1968 Evinrude 40 hp Big Twin Overheating

[supagidget]

I have a 1968 Evinrude 40 hp Big Twin on a 1965 16ft Aluminum Boat. I bought the boat, motor and trailer, all original, as a package.

I had the carbs cleaned when I bought the boat and everything else looked fine.

I took the boat out one day and it overheated bad. Prior to overheating I was idling for 20-30 mins. My theory is that the old motors were not made to idle for long periods of time because they do not circulate a lot of water in idle, at least mine doesn't.

After overheating I had the impeller and head gasket replaced. The coils and condensers where checked and repaired as needed, apparently it was only firing on one cylinder at times.

The first time I got on the water after the impeller was replaced it overheated again. after about 10-15 min at a high idle (no wake zone) I opened her up. Just after she planed, at 1/2 throttle, she powered down and would not start.

Someone told me that I need to replace the powerhead and that it would cost $1,000.00. Is that what it should cost? Is it worth it?

Would a faulty gasket, say base gasket, cause the second overheat?

Is there something I should look into before replacing the powerhead?

Thanks for any help?

Ashley

 

[raczekp1]

Re: 1968 Evinrude 40 hp Big Twin Overheating

check compresion and after think about if there is a need to change powerhead.

you should do the head flatening becouse it can be warped-you can do this at auto repair shop,
and when head wil be flat, place new head gasket and try compresion test.

drop lower unit and atache garden chose and run some water and watch how water circulate.
look also at termostat

 

[lindy46]

Re: 1968 Evinrude 40 hp Big Twin Overheating

Did you ever check to see if water was spraying out the exhaust relief port on the back of the leg? Just because a new impeller was installed doesn't mean it was installed correctly.

 

[kfa4303]

Re: 1968 Evinrude 40 hp Big Twin Overheating

exactly. I'm thinking that the copper, water uptake pipe may not have been seated properly into the top of the water pump housing. Fairly common, but pretty major problem. It may also have become loose where it enters the power head. The fins of the impeller may have gotten turned around the wrong way too and/or broken down and become lodged in the uptake tube. The drive shaft impeller key may have also been lost, preventing the impeller from engaging the drive shaft. Did you/shop ever try to run the motor on muffs? If so, that could damage an impeller too. Theses old gals can't run on muffs they need to be run in a test tank with water filled up to about and inch or two below the exhaust port. Just some guesses..... Ditto on the garden hose test described above. As for the powerhead, compression is the key. If/when you can get decent compression again, almost everything else can be fixed/replaced (carb kit, points and condensers, etc...)

 

[dice_left]

Re: 1968 Evinrude 40 hp Big Twin Overheating

I had the same problem when I tried running my 35 BT without the breather cap on top open

 

[1946Zephyr]

Re: 1968 Evinrude 40 hp Big Twin Overheating

These old motors should be able to idle just fine, if the cooling system is functioning properly.

 

[kenmyfam]

Re: 1968 Evinrude 40 hp Big Twin Overheating

These old motors should be able to idle just fine, if the cooling system is functioning properly.

Agree. ^^
Do some basic checks and go from there. Sounds like the cooling system was never verified as functioning before being put into service.

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

I checked the compression last night. I had 105 psi in each cylander on a cold test and water was coming out of the exhaust the last day it overheated. So I think the impeller was properly installed. Could the thermastat be stuck closed preventing water from circulating around the head? I read that you should replace the thermostat and the pressure release valve after an overheat. Just looking at where my thermostat is I can tell it wasn't even checked.

As for the garden hose test to see where the water is ciurculating, after dreopping the lower unit where would I connect the hose and where I am looking for water circulating.

I have the original flush kit for the motor, so no muffs here. The guy I take my boat to is a genious with old johnsons and evinrudes. I just don't see how he could say I need a new powerhead without even looking at the motor after the second overheat.

I think he may want to play with his own motors instead of mine...

Ashley

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

One more thought on the t-stat issue...

I read some other forum posts about the t-stat and the water cooling system on my motor. It said when the t-stat is closed only a mist will come out of the exhaust but when it is open you will have a greater amount of water in the exhaust.

The motor also seems to cavatate a lot on plane.

The motor rarely if ever has more than a mist. I live in Florida and the water temp is currently 88.

Ashley

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

T stat replaced and no water came out of exhaust on test in tank. Dropped the lower unit. Garden hose test checked out. Attached hose to one intake tube and the water flowed thru perfectly. Started her up with the lower unit removed and the garden hose attached. Water leaked out of the spark plugs so I took the head off. Cylinders looked good one small score mark and a little carbon build up but otherwise okay. It appears as though the exhaust gasket is leaking. I am going to get the head decked, replace the exhaust garkets, head gasket, head cover gasket, put in new impeller, plate and housing. Let's see if that fixes things.

One question: The drive shaft stayed in the midsection when the lower unit was removed but I don't think it should have. Should I try to get it out?

 

[tx1961whaler]

Re: 1968 Evinrude 40 hp Big Twin Overheating

One question: The drive shaft stayed in the midsection when the lower unit was removed but I don't think it should have. Should I try to get it out?

How are you going to assemble the water pump without the drive shaft out? The impeller should have a key that should have prevented you from removing the lower uniit unless the drive shaft disconnected.

 

[kfa4303]

Re: 1968 Evinrude 40 hp Big Twin Overheating

I agree with tx1961whaler. I'm not sure how you could've done that :/ I would try to get the drive shaft off of the underside of the powerhead for starters. Then reinstall it in the lower end by removing the water pump housing and gasket. Be sure to keep and eye out for the impeller key it pretty tiny, but very important. Perhaps it's rattling around in the water pump housing? If you're lucky you may be able to get the drive shaft to seat properly in the pinion gear in the gear case, but I think you may have to open up the gear case to be sure. Ideally, when you drop the LU it should have the drive shaft and the lower shift rod coming out of it, while the copper water uptake tube stays in the exhaust housing, but anything is possible. In any event, make sure the driveshaft ends up in the LU before you try to reinstall it back on to the motor, and make sure the water uptake tube seats properly in the waterpump housing so water can get from the water pump to the power head, then reconnect the lower shift rod into the shift rod connector and that's it. Good luck. Keep us posted.

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

Just got head back from the machine shop. It was resurfaced, cleaned and all of the water passages/ports were blown out.

The drive shaft definitely did not come out with the lower unit and definitely should have. I have read a lot posts on how to separate the drive shaft when it is stuck to the crank shaft but I am afraid that I will damage the crank shaft when I try to remove the drive shaft.

Q1 Any expert advise on how to remove the drive shaft without injuring the crank shaft?

Q2 Other than leaky exhaust gaskets, what could cause water to enter the upper cylinder through the exhaust port?

Can't wait until the weekend to get working on her again.

~Ashley

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

Updated my old gals progress...

Last weekend was not real eventful but we were successful in removing the exhaust housing, 6 of the 16 bolts broke!!! There was enough of a nub to get the 6 broken bolts out with heat and vice grips. The heat exchanger in the exhaust housing, as well as its gaskets were in pretty rough shape. I ordered replacements and they should be here in about a week.

The drive shaft is still stuck in the crank shaft. Does anyone know of any penetrating products that are foaming? I spray PB Blaster up the drive shaft to the crank shaft with a one foot one-fourth inch tube but the majority of the oil drips out. I cannot lift, remove and flip the motor on my own so I am trying to lube without removing the motor. Any ideas?

There also seemed to be a lot of corrosion on the water jacket side of the exhaust housing. The motor was primarily used in fresh water so it may be calcium/lime deposits but it also has been in salt water about a half dozen times since I bought the motor.

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

The driveshaft is still stuck so we removed the power head to get closer to the drive/crank connection. I am lubing it up with pb blaster and 50/50 atf/acetone. When the power head was removed there was a spring in the driveshaft housing. I have been looking at the schematics and cannot find the part.

Does anyone know what this spring is called?

 

[titleist]

Re: 1968 Evinrude 40 hp Big Twin Overheating

Hello there i am new to forum, I am currently putting together a boat for my kids (and me) a 1965 Aluminum 15 ft, Crestliner. I just bought a 1968 Big Twin Evinrude 40 in great shape. I live in Jupiter,FL. I have little experience with outboards I have owned a 25ft.Topaz with a single inboard for 18 years. Anyway r u near Palm Beach County-where did u get parts,etc. How does your motor run now. I have ordered a parts catalog.looking for service manual on e-bay. I am excited to get this classic motor running correctly. APPRECIATE ANY INPUT. THANKS

 

[kfa4303]

Re: 1968 Evinrude 40 hp Big Twin Overheating

HI titleist. Welcome to iboats. Here are some handy links. read them over and you'll be able to just about any job on these old motors. you can get most routine parts right here at iboats too. if you have any more questions, start your own new thread, so others can follow your progress from start to finish. That's a great old motor you have. well worth the efffort to keep her running. keep us posted. good luck.

http://forums.iboats.com/showthread.php?t=158086
http://www.duckworksmagazine.com/04/s/columns/max/24/index.cfm

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

Hello Titleist. My motor is still in pieces. The driveshaft is stuck in the crankshaft and will not let go. Almost thinking about repowering. I have many parts that are brand new/have not been installed and the original service manual. When she was in one piece she ran great, just had an overheating problem. Parts are readily available here on i-boats and other sites as well. I bought most of mine at the local evinrude dealer here in St. Petersburg. The motor is very easy to work on and the information here on i-boats is priceless. Research before you start taking it apart.

 

[kfa4303]

Re: 1968 Evinrude 40 hp Big Twin Overheating

hello again supagidget. you say you have the powerhead off, have you tried heating the spot where the drive shaft enters the powerhead and trying to tap it out?

 

[supagidget]

Re: 1968 Evinrude 40 hp Big Twin Overheating

Yep. Have used a small torch and a big torch with no luck. I even made a drive shaft puller than didn't budge the darn thing. It is hard to believe I have been stuck for over a month with a stuck shaft. The picture below show my drive shaft puller, which at the moment of inception I thought was genius.