This Nissan 5B don't run

[BadBear603]

OK I bought an older mid 80's two-stroke Nissan 5hp. Ran good for 2 years then I had some shutdowns. Cleaned and rebuilt carb. Ran OK for awhile but started bogging down and cowling was very warm to touch. Cleaned carb again and it ran but bogged at higher rpms, again cowling seemed warm. Has totally quit on me and can't get it started. Carb bowl is full, plug gets good spark-reddish brown color-wet after trying to start. 6 ohms between plug wire and block so I think fuel/spark OK although fuel pump diaphragms old & saggy (aren't we all!). 60 psi compression after four good pulls (low I think). Good water flow even while just trying to start. Last few times I have tried to start I have gotten a loud pop and some electrical/gunpowder smell. I did take the flywheel off at some point and heard you can get some probs if not properly retorqued. Also changed out lower unit fluid when I first got it - stank bad and was black. HELP! thanks.

 

[pvanv]

Re: This Nissan 5B don't run

That compression is way low. Might run like that, but not well. If it got very hot, you may have salt/crud in the powerhead, which could cause an overheat even if the telltale is flowing. That could cause a warped head or bad head gasket.

The spark should be hot blue. The flywheel needs to go on dry and be properly torqued, or it could come loose. If you are getting a pop through the carb, you may be lean, out of time, or very very low compression.

 

[jrs_diesel]

Re: This Nissan 5B don't run

Is there a compression release on these engines (4/5/6) to help with starting? If so, that could explain the low compression reading.

 

[pvanv]

Re: This Nissan 5B don't run

nope. not on a 2-stroke.

 

[BadBear603]

Re: This Nissan 5B don't run

Thanks for your response Paul. The spark starts out blue then gets brighter and yellow at end of pull. There is a lot of crud around the head gasket so I might have to check that route. I'm hoping the pop was from being lean - I had adjusted that by seating screw then backing out 1 1/2 turns. Should I just back it out some more, try to get it started, and adjust from there?

 

[pvanv]

Re: This Nissan 5B don't run

Sounds like you have a decent spark. So if it's firing in time (you can see where the timing mark lights up by using a timing light -- even if it doesn't start)... that leaves fuel and mechanical areas to check. Can't hurt to open up the pilot screw some more, but that should not prevent it from cold starting with the choke on -- as that's a ton more gas than the pilot circuit flows without choke. If you have the chance, try doing a leak-down test. If you don't have a leak-down tester (typically used on 4-strokes), use the compression gauge to see how fast the pressure drops off, and see if you can diagnose where it's weeping out.

Since you noticed that the cowl was very hot, and it was having issues at high RPM, you may have clogged cooling passages and overheating. Much of that can be cleaned out if you pull the head and pull the powerhead off of the exhaust housing, then of course install a new base gasket and head gasket after you have verified that the passages are clear. Is any of the paint discolored (a sure sign of severe overheat)?

 

[BadBear603]

Re: This Nissan 5B don't run

Paul,
There is no discoloration but I plan on pulling the head to clean out the cooling passages. The compression is low but holds steady so not sure what's going on there. I will check the timing as you suggested. Thanks

 

[jrs_diesel]

Re: This Nissan 5B don't run

nope. not on a 2-stroke.

Good to know, thanks Paul.

Herald, did you check compression when the engine was warm or cold? Readings will be different between the two.

 

[TOHATSU GURU]

Re: This Nissan 5B don't run

Runs the test on the ignition system as found in the factory sevice manual...Pay special attention to the trigger coil.

 

[BadBear603]

Re: This Nissan 5B don't run

OK guys. I removed the cylinder head and lo and behold it was a bronze color - other parts gray. There is a crack from middle of top bolt hole halfway down to next bolt hole on right. Need new cylinder head but any suggestions on what else I should do while it's opened up. Old cylinder head all clogged up just want to make sure I don't need to go deeper. Thanks.

 

[pvanv]

Re: This Nissan 5B don't run

The parts you need are 369B010011 CYLINDER HEAD $42.47 and 369010052M GASKET, CYLINDER HEAD $13.52. Make sure all cooling passages are clear. I would verify ignition before spending too much on this vintage motor. As Elvin said, verify ohm specs on the trigger (pulser) coil. These 5 hp 2-strokes run a long time and take a ton of abuse, but nothing is forever.

 

[BadBear603]

Re: This Nissan 5B don't run

Paul,
I have installed the new cylinder head and compression is back up to 110 (no big surprise). Started right up and I let it idle. Water flow was good through telltale. I kept my finger on the cylinder head and it was a little warm for say 15-20 seconds then started really warming up - I could still touch it but not for more than a second. Is this normal at idle. Just wonder what will happen under load - I don't want to crack another cylinder head crossing a shipping lane in our 4 knot current.

 

[pvanv]

Re: This Nissan 5B don't run

Head temperature testing by touch is a subjective thing. Usually these motors will get hot enough that you can't hold your hand on them, but cool enough that touching them does not burn you. Good flow from the telltale is one part of the cooling system... it shows that your cooling system is pressurized to the powerhead base. But you could still have clogged passages. While you had the head off, did you inspect/clean the block passages? Did you make sure that the lower passages were clear as well? You would need to pop the powerhead off at the base to see those. If they looked clear, and the telltale is flowing, you should be fine.