Evinrude 4HP LIGHTWIN '74 - overheating?

hi everyone, this is my first post but I have been reading threads on this site for a while. Its been a great resource, so I finally signed up. Im new to boating but not to motors. I recently picked up a '74 Evinrude 4hp LIGHTWIN Model: 4406R






After I got the motor I cleaned the carb, changed the gear oil, and ran it in a bucket. It seemed to start and run just fine. I could only run it up to 1/3 throttle without throwing all the water out, so I took it out into Tampa Bay this past weekend on a 10' Achilles inflatable boat. It ran great once I got the carb mixtures set and I put an hour or so on it "zooming" around in the flats. Lots of slow speed running, some mid, and some runs at full throttle.

Everything sounds fine, and it performed great, except I think the motor might be running hot.

During the run I put my hand on the power head a few times (on the back of the motor, underneath) and had to take it off after just a few seconds. I didn't take the cover off while out on the water, and didnt touch the cylinder head itself. This motor has 8 small holes on the back of the shaft which send out a drizzle of cooling water as it runs. When the motor is good and hot the water coming out feels quite hot but not scalding. The head seems a bit discolored, maybe an indication of overheating? It was like this when I got the motor.






Today, I checked a few things:

Spark plugs - They look tan/brown, normal. They are the right plugs for the motor (Champion J6C) and gapped right at .030"

Compression - I put a gauge on each cylinder pulled the starter cord 8 times. The top cylinder read 100 psi, and the bottom was 95. These seem like low numbers.

Heat check - I ran the motor in the bucket at 1/4 throttle for 4-5 minutes, then took some temp readings with an infrared gauge while running:

Cylinder head right next to the plug: 195-200F
Cylinder mid-way down: 145-150F


I was going to remove the head and check to see if there are some blocked water passages in there. For the cost of a head gasket, this seemed to be the best next step. BUT, the 2 middle bolts are seized. I have soaked them in PB Blaster and tried a few tricks, but they wont budge and I dont want to strip them or snap a bolt, and have to drill them out of the cylinder.

So I think I will take it out on the water again, WITH the temp gauge, and check the cyinder head temps while running the motor wide open.

In the mean time, these are the questions I have:

1. Is the compression low at 95-100 psi?

2. What would the "normal" operating temperature be for the cylinder head? 200F seems high. But is that hot enough to cook the motor?

3. Is the slow drizzle of water coming from those 8 holes enough to cool the motor?



Thanks for any suggestions or ideas.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

1. Your compression is ok, might pick up a little after some use.
2. I think your engine should run somewhere around 145-160. When was the water pump impeller changed? Might want to change it.
3. It is normal for a drizzle of water to come out of the exhaust ports, without seeing the water flow it is hard to tell if you have enough flow.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

You need to change the water pump. It should be spitting water out of the relief ports if it is just dribbles the pump is getting worn. Changing the water pump is easy but you will have to open up the lower unit if you pull the drive shaft. The pinion gear floats on the shaft as soon as you pull the shaft the gear is going to drop and you wont be able to put the drive shaft back in. Fortunately it is very easy to take apart and put back together. There is no thermostat and really nothing else inside the water jacket. Since you are running it in salt water you are going to want to run it in a barrel after every use to help keep the passages clear.

Your compression is good you are looking for less than 10% between the cylinders.

The cylinders and heads on my 1975 has turned the same color as yours so I wouldn't worry about that.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

What the hell, if you haven't changed or know if the impeller hasn't been changed in the last year, change it now before you do cook this jewel!

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

382221 ? impeller assy.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

Thanks everyone for the suggestions.

The previous owner said he changed the impeller recently, along with the fuel pump. He gave me a box of parts with the motor, including the old impeller and fuel pump. But who knows, I think I will get a new one and change it anyways. Water is spitting out of the 8 holes (not just dripping down) but there doesnt seem to be a lot of it, and it feels quite hot.

I will take some new temp readings when I get the new impeller in there and see if there is any improvement.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

Just for shi*s and giggles, I would also replace water tube grommets while your at it. Just a thought! Post back yer results!

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

I took out the impeller and compared it to the "old one" that came with the motor in a parts box. The one in there now looks like its new. The water tube grommet appears to be sealing. Heck maybe the guy put the impeller on the wrong way. I will put a new one in regardless, they're cheap.

Also, at this point, I will probably just take off the power head and see whats at the other end of the water tube.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

I have the same kicker and it to runs hot to me, I put a new impeller and water pump kit, mine spits water out of the holes but I cannot put my hand on the head for more then about 6 seconds, other than that it seems to be fine I now only use it in winter as a spare.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

I will be picking up a new impeller and some gaskets today. In the mean time, I checked the water flow by blowing water and compressed air up the water tube, and it blasts out the exit hole. The volume of water flowing seems good.





So, from what I can tell, there are either some clogged/blocked passages in the cylinder head that are NOT getting enough cooling water, or the impeller isn't sending enough water/pressure up the tube. Since I can't get the cylinder head off and I'm not willing to snap a bolt and have to extract it, I am going to put the new impeller in and see if the temps come down a bit.

One thing I noticed is that the last time someone was into the lower end, they put some kind of goop or sealant on this metal plate. Do you think this is necessary??? If so, any ideas what type of stuff I should use?

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

well, I ran into another issue, there is a missing o-ring at the top of the drive shaft. This shouldnt have anything to do with the cooling issue, but it does look like it keeps water spray and exhaust from entering the motor case.



I've cleaned up the housing piece, and the new impeller is ready to go in. Hopefully I can track down one of those o-rings today and get the motor fired up.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

HI fastcat14. No worries. You can fix all of that. For starters, no, there should not be any goop on that plate. You there should be a gasket under it though. They usually come with a waterpump kit, but you may have to order it individually. You also want,need to get a lower unit seal kit. You can get them bother here at iboats for less than $30 total. The seal kit will have the missing o-ring, as well as a new driveshaft, propshaft and spaghetti seals. It's not a hard job, and there are lots of threads that can help. (I'll post one below) However, because you are missing the o-ring, you may want to check the underside of the power head for corrosion. You're probablyok, but it might be worth a peak. Keep us posted. We love the pics.


http://forums.iboats.com/showthread.php?t=277190&highlight=lower+unit+seal+kit+installation
http://www.marineengine.com/parts/s...ngine.com/parts/sierra_marine/sierra00257.htm

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

Thanks for the info. This is the website I have been using for an exploded parts view. I do not have a service manual. I will get one eventually, but for now I consider myself a good enough mechanic to do these types of jobs without a step-by-step procedure.

http://www.boats.net/parts/search/BRP/EVINRUDE/1974/4406R/GEARCASE - WEEDLESS DRIVE/parts.html

I don't see a gasket that fits underneath the plate. The previous owner gave me a box of parts, and one of them was the gear oil seal (#11 in the diagram). Even though the old seal was tight, I pulled and replaced it. I picked up the o-ring today, and installed it on the shaft.

There is a bit of rust on the output shaft that splines onto the drive shaft, but it doesnt look bad. I dont think it will be an issue. I should have the motor back together and running this evening, and I will report back on the results. Maybe with a new impeller and blowing out the crud in the water jackets, the motor will run a bit cooler. I hope so because I want to take the boat out tomorrow!

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

have a very close look at the female spline in the bottom of the crankshaft.....i had two of those motors, a long time ago, and both of them stripped that spline . same thing happened to a couple of friends of mine. make sure to put a bit of grease on the drive shaft splines when you reassemble.

Re: Evinrude 4HP LIGHTWIN '74 - overheating?

well it looks like the problem is fixed. Between putting in a new impeller, cleaning up the housing, and blowing out the water passages, the motor is running much cooler. Highest temp I got on the head was 165-175F, and the cylinder walls were around 130F. I see more spray shooting out of the exhaust relief ports too. I took the boat out on Sunday to do some fishing in Tampa Bay, and we were out there for 5 hours with a couple hours of motor run time.

The only issue was that the old plastic prop finally gave out and lost half a blade. I had to limp the boat home for a couple miles at just above idle speed. Luckily a local Evinrude dealer had that prop in stock and I just picked it up this morning.




So thanks again for the suggestions and input. Regarding the output splines on the bottom of the crankshaft, they are a bit rusty but not chewed up too bad. For what it is (a $70 motor plus the parts I put into it...) I will just run the thing for as long as it wants to keep going.