4500Z Spark Plug Life

[prs]

Regarding the Kubota gasoline fueled engine. I have had some trouble with spark plug service life. Our service schedule from Kubota calls for checking (cleaning and re-gapping) at 100 hours and replacement at 1,000 hours. On my 4500Z the original pugs were absolutely ruined at 100 hours. All were extremely rusty and one had rusted so badly that I was lucky to have backed it out without crushing the remains of its hex bolt area. The gap was eroded way out of spec on all, insulator cracked on one. I thought the engine had been left sitting with the plug wells flooded with wash water at the dealership or such, I NEVER used water to clean the engine. I used my blower. It is kept in a dry unheated building and I do not work when it is raining.

I replaced with new NGK BKR4E plugs set to 024? Later I noticed the second set was also poor condition at 200 hours (eroded electrode and anode, rusty, and one cracked ceramic). Replaced all verifying proper gaps. I checked the third set today at just over 250 hours, i.e. at 50 hours of service. All three were one step out of gap service limit (.032? were set at .024 new, service limit is .028?. The gaskets need replacement (can you even buy them separate?) and the hex bolt areas were a bit rusty and WET. There is no indication that the moisture is coolant or of internal source, it appears to be fresh water from the exterior, clear condensate. The plug boots look great and are tight in the plug ports, plus I coat them with silicone dielectric to help seal the plug ports.

Are any of you other Kubota gassers seeing this? I think the moisture is from the atmosphere (very humid here) due to engine cooling off after use and sucking it in, but the boots keep it from drying quickly. It also does not help that the spark plug wells are vertical and deep.

prs

 

[3930dave]

Full disclosure - I don't know your specific engine, so the following comments may be off base....

Unless those are precious metal electrodes (?), 1000 hours seems long.

Are there upgraded plugs available ? (Ex. from air-cooled world - Champion's RJ19LM has a fine-wire, longer life version. That electrode variant came out of the 2 stroke world, IIRC).

I use dielectric grease quite a bit, but recently came across something in a Ford TSB (4 cylinder road engine) that I hadn't considered. It said NOT to use dielectric grease (or anything else) on the top-of-well external seal.

I haven't had a good look at an actual top-seal, but the description said the seal was designed with small "breathing notches" that were there to relieve gases building up in the well. Perhaps to deal with a leaking plug, and prevent the whole cap being pushed up, or adding corrosion ? Their point was that the grease might interfere with venting.

Not sure exactly how you'd get moisture accumulating in those wells, but maybe they need to vent ?

Rgds, D.

 

[prs]

I have worked the 4500Z for several hours with the spark boot over-seal or top seals off. I did not realize they came off. So now, the plugs are down in "wells" in the head with normal spark wire boots on them and a good bit of clearance around them. They can "breath" all they want, LOL. No problems noted so far. I will check these re-gapped plugs after about 25 hours. I am not sure of the reasoning behind Kubota sealing the plugs in like that, but it appears as if being trapped under those top seals has overheated the plugs and then some how allowed moisture to build up as/after the engine cools.

prs

 

[3930dave]

Sounds like you were able to take the top seals off, and use the stock wires (?).

I suspect the main reason for the top seals is to keep debris out of deep wells. I'm used to them on automotive applications - they seem to do a good job there, w/o the issues you had.

In an extreme case (loose plug) you will get blow by, but I believe there is more involved in plug design (sealing at a micro level) than meets the eye. If the top seal was really tight, even tiny amounts of leakage might have been a factor....

Can't swear I've seen a modern head like that, but I seem to recall seeing heads with "drain" holes in the spark plugs wells.... probably not the case on your's though.....

Rgds, D.

 

[prs]

Yes, Dave, I simply slipped the seals off of the regular NGK plug boots leaving the assembly like it was back in the day. Debris in the wells may be an issue in the long run. The wells are big and deep, I have quite a bit of run time on them this way now and so far, so good. I use a blower to clean the motor and radiator and that cleaned a bit of chaff out of the well easily. Before plug removal, I always use high pressure air gun to blow the plugs seats clean before loosening plugs. I have about another 15 hours before I inspect the plugs again.

prs

prs

 

[3930dave]

On engines w/o your issues (at least water-cooled ones), I've found those top seals on aluminum heads are usually pretty good at keeping dirt out.

Back when, even starting out a plug change w. zero dirt in the wells, that soon changed..... cast iron heads were strong, but also good at shedding rust particles...... always good to have compressed air handy....

Sounds like your engine's plugs are happier. You seem to be piling on the hours, but it's a bit surprising that nobody else is hitting this issue.

Then again, some people defer plug maintenance until the engine won't start/runs badly....

Rgds, D.

 

[prs]

I meant to ask the dealership's mechanic what he notices and I will be there again in a week or two for a hydraulic valve upgrade, will try to ask. This is a cast iron block and head engine, a venerable design three cylinder design from Kubota. The original plugs did begin to miss fire and degrade fuel use and power. They were heat damaged badly. Runs great now.

prs

 

[3930dave]

Nice - I'm partial to cast iron in industrial applications. Can't say I've seen those top seals on iron heads, but I don't work on really new equipment often. To me, top seals are a aluminum head item...... maybe somebody signed-off on using them on these iron heads, w/o doing adequate thermal testing.....

I use copper core (conventional) plugs in certain applications - unless the plugs are really inaccessible, it's not like they are a big deal to change.

Rgds, D.

 

[prs]

IIRC, these are NGK BKR4E. They are copper core, I believe, and can be had fairly inexpensively. NGK code has hotter plugs with lower numbers, so that "4" is pretty hot. But, that is the Kubota spec and has been for a long time. I will post again when it is time to inspect.

prs

 

[3930dave]

It will be interesting to see how they do now...... the external problems may have been nothing more than a "ventilation" issue....

If you aren't dealing with fouling, maybe go with one-step colder plug next time and see if that helps the erosion issue ?

Rgds, D.