Logo
FULL SITE MENU

90 hp with twisted crank

R

Roger G Trudeau

New member
I have a 90 hp that has a twisted crank, it is an early 90's engine. I am out of the country right now and I am having my brother inlaw try and find someone to fix it but not having any luck. The boat is near Boston if anyone knows where I could send him to get this fixed before i get home this summer I would greatly appreciate it. (unfortunately the Tohatsu dealer near us does not do internal engine work and some of the places contacted only want to do the job if they can do a complete rebuild. I really just want an r&r done on the crank so it can be re-alligned as the engine is a low hour unit that runs well despite this issue(it just has a limited top end) it was a fresh water used engine so it is not a rust bucket)
 
I just saw an ad for a guy selling two new crate Tohatsu '04 efi 90hp power heads complete with ignitions and fuel systems. Does anyone know if this would bolt up to my early '90's motor?

Thank you,
Roger
 
Roger G Trudeau said:
I just saw an ad for a guy selling two new crate Tohatsu '04 efi 90hp power heads complete with ignitions and fuel systems. Does anyone know if this would bolt up to my early '90's motor?

Thank you,
Roger
Click to expand...

Not possible. Tohatsu never had an EFI 90 and has never packaged powerheads with any other parts. IE A short block comes with nothing but block, crank and pistons. So, it would be used stuff or phony.
 
I was told he bought them from a technical college that had been offering a marine tech program but stopped and auctioned off their demo equipment. I tend to believe him as he runs a locall well know repair business. I did hear back from Tohatsu and the tech said the gaskets are the same but there are some different part numbers on other things so he was not sure if it would be a direct swap. the Tohatsu guy did not question the fact that I was asking about an '04 efi 90, though he was surprised that someone had a complete dressed assy.
Thanks, I will continue to look into this.
 
There is a remote possibility that those are TLDI (two-stroke, low-pressure, direct injection) powerheads, which are a type of FI, but not what we typically think of as EFI (or port injection), as used on some 4-strokes. Maybe for the MD90A or B. Tohatsu does not use year to designate motors, but rather model. And I agree with Elvin in that a Tohatsu powerhead comes only as the bare powerhead -- not with electronics or other stuff. If they are indeed complete with ECU and all systems (maybe assembled by the school into complete units?), they MIGHT bolt onto your unit. YMMV.
 
I am thinking maybe I should take the chance, worst case I can resell them or maybe find a newer lower end with a bad powerhead....unfortunately I am overseas right now and can't check for myself and unfortunately I am not finding anyone who knows for sure one way or the other....(could be the college got them as complete units and stripped off the lower units....)
Thanks for the input,
Roger

Just a thought but does anyone know if the crankshafts might be the same?
 
Last edited:
Nope. The crank kit for the MD90A TLDI is:
3T9000300M CRANKSHAFT ASSY $1,205.10
The crank kit for the MD90B is:
3T7000300M CRANKSHAFT ASSY. $1082.65
 
Thanks, do you know if the newer '04 crank would fit the older engine? I spent some time looking through parts lists for an '02 and a '03 and there seem to be enough difference that I don't think the whole powerhead would be a bolt on. The cranks look pretty much the same, with the exception of a different thrust bearing and lower seal, but it would be great to know if the newer style would work in the older engine....
 
There is no such thing as year in Tohatsu land. (Model/serial is everything). The MD90B might be a closer fit, but I couldn't say... I have no clue whether one could Frankenstein a TLDI power head onto a 90A frame.
 
I just did a quick search for Ackermans and don't see anything machine or outboard related. Can you give me any contact information on them?

I did find a shop in NH that will R and R the crank for me but I don't know a local shop that can reallign the crank. Anyone know of a New England shop that can reallign it?
 
It took 3 weeks instead of 4 days(10 hours labor and 2 days to have the shop reindex the crank) but had one low cylinder and screwed up advance plate upon return, been back there 2 weeks and I am not confident in what these guys can do anymore, be surprised if it runs for long when I get it back.
 
I did finally get the motor back with the cylinder fixed and it put together properly. it runs fine but still has low power and limted top speed. I can only run about 26kts top, with the previous 90hp motor on this boat, Aquasport Osprey 175 it would run 37 kts. I have read that the seals on the crankshaft that separate the crankcases can fail and would result in what I am seeing, I am wondering if anyone has any experience with this? I guess with a 30+ year old motor that sat unused for many years I should not be surprised that some seals dried up and failed. Maybe putting in the crank kit would have been a better solution than just reindexing my twisted crank....
 
Roger, If you're saying that you had the block apart, straightened out the crank, and reassembled using 30 year old seals... well, that was short-sighted. Yes, I would get a powerhead seal/gasket kit. There are no seals that "separate the crankcase", so I'm not sure what you're reffing to.
 
I am not sure what the seals are called as they are not shown except as part of the crankshaft assy. they would be what separate the crankcase space behind each cylinder where the crankshaft passes through. They did use new seals and gaskets on the ends of the crank and I don't seem to have any external leaks, what I am concerned about is not getting proper charging of the cyclinder due to leakage between the crankcase spaces....if that makes sense. If there are bearings between each cylinder on the crankshaft than the seals I am refering to would be part of them and could only be replaced by completely separating the crankshaft parts.....

Thanks
 
Ah... now I understand... I would not expect those cylinder-to-cylinder leakages to be too significant, especially at speed. At this point, I would check all the essentials involved with installation: transom height, trim, WOT RPM, and verify (to the nines) the link-and-sync. You may also need a different-pitch prop.
 
I have the cavitation plate even with the bottom of the boat, the linkages and timing are set by the book. I adjust trim by the gps speed to obtain max speed at a given rpm. I don't have a tach but figure that it maxes out at around 4krpm based on the speed it runs at. I started out with a 17" pitch prop and now have a 13.5 D X 15.7 Pitch, it gets the boat up on plane better but not fast it is still gutless, seems like with a 15.7 it should jump up on plane....I have not measured the max spped with the new prop as my brother inlaw changed props after I left last summer....one reason I did not feel it was overprop'd, please correct me if I am wrong, is that when running along at max speed 27kts +/- I could trim up the motor until the prop was losing grip and churning the water into foam and the motor rpm did not seem to pick up, I would have assumed that the motor rpm would spike once the prop became unloaded....
The carbs are fully opening and the timing plate is maxing out, I have tried adjusting the timing further while underway but there is no gain. I had been hoping to see a huge improvement after getting the crank reindexed but saw very little.
I know the exhaust passages in the powerhead are clear, is there a chance my exhaust could be restricted in the lower end?


Thanks
 
I would get a tach on it. Don't guess. If you are only at 4000, you need to reduce pitch at least 3 inches. If you are nearly 16 inches now, try a 12 pitch prop. I wouldn't expect to see the exhaust restricted in the LU, as the passages there are fairly generous. Every boat, even "identical" ones have different characteristics, and selecting a prop is always a bit of a crap shoot. It MUST be done by trial and error. You want WOT RPM to be as close to 5850 (without going over) as you can. That will dramatically improve the hole shot, and will get you into the torque range where the motor is making more power, so the boat can go faster. Anything below 5150 and the motor is lugging, and won't make it's rated power. If you trim up enough to ventilate, the motor should speed up until the ESG kicks in... but, at that point, you run the risk of damaging the water pump (and overheating). Depending on the hull design, you may still need to jack the motor up a half an inch or more.
 
Back
Top