LOWER END OIL CHANGE

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zuchero

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I have a 1976 850 HP Thunderbolt which I just drained the lower end oil on. I looked up the torque spec for the drain and fill plugs and can't find it in my service manual C-90-74041. Does anyone out there have the torque spec and where would I find it?
 
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Jeff J

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It might be a generic torque table item for the thread diameter and pitch if the plug isn’t specifically called out.
 
alldodge

alldodge

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Don't have one that old. Checked Mercruiser Alpha and Bravo and they are 40 in-lb. The Verado OB is 100 in-lb

This manual list 55 in-lb
MODELS 135-150-175-200-225 1992 and Newer – 135-150-150- XR6-150 Magnum III-150 EFI-175-175 EFI-200-200 EFI-150-200-225 Pro Max-150-200-225 Super Magnum

I just set my elbow and a big screwdriver and twist it tight
 
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Chris1956

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You will want to install new fiber washers on the two plugs. Make 'em tightest as possible with a screwdriver. A couple of taps with a hand impact driver to tighten them, is a good idea as well.
 
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cyclops222

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How do you know what to set the impact driver to ? What peak Foot Pounds can be checked ?
I changed mine to S S Allen Head Screws. Easier to build up enough pressure slowly.
 
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Chris1956

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It is a hand impact driver. You hit it with a hammer to tighten or loosen screws.

Don't hit it too hard, for low tightening, harder for more tightening. The plugs will stop getting tighter on their own.
 
Texasmark

Texasmark

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I always used a screwdriver sized to adequately fit the slot in the plug. Installed the new fiber washer and with two hands on the screwdriver, got it good and tight. Same for the vent screws you remove to help in draining, and ensuring the LU is full of oil. Never had a problem.
 
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Jeff J

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I was just thinking about this. I have yet to see a screwdriver or bit that properly fits a lower unit pan head style drain plug. The manufacturers give us torque data but not many can turn a screwdriver that hard and the angles the work is being done is not very stable for using a narrow bit on a torque wrench. I just used a torque wrench to install the plugs on a Volvo Penta SX-A but that is a 9/16” socket. I use to attempt it on the slotted plugs but was damaging the slots 50% of the time so I gave it up.
 
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Chris1956

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Jeff, hence the use of the hand impact driver. You first make the screws as tight as possible with a screwdriver, then use the hand impact driver and a few taps from the hammer to tighten them a bit more.

I first used it on the Phillips head case screws of my old motorcycle. It was essential to remove the cases and covers.
 
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Jeff J

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I use the hand impact to loosen stuff all the time. I may have to try it for tightening but beating steel threads into something with aluminum threads makes me nervous.
 
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airshot

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cyclops222 said:
How do you know what to set the impact driver to ? What peak Foot Pounds can be checked ?
I changed mine to S S Allen Head Screws. Easier to build up enough pressure slowly.
Click to expand...
Get a " low head" bolt....looks just like a factory plug but has a hex drive in the center. Often the outside dia of the head is to big to fit the recess so chuck up the bolt and grind the head dia down until it fits. Much easier than messing with a slotted head screw !
 
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Jeff J

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I just did that with a slotted pan head screw on a Volvo Penta. Threads were stripped and the helicoil took out the sealing surface for the o-ring. Switched to a wide head screw and a gasket. The screw head had to ground down to fit inside the lip around the hole. Easy, straight access so torque wrench was used to install.
 
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Chris1956

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To each his own. I for one, do not want the gearcase plugs leaking or unscrewing, while I am cruising along.
 
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