Logo
FULL SITE MENU

Nissan NSF6A2 Low Compression

G

Gunsmoke9150

Member
10 year old motor. ran well for years but started poor idle last year about half way thru the season. Had it serviced by a 'licensed' Nissan Dealer last winter and cannot get it to run at all. Simply wont start. It does backfire and sometimes will 'soft fire' but only 2 or 3 times and then nothing. Dealer is no longer handling Nissan and subs out his other outboard work. :(
Another Marine Repair shop checked it out and said Carb is good and ignition system is good. Low compression. They wouldnt even estimate the repair cost for me - just said the motor isnt worth it.
Given no local Nissan service shops, I am going to try and repair it myself.
any suggestions on where to start looking? Valves are the most obvious. Just dont know if this model is known for valve issues.
I have a thin, green Tohatsu/Nissan service manual ordered online. Original translation from the Japanese and very few pictures. Other recommendations with more pictures etc.?
Appreciate all the expertise here. I will need it!!
thanks
 
It should start and run even with "low" compression, albeit not well. Valve adjustment is straightforward on these, but seldom needed. If I knew for certain that the carb is good, I would get compression numbers, and probably do a leak-down test. BUT, the most common issue with these is varnishing in the low-speed sections/passages of the carb, so... It's time to start from the top, and verify fuel, ignition, and mechanical systems (IMHO, in that order). The parts catalog has a ton of exploded diagrams, which helps a lot. The current service manual for these is Part # 003-21034-1 List Price (MSRP): $26.52.
 
Thanks Paul. Understand the 'back to basics' approach but I have been told by two repair shops that the Carb is good. the first one installed a Carb Kit and said all was good. after the second one said fuel and ignition is good and the mechanical issue was going to take more time to figure out than the motor was worth, I am a bit skeptical to believe them.
Do you recommend I remove the carb and take it in to a shop to be 'cooked' or cleaned or whatever? I will check the compression myself but the last shop said it was <30 psi. I have about worn out the recoil starter trying to get it to run with no luck. It did fire up and run once for about an hour but wouldnt run at < half throttle. finally just petered out and died on me.
appreciate your help and insights.
 
Yeah, those symptoms could be almost anything, even a bad ignition system -- so, unless the shop used known-good parts and did real diagnostic techniques to verify the condition of the motor, they were guessing, you are starting at square one. So don't guess (and don't get a right-arm workout wearing out the recoil), but proceed methodically.

Given the history "ran well for years but started poor idle last year about half way thru the season", I would expect a carb issue. However, it still could be almost anything. If the compression is indeed that low, it would probably only barely run at lower speeds with a bit of choke, which is a similar symptom to a varnished low-speed circuit in the carb.

It's unusual to see a completely worn out cylinder on these (as long as the oil system is working properly, it wasn't overheated/warped, and it wasn't pounded constantly in fleet usage), so if the compression tests really low, do a leak-down test to see if the air escapes through a valve or into the crankcase. If the former, check valve lash first, especially if it's an intake valve leak. Exhaust valve leaks often burn the valve, so lash adjustment won't fix that.

If the motor was hard to start (for whatever reason), and someone was using a lot of ether-based starting fluid in an attempt to get it going, you may have a cracked ring. Running like that for any amount of time would score the cylinder. If that's the case, repairs may well exceed the value of the motor.
 
Paul: Couldnt get a compression gage to fit but I removed the valve cover and slowly brought the piston up to TDC. I could hear a "egg frying" sound quite easily with the piston up on compression. it didnt take long for it to stop until I moved the flywheel. as it came over the top it quit when the exhaust opened. I couldnt tell if it was intake or exhause side.
Checked the lash. my feeler gage didnt give me much to work with but .012 fits under both valves with a bit of effort. tight fit but not impossible to get it in. I didnt have much else to work with until I got down to .004 which fit easily.
I think the next step is to remove the power head and pull the cylinder head to inspect valves. Just need to get a few more tools.

thanks
 
You can get a cheap compression gauge on eBay, with different threaded adapters... one will fit. Tohatsu America also sells the Motion Pro gauge setups, which fits very well. They have both the compression kit and the leakdown kit. Not the cheapest, but they work pretty well. As for flat feelers, Napa and other places have long feelers with a 45 degree bend in then just for valves, and I find them the best for setting valves.

If you can get a leak-down test before pulling the head, that would help a lot. Once the head is off, you will be back to the "where does the cleaning solvent leak through ?" method. It's difficult to determine where the "frying egg" compression loss sound is weeping out, but if you do it with the compressed air leak-down setup, locating the leak will be easier.
 
Thanks Paul. trying to locate a 'leak down' kit now. waiting for daylight to get some part numbers and prices. Tried tohatsuamerica but I couldnt find the parts listing for special tools. will check tomorrow.

Mike
 
There are several leak-down testers available, but the pricing usually prevents home mechanics from getting them -- especially if they will only be used once or twice. You may be able to rent one from your local tool rental, or find one on the Internet. Tohatsu sells the Motion Pro unit, which is good, but isn't cheap. Part # 9999080126 List Price (MSRP): $166.50.
 
Paul: performed the Leak Down test tonight. at 90 PSI, it get 35% leakage. it is in the "Low" range on this cheap gage I found (harbor freight). it is clearly coming from the exhaust valve. I can rotate the flywheel a bit either way from TDC and as change the pitch a bit as soon as the exhaust valve moves. I cant even see the movement but you can see it move when you turn the flywheel a teensy bit further. There was no sound whatsoever coming out of the crankcase breather.
I measured the lash on the exhaust valve with a cold engine at .006". The .007 wouldnt slide in without a lot of force but .006 seemed just right.
I think I have a problem with the exhaust valve but what is your opinion?

thanks

Mike
 
It sounds like you have found a leaky exhaust valve. Did you ever get a compression figure? You may be able to get an adapter for your gauge from a parts house, or make an adapter from an old spark plug. If the motor was runnable, I would like to run a can of "engine tuner" through it to decarbon the combustion chamber... But since it isn't, it's time to pull the head and see what you find. Maybe just a bit of carbon junk in the valve seat... but I would expect the motor to still run, and blow that out the exhaust... If the exhaust valve is burned, that's a sign of either a severe overheat or late timing (unlikely unless there's a problem with the exciter or cd), or a flaw in the valve seat (or the valve itself). Since the cam is gear-driven, it's doubtful that it jumped time. It is possible to lap the valves in the conventional manner, just like we do with automotive valves. So... if the exhaust valve face can be reconditioned, you may have a reasonably cheap fix, since you are doing the labor yourself.
 
Tested the compression. Got 70 lbs. did it 3x just to be sure. same results each time. Book says to disconnect rocker arm on EX. I did not. would that make a difference?
Dont know where to go now. if this is correct, I guess I go back to basics and check ignition and then fuel. your recommendations? short of taking it to another shop to see if they can guess any better than i can.

thanks

Mike
 
Mike,

I would not call that reading particularly low. Not great, but certainly enough to run OK. There is a lot of variance in gauges, and the thing is that you have consistent compression. The reason the book calls for disengaging the EX rocker is that there is a weighted decompression feature on the camshaft, that makes pull starting easier. At speed, the weight does nothing, but at very slow (cranking) speeds, the decompression system makes it easier to pull.

So... your diagnostics have proven the two shops' guesses to be incorrect. You have OK compression. So it's back to square one. Verify ignition and fuel. The Factory service manual has ohm meter values for the ignition bits. Use a good analog meter, not a digital cheapie. As long as you are near the correct ranges (there is a fair bit of tolerance to coil winding resistances), and get spark at the plug, that should be OK. If so, it is time to thoroughly disassemble the carb (remove jet, etc) and give all the hard parts a 3 or 4 hour soak in real carb dip (such as Tyme). Then you can blow the dip residue out with garden-variety carb spray, and reassemble, checking float height as you go. While the carb is off and soaking, you can test the fuel pump by seeing if it delivers a spurt of fuel for every revolution of the cam. Then reassemble and test.

My bet is still on a carb issue.
 
The ignition advance on these is electronic, so it's not field adjustable. The exciter coil always fires at the same time (in degrees) -- there is no advance for a "breaker plate" like there was on older points-and-condenser models. The "brain" in the CD provides the advance according to a proprietary algorhythm that is hard coded into the circuitry. The spark advance curve cannot be adjusted, but it can be checked, using an inductive timing light; The marks are cast into the flywheel. If the ignition advance curve is incorrect, the CD must be changed out. FWIW, CD failure on these is rare.
 
Thanks Paul. I did some checking last evening according to the factory translation manual and it appears like the readings for resistance thru the Exciter coil are way off. believe it is supposed to bre 3000-4500 ohms and I am reading 15,000. I could have misread the scale but even then, at 1500 ohms it would be WAY off. Is it common to have to replace the exciter coil? would I still get spark with this reading, but not enough to 'light the fire'? I am getting spark at the plug when grounded to the block.
 
Be sure you take the resistance readings with a good analog meter, with the cd disconnected. A cheapie digital unit may not provide enough drive to the circuit under test for a good reading. Any coil can fail, and the exciter is no exception. Yes, coil resistance tolerances are wide. If you are getting strong spark at the plug, look elsewhere for now. If it's only barely a red flash at a small gap, your secondary voltage is low. That could well be due to a poor exciter. How are the resistance readings on the cd module?
 
whats the recommend procedure for removing the clear 'cover' over the connection joints on the electrical wires? Not really heat shrink but I hate to cut and peel it off. they look like they could provide some degree of water repellancy.
I will check the CD unit tomorrow. Not sure which wires to check on but Im sure the fine OEM manual I have will explain it to me in simple terms ;-)
 
Those are the waterproof covers on the "bullet" or "snap" connectors. They stay in place. Gently pull the wires apart; the covers stay on each end. If you are asking that question, you likely have not been taking proper resistance readings, so take fresh readings with a good analog meter after you disconnect the wires. The manual is written for someone with basic mechanic's skills. It's the one we use in the shop.
 
Paul: I finally borrowed a good analog multimeter. Before I make any conclusions, I want to make sure I am taking readings properly. re. pg 64 of the factory manual: Exciter coil and Pulser coil both check correct resistance. the Ignition coil is correct on the primary circuit but the secondary coil is way off. I measure 12,000 ohms resistance, not the 3-4400 recommended.
but the real question is the `table on pg 65 to check the CD unit.
I assume all readings are taken on the leads coming out of the CD unit, after they have been disconnected at the bullet connectors referenced above. I ask only because of the 30 checks, only 4 were correct, some showed no connectivity at all when resistance was supposed to be measurable and some had resistance but grossly out of tolerance.
And I cant get any spark at the plug so before I go purchasing parts that I know will cost me a lot, I want to make sure my diagnostics are being done correctly.
I sincerely appreciate your help.
Mike
 
Mike,

Yes, the readings are to be taken with the bullet connectors disconnected. Sounds like you have a cooked CD. If the exciter and pulser coils check OK, yet you don't have a decent DVA reading going to the ignition coil (typically 50-100v pulse), odds are you need a CD module.
 
well I contacted my local factory authorized service center and ask them if they could check my diagnostics before I invest in a Module. they said sure.
their first 'discovery' is that I dont have any spark. I told them that when I dropped it off and I told them the readings for the Exciter coil, Pulser coil and the Ignition Coil. they have replaced the exciter coil, pulser coil and the ignition coil and plug lead. they still cannot get it to run. allegedly, they spend 1.5 hrs on the phone with Nissan and Nissan said it cant be fixed but the service mgr cant tell me what is wrong with it. the mechanic who worked on it and spoke to techs and Nissan is AWOL or enlisted in the Foreign Legion. He was supposed to call me about 6 weeks ago. I dont want to just throw this motor away without knowing what is wrong with it. Doesnt seem too much to ask.
I am about to go pick it up and start over....
suggestions? does Nissan have any 'regional reps' that I could contact?

thanks

Mike
 
Mike,

Sounds like the shop verified what you already knew. The ignition system on these is pretty straightforward -- there are only 4 active parts, plus the wiring and the plug itself. If they changed everything but the CD and still have no spark, the CD is suspect, as you discovered long ago; As I recall, you had already verified a suspect CD by doing resistance readings.

You can call the Tohatsu/Nissan factory reps in Dallas directly at 214-420-6440. It's a relatively small company, and they are responsive and helpful. Be sure to have your exact model and serial when you call. Based on what you have already tested, they will likely recommend that you need 3R1060601M C.D. IGNITION UNIT (CU2568) NEW STYLE $114.38, available through any dealer, including me.

Please post a follow-up when you get this resolved.
 
Paul: ok I finally got in touch with the "factory trained" technician.
he CLAIMS that a NISSAN Factory Rep came out and looked at this motor. It has GOOD spark and fuel. It wont start so the answer is to tear the engine down.
I am not convinced that it is a mechanical problem. They did not check the CDI but claim it has good, strong spark.
To summarize, I performed a compression check, it is at the factory spec.
I performed a Leak Down test - 20% leakage - primarily thru the exhaust valve.
replaced Ignition coil and Pulsar coil.
Carbureator has been rebuilt 2x and soaked in cleaner 2 other times.
about the only thing that hasnt been changed is the CDI. Is it possible for that to cause the NO START and still have good spark??
:confused:
Thanks for the help.

Mike
 
Did you call the Tohatsu/Nissan factory reps in Dallas directly at 214-420-6440? It would be unusual for a factory rep from Dallas to fly to Michigan to diagnose an off-warranty 6A2. Did your local tech give you the name of this rep?

I see that there are two different symptoms/conditions being reported: No spark, and Good spark/no start. Without having the motor in my shop, I don't know which it is. I can tell you though, that if the problem has been determined to be ignition-related, and everything else is known good, the part that was not changed, even if only by process of elimination, would still be suspect. That said, again because I don't have the motor in front of me, and have not personally done the troubleshooting, there is still a wild card or two involved. Tearing the engine apart (not especially difficult or time consuming, but requires a new pan gasket) would allow checking the decompression system, and cam timing.

Since it is virtually impossible to jump timing unless a key has sheared (since the cam is gear-driven, and the flywheel is key-driven), I would re-visit the troubleshooting to get a verified diagnosis.

I thought that you had confirmed that the CD had incorrect resistance readings, was bad, and needed replaced?
 
I did not call the Nissan team in Dallas. The local tech said it was a 'regional guy'. did not give me a name.
the local tech's have replaced the Pulsar Coil and the Ignition Coil. The Exciter Coil was good. They have not replaced the CDI although when I tested it, most of the readings were way off from what the manual said they should be. Local Tech told me the motor has good spark but wont start. "It tries to start but wont fire and keep running" is what he said.
They dont know what is wrong with it, and they dont want to work on it any more. The tech who was working on it is not on any regular work schedule so I can never get in touch with him, he doesnt return my calls and the service mgr hasnt worked on the motor so he cant help figure it out. All he does is BS me.

I am going to go pick it up in a few days and start over on my own.
Question: if the CDI is bad, would it keep the motor from starting or just cause it to run poorly when it did start?
When I get the motor back in the basement, I will call the Dallas guys after I re-evaluate the symptoms and summarize what I have done.

Thanks for the patience. I will get this figured out....

Mike
 
I can understand the "not on a regular work schedule" in Michigan in the winter. I'm not in the office every day here in the "sunny south" of Buffalo, either.

The CD would usually be either good or dead... or occasionally, suffer from malfunctioning timing. A timing light would tell a lot. Once you get the motor back in your shop, start at the beginning, as something must have been overlooked. The problem that many techs have with these "simple" 1-cylinder motors is that they jump into a repair without a complete diagnosis. Happens occasionally in just about every shop. Many times I have gotten a phone call from a customer who is bringing in a motor, and almost decided on the diagnosis without even seeing or hearing the motor. Many times I'm right, but not always. If you revisit the diagnostics, and go at it methodically from the beginning, the problem will show up.
 
FINALLY got the motor out of the shop and back home. Almost 3 months of 'storage' and Im no better off than I was when I took it in. Thankfully it didnt cost me anything for storage....
Now to start all over again with troubleshooting.
does the Ignition Coil come with a plug lead and cap or is that a separate part? Catalog shows a separate number for a cap but it is not clear what you get with the Coil.
I will RECHECK all ignition components and then get some parts.
thanks

mike
 
The coil should come complete with the wire and the plug cap. The reason that the cap is available separately is because they do get damaged/worn sometimes, and a whole coil would be too costly. If the present cap looks OK, and all resistance readings are OK, the coil should be good.

If a timing light shows the spark jumping all over the place, or retarding instead of advancing, or other problem, you need a CD.
 
I hate to be so dense but how does one apply a timing light to an engine that wont start? I am still in the "get it to run" first part of troubleshooting. I will retest all electric components and evaluate the spark the old fashioned way. Shorting the plug against the block.
will get back to you on results. Thanks

Mike
 
That's a good starting point. Also ohm test the CD and coils. When you get it firing, then the old timing light shows a lot.
 
Back
Top