2.5 Mercury build

[wired247]

I am turning my late 2.0/150 into a 2.5 liter motor. Parts wise theres not a lot of difference between the two. Pistons and block. Heres a pic of the bore difference. Ports in the block are completely different but you get the idea.

Thats about it. In the late 2.0 motors the 150 carbs even use the same castings as the 200 HP 2.5's but with different jetting. The late 2.0's have 4 petal rubberized reed cages, 225 tuners and other good stuff. I picked up a really nice 1994 vintage 2.5 liter 200 HP block from a guy over on the Checkmate forum for $300 that had wasted a crank rod bearing. This is going to be a 7000 RPM budget build using mostly OEM equipment including the original pistons that came with the block and pistons and with parts from my 150 I should be able to build a 230-240 HP 7000 RPM max motor. The bores were near virgin in 5 holes but one had a little scoring so I'm getting that one bored .015" over. I will be adding Chris Carson Reeds, rejetted WMV carbs, a 16 amp charging system and a really obnoxiously loud exhaust system. I'm shooting for 80 MPH at 7000 with a 26 pitch prop. Should be easy

I sent the block over to Jim Rucks machine shop in Wisconsin and had him port the block to 225 Pro Max specs. The ports stayed about the same as before but Jim opened up the exhaust chest and contoured it to flow better. Jim also cut the rod slots to open up flow to the boost ports. Total bill for Jims porting was under $400 and I consider it a bargain and well worth it. That included straightening the cylinders a bit and finish honing.

Heres a shot of the opened up extended rod relief.

From the cylinder..

Exhaust chest

I'll be walking through the rebuilding and assembly stuff in the next few weeks up the the point where it runs in the water.

 

[1FASTLASER]

Re: 2.5 Mercury build

This is exactly what I am looking for.

 

[wired247]

Re: 2.5 Mercury build

I just dropped the front half of the motor at the machinist to get the face milled down .040". Opening up the rod slots created more volume in the crankcase which is exactly what you don't want. This will make up most of that lost volume and keep the air and fuel moving quickly. Rod slot opening is viewed by some as the spawn of the devil and by others as the greatest thing since wet *****.

I'm trying to keep the overall cost of the 2.0 liter 150 HP to 2.5 liter 240 HP ish conversion down to around $1500 or less. Actually it will quite a bit less as I was able to sell the 2.0/150 block for a few hundred to offset the cost of the 2.5 stuff. My 2.0 parts such as the rods and crank were pristine which helps. It could have been quite a bit less but I elected to go with new high strength rod bolts, metal caged bearings and new wrist pin bearings and solid motor mounts. Admitedly I got a real good deal on the block but that just shows there are deals out there. I feel comfortable with 7000 RPM and Mercury cast pistons. I wouldnt feel comfortable with 7001 RPM and Merc cast pistons.

 

[wired247]

Re: 2.5 Mercury build

Here I am last night opening up the 2 piece adapter. This is a steel sleeve motor and I will be spending most of my time under 4000 RPM so I did not want to use one of the hi perf one piece motor adapters or dry stack it. I did have to open up the adapter plate to match Jims porting work on the block though. Ten minutes on the mill.

Tonight I will be installing solid motor mounts. Still waiting on one OEM .015" piston and the rest of the stuff that I ordered from Chris Carson. I'll be taking a road trip to get the block bored on the one hole early next week . Then its game on for putting it all back together.

 

[1FASTLASER]

Re: 2.5 Mercury build

U ain't back with the block yet? Lol .... Seriously though this is the kind of motor I want strapped on the Laser. It's light the right hp and turning 7000 will get me where I wanna be

 

[wired247]

Re: 2.5 Mercury build

I got the solid motor mounts in today.Later this winter I will put a Seastar Pro hydraulic steering unit on the motor . Right now the boat is a real ***** to drive over 65 or so MPH. With the solid motor mounts and hydraulic steering it should be able to stay on the pad a lot easier.

I am using the tuner that came with this motor . I say its a 2.0/150 but its really not. Its a 105 HP Jet pump motor that I installed a prop lower on. Not too many differences between the two powerheads except that the jet 105 comes with the same tuner that the 225 Pro Max motors came with. Bonus.

I havent quite decided if I will drill the mid section or not. If I do it will be two one inch holes at the bottom of the mid section. I will not be installing the mid section liner though.

 

[1FASTLASER]

Re: 2.5 Mercury build

Is there any advantage to leaving the liner out? Also u stated that the tuner is essentially the same as the 225 Pro Max. Would u say that tuner is better for the topend?

 

[wired247]

Re: 2.5 Mercury build

Its better than the normal 150 tuner thats for sure. Those 135/150 tuners are worthless. The one I have is about an inch longer than the usual 2.4/2.5 hipo tuner but in that length range it would take that princess who got peed on to tell the difference between the two. Advantage to leaving the liner out? Sure. Its a lot louder. Thats about it. I had a 260 on there before with a factory drilled bass mid section and I really miss that throaty roar.

Those late 2.0 105's had a lot of the good parts like big bore carbs and the good tuner and good 4 petal rubber cage reeds. After removing the rev limiter, oil injection and idle stabilizer and shaving the heads to 28 cc and I could pull up to 7000 with the 105/150. That was with a 17 pitch prop. With the 240ish powerhead it should do the same with a 26 pitch but with a super strong mid range the 105/150 lacked.

 

[bajaunderground]

Re: 2.5 Mercury build

IMPRESSIVE! I had an older 2.4L 200 Blackmax rebuilt (it had the chrome lined cylinders, so no way to increase bore w/o liners). Almost wen that route, but decided against due to budget and time. Those 2.5L are sweet (almost unlimited HP, too a point?). The guy that rebuilt mine had one that raced in their hydrofoil that would spin upto 13,000rpms...of course it had all the high-end goodies! I was happy running 65MPH (gps) in a 'family boat'! Is that a Checkmate I see in the picture? What model? Starliner LD? (I forget which models had the pad?)

~Brett

 

[wired247]

Re: 2.5 Mercury build

Good eye. 1981 Checkmate Enticer. My dad bought it new in 1981 the same week I got my drivers license and Ive been dragging that boat around for 32 years. I gutted it and put a beefier transom and all new interior wood and upholstery a couple of years ago. New everything else too come to think of it.

 

[1FASTLASER]

Re: 2.5 Mercury build

Quick question Wired. You stated you would be ok with Merc cast pistons to 7000...not..7001. Knowing it would add a few more $'s and the posibity of running 6500+ a lot of its life would you just go with forged? Is so what brand would you suggest?

 

[wired247]

Re: 2.5 Mercury build

Quick question Wired. You stated you would be ok with Merc cast pistons to 7000...not..7001. Knowing it would add a few more $'s and the posibity of running 6500+ a lot of its life would you just go with forged? Is so what brand would you suggest?

Most pistons made for the 2.5 are cast. Most OEM pistons are cast and those are good for up to 7K. Not for hours at a time but for most uses. I want a boat that will go 80 MPH but that doesnt mean its going to do that for very long. 98% of the time I'll be under 6500. There are forged pistons for the 2.5. Wiseco makes some but, like a lot of people, Ive never had good luck with anything from Wiseco and for a sub 7K motor I'd prefer OEM Merc pistons. The ring locating pins tend to fall out of the Wisecos and their expansion rate require a lot of clearance to work well. Wizard pistons would be the best for a high RPM but they are somewhere around $1200 a set and are way overkill for what I'm doing. If I was going to build a race motor it wouldnt be a steel sleeve carb'd small rod motor. For under 7K the Mercury pistons are more than adequate. I'm in a odd situation though. The 200 EFI block I am using was used for less than 10 years before it wasted a rod bearing and lightly scored one cylinder ( probably due to a clogged injector ) and 5 of the holes had almost no wear. If I had to bore more than one hole I would have bored them all and likely used Vertex pistons. After this motor is all together I will probably run it for a few years and pick up a few 260 parts and a Brucato ECU and build a steel sleeve 260 clone with Vertex 225 PM pistons and a 260 injection front half and air horn and some race duty rods to make a 8K motor. That is IF I can get my hull to handle well even at 80 MPH. If the hydraulic steering does the trick and keeps the motor stable at high speed I'll move forward with picking the parts up. Fastest Ive had it was 77 MPH and that was fighting some pretty massive chine walk. If not I'll just leave the motor as is.

 

[1FASTLASER]

Re: 2.5 Mercury build

Thanks for the explanation. Man I didn't know the Wizards where that dang high. I have heard about a lot of failures with the Weiscoes plus if the machinist doesn't know what he is doing ur screwed before your ever fire the engine for the first time. And Marhl's top pinned ain't cheap neither. So when I build mine looks like Merc OEM is goona do me just fine.

 

[wired247]

Re: 2.5 Mercury build

Just before Jim Ruck retired I spent a good bit of time with him on the phone discussing this build , the porting etc. His opinion on top pinning is that it weakens the piston considerably and that the way some builders do the work does more harm than good. He also thought the Wiseco's were garbage. Thats just one mans opinion but Jim Rucks opinion carries a lot of weight to me. Ive built quite a few motors with the vertex pistons and for a fresh build I'd go with those for a mildly hopped up fishing motor. Only off the shelf top pinned piston that I know of that are the Wizards and if were building a nikasil race motor I'd probably go that route but not for what I'm doing.

 

[1FASTLASER]

Re: 2.5 Mercury build

Yeah Jim is one of the top dogs out there. Hated he retired but I hear the man that took his place has been WELL trained

 

[1FASTLASER]

Re: 2.5 Mercury build

Lemme ask u this Wired. You may have chimed in on my post on the other board. I don't remember if u did. How do you feel about balancing the rotatig assembly and going with a light weight flywheel. I feel like it will be a plus others say don't o the flywheel.

 

[wired247]

Re: 2.5 Mercury build

Lemme ask u this Wired. You may have chimed in on my post on the other board. I don't remember if u did. How do you feel about balancing the rotatig assembly and going with a light weight flywheel. I feel like it will be a plus others say don't o the flywheel.

It really depends on the RPM range you are shooting for. Under 7 K with rods from the same motor and pistons from the same motor I think its not really necessary, In this build I am using like rods and pistons from the same motor. I am adding one piston and it will be weight balanced with the piston being removed. For a higher RPM motor, it is necessary to balance the assembly. If I was using new race rods and lightweight forgings I'd be sending all this stuff out for a balance job as I'd be twisting it up pretty high.

On the flywheel if you are spinning it over 7K you'll want a light flywheel. At the minimum over 6K it's worth getting rid of the 40 amp charging system and using a 16 amp system. Even the cast 16 amp cast flywheel is a lot lighter than the 40 amp and the magnetic drag is considerably less.

 

[wired247]

Re: 2.5 Mercury build

Did a lot of hair pulling today. My new Mercury .015" over piston came in yesterday and I was getting my stuff ready to take to the shop to get that one whole bored. I threw the new piston on the scale and it was a full ounce LIGHTER than the others. 29 grams Started thinking what the hell am I going to do to get this thing to balance. The rest are all 995-1001 grams assembled ( without rod bearings ) and this one was in the 960's. I didnt want to go hogging metal out of the pistons. Started looking at lightweight wrist pins which would have got it in range but its kind of a goofy way to do it and expensive. Then I remembered I had a junk drawer with 30 or so rods in it from different blocks I have cannibalized over the years . Some were junk and most were too light. I did have a set from a '92 150 that were all on the heavy side and one weighed in at 376 grams which was about 25 grams heavier than any of the others in my new build. Total weight on the with the new piston and heavy rod assembly came in at 997 which is in range of what the others are at and damn near the same as what the original rod and piston assembly for that hole was. Not the best way to go but it will work. Off to the machinist this week and with any luck I'll be assembling next weekend and posting more build pics.

 

[Dukedog]

Re: 2.5 Mercury build

That's something that's pretty "normal" for Merc/Mariner. Even in tha Hi Performance stuff. It will be fine in a basically "stock motor.......When they are built, its "whatever is in tha bin" when tha parts are gathered up. Pretty much same with replacement parts....

 

[wired247]

Re: 2.5 Mercury build

Got this back from the machine shop today. I had the manifold mating surface milled down .040" . With a 2 cycle engine anything you can do to reduce crancase volume will be rewarded with faster throttle response and better air and fuel mixing. .050" is about the most you can get away with without requiring reed cage mods or possibly smacking the rods with the reeds. .040" is a safe margin. $90 for the labor on this job and I'm still way under the $1500 budget. As stated before this is a sub 7K build so I am fine with the 4 petal rubberized cages . If I were going over 7K I'd be looking for a 7 petal front half and probably going with a 5 petal rubberized cage reed set. That and the fuel injection are for next years bonus. Off to the other machinist tomorrow to get one hole bored. now that I am reasonably content with the reciprocating assy balance.