View Full Version : 2000 Mercury 240EFI rebuild

06-20-10, 06:49 PM
Just bought a 2000 Speedster SK with the Mercury 240 EFI Jet Drive. I new it had an engine problem when I bought it but it turned out to be worse then I had hoped. There is no compression on the #4 cylinder and #6 has next to nothing. All the other cylinders have about 120lbs. When I pulled the head #4 piston is all beat up on top and on the edges and has also beat up the head some as well and of course the cylinder walls have some scoring. #6 is not that bad but you can see some wear on the cylinder walls.
Looks like I am going to have to do a total rebuild. I am familiar with working on engines but have never done anything with 2 cycle marine engines.
What would be the most cost effective means to rebuild this engine buy all the parts and farm out any machine shop work or buy a rebuilt engine and save me the time?
If I buy a rebuilt where would be the best place to purchase from and if I rebuild myself where would be the best place to purchase parts?

I have the engine service manual and looks like it would not be to bad to do but I see where you need the Digital Diagnostic terminal to prime the oil system or is there another way.

Thanks for the help and glad to be a new member of the forum

George Skinner

06-21-10, 01:55 PM

Sorry to hear about your problem. I bought a 2000 Isandia last June with the Mercury 240 EFI. Like you I knew there were engine problems...I recently finished rebuilding the engine and took it out for the FIRST time this last Saturday. Not saying it's difficult, I just had never done anyting like this before and I was taking my time gathering information. You might be in better shape than I was because my #6 cylinder had seized, broken the rod, and blew a hole in the piston AND a hole in the powerhead. There was also shrapnel all over the place (ie reeds and even pulse pump...this one still boggles me).I looked around a bit and got a remanufactured powerhead from Crowley Marine in Denver. They got my undressed remanufactured powerhead from OBR, but anyway, I got most of the other parts I needed from Crowley Marine after that. Me being a newbie to working on engines they were all very helpful. A guy named Dan there was able to help me make sure I was getting the correct parts.

The actual repair inlcuding the cost of the powerhead and some minor unnecessary parts was just under $5000. Which I don't think is too bad considering I the boat and trailer for $500.

As far as the oil system goes I assume that you are talking about the oil pump and not the reserve tank. I changed the worm bushing in the oil pump because it's plastic and I heard that they can wear out. I don't think that was my problem, but as long as I was there... As for priming the system. I think it does that when the key is turned on. If working properly it will definetly go to the reserve.

Hope some of this helps.


06-21-10, 02:39 PM
I have the engine service manual and looks like it would not be to bad to do but I see where you need the Digital Diagnostic terminal to prime the oil system or is there another way.

Where you do see that the DDT is required to prime the oil system? Chapter 3E of the manual discusses priming/bleeding and I don't see how the DDT is required. There are no electronic components or systems involved for the DDT to read.

06-21-10, 09:55 PM
Where you do see that the DDT is required to prime the oil system? Chapter 3E of the manual discusses priming/bleeding and I don't see how the DDT is required. There are no electronic components or systems involved for the DDT to read.

Thanks for pointing that out. I have found that the engine manual that was given to me with the boat is the incorrect year for the engine. I was looking in a manual dated December 2001. I have since downloaded a manual from the forum that better matches the engine.

06-22-10, 06:48 AM
Does anyone know where I can get a cylinder sleeve for this engine? I remember reading in a post that someone found one somewhere but I have not been able to locate that post again. Also where do you get oversize pistons and rings?


06-22-10, 09:38 AM
I had the same exact engine failure as you have with #4 seizing and #6 on its way out... Would bet any amount of money that it is the plastic oil pump gear with broken allen bolt that stopped pumping oil into the injection system.

I pulled my engine apart and bored it .030 over, new piston rebuild kit from ebay and all new bearings. Polish the crank depending on how bad it is. I took my time and marked all of the wires and vacume hoses. Bleed the motor after rebuilt (oil pump) and run double oil for the first tank (gallon with full tank plus oil injection system). I now have 4 tanks of fuel thru and it is running perfect...so far...

Spent $1,500 total. Would have gone .020 over but #4 needed at least .030... You can also just replace one or two pistons if on a short budget. However, probably would not save too much since you need all new bearings anyway...


06-22-10, 05:11 PM
Dave, thanks for the valuable information. That kind of cost I can manage. Do you remember who you bought the oversize piston kit from on Ebay?
I will check the oil pump gear and post what I find. I have to determine the cause so it does not happen to the rebuild.

06-22-10, 07:48 PM
Here is one of the auctions for $880...

http://cgi.ebay.com/ebaymotors/POWERHEAD-REBUILD-KIT-MERCURY-2-5-LITER-SPORT-JET-240HP-_W0QQcmdZViewItemQQhashZitem3ca234e1f5QQitemZ26041 9412469QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

I called him and spoke directly regarding the kit. He mentioned that they supply over 800 dealers or rebuilders around the country. Everything came in as planned with rings, bearings, etc. I think it totalled 1,100 including the main bearings $129 and a lube kit that was $40 and included sealant, thread locker, merc grease, etc. Also includes all the gaskets but you do need the base asket to install the powerhead back on the pump...

For the crank, you just want to make sure there is no scoring..Mine was ver clean and I just polished the surface with crocus cloth. If scored, I would have the machine shop polish it up... The most tricky part is getting the main caps on with a perfect fit...Need to check the seam as you torque to make sure that are matching perfectly. Also, the 90 degrees torque after the correct foot pounds is scary but seemed to work o.k... The only other issue is the oil pump worm gear that is probably broken.. You can get this from him as well and it is a harder derlin type plastic vs. the soft plastic original. I did use some JB weld on the alignment tips to hold with the screws provided.. You will see what I mean...Hard to put all hope for the engine on these little allen screws..

Good luck...Just take your time and read thru the service manual as you go.


06-24-10, 06:03 PM
Dave, you called it right. We tore the engine down today and the plastic oil pump gear was broken just like you predicted. We measured all the good piston bores and they all seem to measure out good, even slightly smaller then spec.
Do you know a good way to clean out the aluminum that has transferred from the piston to the cylinder on the bad cylinder? The manual say to use an acid solution such as "Tidy Bowl" but was wondering if there was anything else.
While it is apart does anyone know of anything else I should do before it is put back together.


06-24-10, 07:56 PM

Just a suggestion that you can bore out the one cylinder... They make the oversize pistons the same weight to allow this.. I don't know what you can use to remove the aluminum. I had bad scoring that it needed to go .030 over. If it doesn't need to be oversized you could hone and re-ring, etc. and save a lot of money. Also, make sure you get all of the aluminum out of the man bearings, intake housing, etc. In my motor there was aluminum everywhere.

For what it is worth, the new pump gear from the same guy I mentioned above seemed much stronger vs. the original. Also, the manual says to always replace the needle bearings.. You could probably just order these with the gasket kit. My guess the bearings on the bad piston rist pin are pretty bad. I did have some concern about the rod near the rist pin end on my motor. Seemed to have some heat marks but so far so good... I did replace all the bearings.


06-25-10, 11:32 AM
Dave where did you get your engine bored and honed?
I went to a local machine shop I have used before but they cannot bore this engine as there boring head and hone has to go completely through the cylinder and of course the cylinders in this engine have bottoms.
Talked to a couple of boat dealers and they send blocks out to some place in Pennsylvania to have them done with a 1 week turnaround. Unfortunately the pickup day is every Thursday and we missed it this week. Also the price for the work goes way up working through the dealers.

If anyone knows of someone within a few hours drive of Charles Town, WV that can do this engine let me know.


06-25-10, 07:35 PM
Found a machine shop near Hagerstown, MD that could take care of the engine work. Should have it back in about a week.
Is the plastic oil drive gear sold per each half? The online suppliers are showing a quantity of two required.
Dave did the rebuild kit include all the gaskets and seals for the entire engine other then the base gasket or are there some additional ones I will need to order?
Hopefully within the next few weeks it will be on the water.


06-25-10, 09:59 PM
Everything was includes from a gasket standpoint.. Make sure to keep the rist pin washers as these were not included with the new bearings... I almost threw them out. You will need the permatex sealant for the block and case surface. Actually, there was one gasket missing from the kit...The reed cage gasket that has three seperate rectangle holes...Not the one with the 6 reed cage holes...It was included.

For the gear, I purchased for $40 from the same company I listed earlier and it came with both halves, allen screws and square nuts. Also, I felt much more comfortable about the plastic material vs. original one... I don't know if I want to use the original (listed from Mercruiser) as I don't know if they upgraded or not. The aftermarket one was a derlin type plastic vs. an ATV Fender like material on the original.

Once I completed the rebuild, one hour for install and I was off and running. Just run the mixture in the oil and make sure to bleed the oil pump..Very important...


07-13-10, 03:12 PM

What was the name of the shop you used to have the boring work done?

I have the same issue. #6 piston melted. Prob a clogged injector from sitting.

07-13-10, 06:06 PM
The place I used was Berger Machine shop near Hagerstown, MD. They honed 4 cylinders and bored and honed 2 #4 went .030 over and #6 was .015 over. Just waiting for all the other parts to come in so I can get it back together. My problem was a broken plastic drive gear for the oil pump but I am going to check other things as I put it back together. I ordered the gear from the same person on Ebay that sells the rebuild kit. He has the gear made from a different type of plastic and has been selling it for 7 years with no problems.
Good luck with the repairs.


08-04-11, 06:28 PM
Believe it or not after rebuilding the engine last year I just now had the chance to get it into the water. Runs great but breaking in the engine so taking it a little easy. Oil level in oil tank seems to be going down so it appears the oil pump is working. Will keep an eye on the oil level the next few times out to be sure it is working. Running premix in the gas for engine break-in so not worried about the pump and gear yet.
Only problem I had was the speedometer is not working. Have to check the service manual to see how to check it. Anyone hear know what the most common thing to go wrong with the speedometer is?

Thanks to everyone here that helped with my questions. I could not have done it without all your help.

This is too fun, have to find a Jet Ski to go along with the boat.

09-10-11, 07:33 PM
Glad to hear you got it running! I hope everything last awhile for you! I been fight the port engine on my 97 Challenger 787 for the last year! (swap out the motor 3 times!) Never buy a motor from SBT! I think i'm gonna make the switch to the mercury v6 after i get it fix this last time. SBT has taken a year of my life away that i will never get back.

09-10-11, 07:41 PM
Had it out today and running great. The speedometer is still not working, works for a few seconds then stops working. I hope it last awhile too, these Mercury engines are expensive to rebuild.