mercruiser / cummins 120 hp engines

butty · 14 May 2009, 15:21

i have a coastline 6.5 with the mercruiser / cummins 120 hp engine in it, it is a wonderful boat and i could not fault it, but i seem to remember the engines are prone to issues, i have searched and read about them on here, but just wanted to confirm:

i have read that if the serial number of these engines starts with 88 then they are the line of engines that have had the initial issues resolved??

something to do with the waste gate on the turbo, i think?????

alt · 16 May 2009, 20:07

If your serial no. starts with 88 then I think the holed piston issue has been resolved (bad spray pattern I think)

However the wastegate issue still remains.

I think the issue (this was my knowledge from owning one) is that when the engine was marinised, the bearing on the arm of the wastegate... wasn't. It tended to seize up easily, which in turn restricted the wastegate from opening, when in turn led to an over boosted engine which... well... you know

I was recommended to use Mouse Milk (a high temp lube) on all the moving parts around the turbo, and check on a regular basis that the wastegate would function (push it with your hand)

I was lucky that I was on fresh water hence very little corrosion issues, but I still took the advise above and never had a problem.

Also make sure you're not over-pitching the prop, which leads to more stress on the engine which leads to the wastegate needing to function. Make sure your engine can rev to 4400RPM max. I think the max recommonded RPM is 4200, but the theory is that if you can rev to 4400RPM then you're not stressing the engine at 4200RPM, just go easy on the throttle stick - makes sense really.

Hope this helps

butty · 18 May 2009, 08:42

ok, thanks for that, shed a little bit of light on the issues.

will keep an eye on the waste gate and keep it lubed!!

the engine revs to about 4100 rpm max, so revving issue is ok.

thanks for reply.

alt · 18 May 2009, 10:01

Quote:

Originally Posted by butty

the engine revs to about 4100 rpm max, so revving issue is ok.

No, it's not. Read my post again.

You are over-propping your engine. The WOT RPM spec on that engine is 4200RPM, and for a stress free life it should be *able* to go to 4400RPM (Just don't put it past 4200RPM with the throttle)

You're causing your engine stress and will be another victim to that engine if you keep that up - your choice, just offering advise as an ex-owner of one

butty · 18 May 2009, 18:27

ok, my fault, mis read, was in a hurry.

i see what you are saying. thank you, will look into props now.

B36 · 09 June 2009, 21:38

The 1.7DTI even with 88 serial number is still prone to piston failure. The pistons and turbo were changed with a revised design from S/No: 8814000-on, however,the problem was never sorted. Its all linked to the waste gate. No body ever complains when the waste gate is stuck shut as the boat goes like a "bat out of hell" Combustion pressures rise and the weak spot in the pistion collapses.

Make a point in removing the heat shield around the turbo to check for rust on a regular basis, get the turbo cleaned/checked once a year by a specialist.

Another thing to check is the intercooler. Make sure the anodes are changed regulary as corrosion is a big problem on this part, also clean the intercooler every year, as they block up restricting performance.

Otherwise good motor

nik · 12 June 2009, 09:33

Quote:

Make a point in removing the heat shield around the turbo to check for rust on a regular basis, get the turbo cleaned/checked once a year by a specialist.

Is it possible to run the turbo without the heat shield?
Also, is there another better designed, maybe watercooled turbo, or one with a poppet type wastegate that will fit?

Nick.

B36 · 12 June 2009, 18:58

Hi Nik

Removing the heatshield is a bad idea, remember under high load that turbo will be glowing red hot! Not a good idea in an enclosed space.

Try to keep the heat shield dry, wet heat shield is the main cause of waste-gate failures

I would consult a turbo specialist about a water-cooled turbo, however, waste-gate could still cause problems?

Stu99 · 22 July 2009, 19:57

Hi

One of the pistons on my mercruiser/cummins 120 has just cracked. Does anyone have any experience if the manufacturer are willinging to provide the new piston parts for free?

Dirk Diggler · 22 July 2009, 20:08

Quote:

Originally Posted by Stu99

Hi

Does anyone have any experience if the manufacturer are willinging to provide the new piston parts for free?

Cookee · 23 July 2009, 07:25

Here you go: http://groups.yahoo.com/group/cummin...iser_120hp_DTI

B36 · 24 July 2009, 11:10

Quote:

Originally Posted by Stu99

Hi

One of the pistons on my mercruiser/cummins 120 has just cracked. Does anyone have any experience if the manufacturer are willinging to provide the new piston parts for free?

Hi Stu

Talk to Cummis concerning this, will depend on how old your engine is, but they have been replacing engines because of this failure, don't let them tell you otherwise.
Whats your engine serial number?

rdk12 · 13 February 2013, 10:04

RE 1.7 DTI mine has an 88 serial number.
I have recently bought a rib with this 120hp engine, we contacted Mercruiser to confirm the serial number mentioned in this post. I have today received an email from them saying that my engine serial number 88110661 has the redesigned oil nozzle spray pattern and revised pistons. They do say that the turbo over boost remains an issue and it’s been suggested that a boost gauge could assist with early warning, should the actuator arm start to meet resistance (seized waste gate) creating over boost.

This post shows someone’s rather rusty waste gate.
http://www.rib.net/forum/f36/picture...rbo-19538.html
Boat design is important, you wouldn’t want salt water coming in to the engine bay, if you accidentally reversed to fast...

The ribnet web site has been a great reference tool for me and I have deduced that as long as the engine is not overproped, the waste gate has an eye kept on it, it’s well maintained, it’s should be good for the recreational use it was intended for. My engine has been well maintained and benefits from a recently replacement turbo and assembly. I hope my post can assist others with their quest for knowledge. If I put my figures round the actuator arm that opens and closes the waste gate. I can feel it move when the engine is running under load and the throttle lever is moved back and forward gently. I’ll start a new tread with how I fitted a boost gauge and the results later.

Turbodiesel · 14 February 2013, 19:42

Horrible engines!!! They dont make them anymore, we have one in the workshop at the minute, just had a rebuild. Turbo waste gasket seized, and hole in the piston. Its been nothing but trouble since the rebuild!