Wondering about using heat to release gearbox oil filler plug

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eddystone

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Surprisingly, I'm having great difficulty in removing the two large screws for the oil fill and level on the gearbox housing of a Mariner 2 HP 2 stroke. Shouldn't really be that difficult but clearly previous owner was determined to stop anyone ever refilling with oil (his/her approach to the spark plug was similiar, but managed that one). Admittedly probably haven't helped by painting over with Hammerite but that shouldn't make much difference. I wondered abou applying heat to the screw - I know people do this but I don't really understand why as I would have thought it would make the crew expand and fit even tighter. If the copious amount of Plus gas I've sprayed on migrates along the thread to contaminate the gear oil I haven't got much hope for the engine.
 
My sympathies. Previous person to service my engine was a gorilla!

Expansion by heat? Plenty of boiling water, in a vessel that can accurately pour. Somehow protect the screws as much as possible by shielding them with something, a tube to exactly cover the head. Now heat up the surrounding casing to get hot.

Then try to undo immediately whilst you have a temp difference.
 
I would use a fine hot flame such as from a gas soldering iron, get the plug hot quickly then use an impact driver whilst it is still hot. This will damage the paint. The rapid expansion of the plug breaks the seal at the threads.

Before this just try using the impact driver to tighten it, this might just free the thread off, so it will then undo cold.

If neither of these work, then use a larger blowtorch on the upper plug first, so you don't cook the oil inside, drain it from the upper plug hole first then invert the engine to get the oil away from the plug.
 
A trick I learnt with a seized drain plug is to hit the large flat plug quite hard with a lump hammer. This can shock apart the threads that have locked with corrosion. Combined with plus gas or soaking with diesel usually shifts any reluctant stainless part stuck in aluminium base. Don't hit it too hard as you may crack the aluminium diecasting!
 
eddystone said:
Surprisingly, I'm having great difficulty in removing the two large screws for the oil fill and level on the gearbox housing of a Mariner 2 HP 2 stroke. Shouldn't really be that difficult but clearly previous owner was determined to stop anyone ever refilling with oil (his/her approach to the spark plug was similiar, but managed that one). Admittedly probably haven't helped by painting over with Hammerite but that shouldn't make much difference. I wondered abou applying heat to the screw - I know people do this but I don't really understand why as I would have thought it would make the crew expand and fit even tighter. If the copious amount of Plus gas I've sprayed on migrates along the thread to contaminate the gear oil I haven't got much hope for the engine.
Click to expand...

The thing about applying heat is that it causes the metal forming the hole to expand at a greater rate than the metal object actually filling the hole. It seems strange but I once saw a mathematical proof that this is the case. To be effective the heating has to be applied equally to both the "hole" and the bolt or even more heat to the "hole" and less to the bolt. Just heating up the bolt is the least helpful option.

As said above, I would firstly try slowly pouring boiling water over the area for 5 minutes to get the whole area as hot as possible. Then use an impact driver if you have one or a well fitting large screwdriver through which you can apply plenty of force whilst the area is still too hot to touch.

If this doesn't work the gas torch would be the next weapon of choice but that might not be necessary.

Richard
 
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Be VERY careful about hitting screw with a hammer type impact driver or hammer- the very thin die cast casing of the gearbox may crack or be damaged.

Heat will work, along with a well fitting double handed screwdriver or an electric or air impact driver after heating.

The experts may well tell you that the hole expands and grips the screw thread tighter and say they can prove it.

All I can say is that after 45 years plus of repairing motorcycles heat invariably works in practice. The cross head screws on Japanese motorcycles could be sheared off before they unscrewed with good well fitting tools but a bit of heat and they came out real easy. Electrolosis between the Zinc plated screws, the alloy casing and an electrolite of salty winter road water froze them in real tight. Be carefull of using a powerful gas flame as the thin casing may melt. You will certainly have to repaint it!

True Knowledge is the Product of Direct Experience.................
 
RichardS said:
The thing about applying heat is that it causes the metal forming the hole to expand at a greater rate than the metal object actually filling the hole. It seems strange but I once saw a mathematical proof that this is the case.
Click to expand...

That really depends on what the hole and the item filling it are made of ;)

But I do agree that heating the plug isn't the way to go :)
 
prof pat pending said:
That really depends on what the hole and the item filling it are made of ;)
Click to expand...

True ...... but for once nature is on our side, at least in respect of expansion. If the casting and plug are both the same material, then the expansion will help free the plug. If the casting is aluminium and the plug is stainless steel (common in marine applications and probably the case here) then the differential rate of expansion actually helps to free the plug even more.

Corrosion/galling is potentially a relevant factor in both cases but I always regard corrosion as self-inflicted anyway ..... albeit self-inflicted by the previous owner/mechanic. :(

Richard
 
I would go the opposite way and use something like Freeze Your Nuts Off.
Yes, that's the name of the product, which is an aerosol designed to deliver a thermal shock.
Should be available in any motor factors.
 
Heating the screw very often works.
As mentioned above 'thermal shock' is useful, it can break the oxide layer between the two parts.
Also if the screw has been put in with threadlock, heat will release that.
The main thing is to get a tool which fits the screw very well, and that you can apply the right force to.
I find a T-handle and screwdriver bit useful.
Heat the bit smokin' hot in a blowtorch.
It's worth a try before getting the drills out.
For small, ruined philips screws, left-handed drills are often very effective. They cut a certain amount, then grab and undo!

Heat will expand the ali more than the steel screw.
It will also make the oil penetrate the thread. 3 in 1, smouldering, penetrates even better than Plus-Gas.
Putting the oil on the screw cools the screw after the heat has spread into the body of the casting. More thermal stress!
Impact driver is worth having. The sort you hit with a hammer.
If it's portable, 'take it to Dave's, he's got a windy gun' works for me. So far I have resisted buying my own....
 
eddystone said:
A result! Boiling water poured on area around plugs worked - level plug much harder but released eventually without impact driver which is good as I don't have one.
Click to expand...

Use new seals on the filler/ level plgs when you refit them

"they" say that reused seals account for the majority of water in gear oil cases
 
lw395 said:
Impact driver is worth having. The sort you hit with a hammer.
If it's portable, 'take it to Dave's, he's got a windy gun' works for me. So far I have resisted buying my own....
Click to expand...

I'm not keen on using my impact driver on alloy castings but I bought an electric impact driver from Lidl a few weeks ago which will take screwdriver bits or socket heads and it's brilliant. Only £30 and it's already shifted several bolts on the cars that would have otherwise needed the gas torch treatment.

No need for a compressor - I should have bought an electric one years ago!

Richard
 
RichardS said:
I'm not keen on using my impact driver on alloy castings but I bought an electric impact driver from Lidl a few weeks ago which will take screwdriver bits or socket heads and it's brilliant. Only £30 and it's already shifted several bolts on the cars that would have otherwise needed the gas torch treatment.

No need for a compressor - I should have bought an electric one years ago!

Richard
Click to expand...

I was tempted.
The cordless ones are nicer still.....
 
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