pistons clock in at over $250 each (with rings extra) putting a set of pistons and a head gasket around $2000 before Labour

I came across at least two of these rebuilt engines in recent years. Both had used Isuzu auto pistons as it’s an Isuzu block but they have a slightly different combustion chamber in the piston crown. I don’t know how they fared long term.

So while no one is advertising about using non-Mercruiser parts they are getting used. I'd really like to hear if anyone has any information on using alternate pistons especially as the outrageously priced Mercruiser ones seem to fail anyway. I was careful to buy an engine with the modified-against-pistons-melting serial numbers (88+) but that doesn't guarantee a trouble free life as the wastegate seizing can cause similar problems as I suspect I have a cracked piston.

Many thanks for at least reading this post.

 

[scoflaw]

No info on exactly what your asking, but I have dealt with piston manufactures before, and they can make you anything you want in any material to any spec for about $700 a set. I've had good luck with Diamond.

 

[alldodge]

No experience with this motor but have rebuilt several diesels and to date have never had issues with not using OEM pistons. Not saying there any better then others, but have found no issue. Should not be an issue using others.

Did find there are 3 different piston "grades" from $303 to $310 each
882692001 - A
882693001 - B
882694001 - C

No idea why there are different grades even mean

Have not had any pistons made special as scoflaw mentioned, but sounds like that might be the way to go if they can find the specs to make them.

 

[Bondo]

Both had used Isuzu auto pistons as it’s an Isuzu block but they have a slightly different combustion chamber in the piston crown.

Ayuh,..... Welcome Aboard,.... I too, know nothing about yer motor,...... But,.....

That's an Isuzu block,.... Isn't that same block/ motor used in Isuzu trucks, as diesel motors,..??

What I do know 'bout diesels, 'n gas motors is,.... the piston crowns are very different for a reason,....

 

[Daithi]

No info on exactly what your asking, but I have dealt with piston manufactures before, and they can make you anything you want in any material to any spec for about $700 a set. I've had good luck with Diamond.

Now that’s interesting because frankly I’d expected about $500 would cover a set of pistons and rings and was wondering whether Mercruiser were making them from titanium! Would you have a website please?

 

[Daithi]

No experience with this motor but have rebuilt several diesels and to date have never had issues with not using OEM pistons. Not saying there any better then others, but have found no issue. Should not be an issue using others.

Did find there are 3 different piston "grades" from $303 to $310 each
882692001 - A
882693001 - B
882694001 - C

No idea why there are different grades even mean

Have not had any pistons made special as scoflaw mentioned, but sounds like that might be the way to go if they can find the specs to make them.

I’ve rebuilt a few engines myself and never baulked at using pattern parts. I’ve often found so called pattern parts are from the same OEM as used by the manufacturers. The original pistons are in fact made by Isuzu who make the block which is why I’m surprised I’m struggling to find them. Indeed my local engine rebuild experts failed to match them either and these guys pride themselves on matching even vintage parts with modern similar parts and modifying if required.

Youre correct on the three grades and my authorized Mercruiser dealer when quoting the pistons was unable to explain the grade thing. I assumed it was for standard bore, first rebore, etc. He was a bit embarrassed at the prices as he thought it might be for a set of four!

 

[alldodge]

Just guessing but the different grades may have something to do with if block or head need to be shaved. Most all diesels never get bored over size because the compression will increase more. They either use replaceable sleeves or they are bored out and a press fit sleeve is reinstalled. If head or block need to be shaved, they need to bring the compression height back into spec

 

[Daithi]

Many thanks to all of your for your prompt responses and attempts to assist. I've been on this forum since 2004 but had to get a new ID a couple of times through losing my email addresses with changing jobs!:joyous:

Anyway, in case it´s of any help to anyone else coming here looking for information, I´ve had the engine stripped and measured a piston best I could. Diagram attached.

Then I used that information, the engine number and block type -Isuzu as Bondo said - specifically an Isuzu 4EE2 to identify the closest possible matches from ARCO.

The 4EE2 is 10mm longer while the 4EE2 DTi is a match in all the main areas although the combustion chamber is a slightly different shape to the piston from the engine.

This may be the one I believe has been commonly used in rebuilds but can´t find any verification and ARCO can't assist except to say it is designed for this block.

I don´t know what the latest Mercruiser pistons look like but the ones from the engine are Isuzu branded as you can see from the photos.

My engine doesn´t appear to have ever been previously stripped so I´m assuming these are the OEM originals. ​

As Alldodge said Mercruiser offer three grades but the Workshop manual shows all three are identical diameters and my Mercruiser dealer can´t currently explain the difference. So the Alldodge suggestion to maintain compression ratio after a head skim is a good bet.
At over $300 each -plus rings, it´s not hard to see why people have used alternative auto pistons.

What I'd like to know is if anyone can help with exactly what alternative pistons have worked in this engine.

The OEM pistons all seem to crack or hole anyway despite modifications to the engine design early in its life, particularly if the Wastegate seizes closed or if the engine is over-propped.

Be advised that a prop that was right when the boat was new can turn into an over-propped situation if the hull gets heavier through water absorption, additional equipment or a change of use, e.g. carrying divers instead of fishermen or family.

These engines, unusually for a marinized auto/truck engine are boosted from typically around 80/90 BHP up to 120 for marine use. On land it's an immensely popular block used in cars, vans and a lot of the refrigerated units you see on trucks and shipping containers. The Mercruiser/cummins 120 DTI runs a closed pressurised cooling system with a heat exchanger, a bigger turbo and an intercooler. Normally manufacturers de-tune engines for marine use so while this engine has great power-to-weight and simply amazing fuel economy, it spits the dummy rather expensively on entering an over propped or over boosted situation.

 

[Scott Danforth]

the difference is not the bores, those are all the same. on a diesel, the differnce is the crown of the piston. this is where the magic is on a diesel engine. combine the piston crown with multiple fueling events during the combustion process and you control everything from torque, to economy to emissions. this is where the fuel guys and the combustion engineers get all star-eyed.

the differences in the pistons is the compression height, piston height and skirt, however could also be ceramic coated crown or a thicker head (not covered in the specs)

over-proping increases combustion temperature significanly and so does over-fuelling the 1.7 was marginal on heat exchanger size, and any lack of HX maintenance would spike the temps. this would lead to the big ole hole in the middle of the piston as the aluminum melted

 

[QBhoy]

Hi. These engines aren’t great in boats. Great wee things when running, if not a little coarse...but very economical. Quite popular over here in the U.K. as an alternative to the 3.0 petrol and usually run quicker, believe it or not.....anyway...
these engines are indeed Isuzu made and are widely used in many many cars over here. Most popular of which is the Vauxhall diesel cars of the late 90’s and early 2000’s. You won’t be surprised to learn or remember that Vauxhall are just a U.K. branch of GM !
if you guys have any small compact cars over there with a 1.7 turbo Diesel engine....very likely it’s the same engine. It was sold out to many manufactures in Europe to use in small diesel cars.

 

[QBhoy]

Also worth noting that although these wee engines are strong enough in a car.....what tended to happen over here is that in the marine application, people ran them on red (tax free non road vehicle) diesel. Because this is often stored in a poor manner in damp big boat yard tanks and usually full of water, when running these wee engines on this and poor filtration, they just could cope with any sort of moisture in there at all. Not like the big commercial based Volvo Penta lumps.
Oh and timing gear belt failures was also a big one too.

 

[QBhoy]

Hundreds of them for sale over here. Cheap as chips too !

 

[Daithi]

Thanks to Scott Danforth for the input and for sure it's a highly stressed diesel at 60BHP/Litre so everything has to work right and that's after it has been correctly set up. The wastegate seizing seems to be the fastest kiss of death while clogged intercoolers or overpropping or boats getting heavier with water logging or hull growth or additional weight will all kill it too. I operate on the SW coast of Ireland so at least North Atlantic water temps are low at the best of times which helps!

QBhoy you're right they're a popular auto engine in Europe. This Cummins badged Mercruiser was made in Poland. It is however a rather distant cousin from the Astra engine you pictured even though it shares the 4EE2 Isuzu block. After that the starter, timing belt and covers appear to be about all they have in common. It has a bigger Turbo (Mitsubishi TF035), closed pressurised cooling system with heat exchanger and an Intercooler - all to get more power than the car/van version. It also has it's own Cylinder head running DOHCs using bucket and shim clearance adjustment. The pistons are also different and they were a very weak spot in the early units.
Unlike most marinised engines, Mercruiser boosted output rather than the traditional derating.
That Isuzu block is incredibly common not just for auto use as you point out but also in Refrigeration units on Trucks and Containers but in those applications, it produces only about 70-90 BHP.
It would take a lot of parts to get the engine you pictured working on the end of an Alpha One - Unfortunately!
I'm just amazed that its proving nearly impossible to find the exact Isuzu branded pistons but I'm learning a lot about these engines!
I'm persisting because it is a fantastic engine with lots of power for its weight and phenomenal fuel consumption. For a diesel, it's reasonably quiet and has proven very capable in nasty conditions.

 

[QBhoy]

Ah. That’s a bugger. Thought they would share more parts. Back to the drawing board !