Base Gasket changeout?

[Guest]

I'm replacing the head gasket on an '80 GS850GL. Do I need to change the base gasket as well? The bikes has 16,200 mi only 1,000 are mine.

I've done the shims. Working on the carbs while waiting for the gasket kit. Is there anything else I should do while I'm this far into it?

Any guidance would be appreciated!

[gs1197]

If it's not leaking now, and you don't unseat the cylinder when you remove the head....should be no need to change it.

[Suzuki_Don]

Definitely replace the base gasket. As soon as pressure is released when head nuts are loosened there will be a release of pressure on the base gasket. If you do not replace it while you have the head off, then it will leak at the base of the cylinders afterwards.

Also one must ask why are you replacing the head gasket after only 16,000 miles. If I were pulling the motor down that far I would pull the cylinders off and check the rings are all OK (not broken) and are free in their grooves on the pistons. That ring lands are OK.

[Riding Again]

This is why I'm changing the head gasket.


After Cleaning and running



I was siting in a smoke screen when I came to intersections with the leak.

Before confirming the leak, I washed the engine clean and then started it up and ran it at 3000 rpm for about 3 minutes for this much to show. When I confirmed the leak, I shut it down.

[SqDancerLynn1]

I would change it just to be on the safe side. It is not that much more work, when you already have the head off.

[psyguy]

Definitely replace the base gasket. As soon as pressure is released when head nuts are loosened there will be a release of pressure on the base gasket. If you do not replace it while you have the head off, then it will leak at the base of the cylinders afterwards.

Also one must ask why are you replacing the head gasket after only 16,000 miles. If I were pulling the motor down that far I would pull the cylinders off and check the rings are all OK (not broken) and are free in their grooves on the pistons. That ring lands are OK.

i second all this

also confirm that theres no nasty play in the connecting rods
measure the cam chain for stretch
inspect the head/cylinders for bowing and plane if necessary
dont forget the cylinders orings (the underside of the cylinders)

even though the bike is "new" milage wise, it's not so new age-wise, so it pays to check now everything is in spec

[gs1197]

In the "for what it's worth dept".
I've had the head off the dragbike 3 times in the last few years, and have yet to change the base gasket.
Has never leaked a drop of oil.

If there was no evidence the bottom end needed attention, I would slap a new head gasket on and haul A$$.
Releasing the torque on the head bolts shouldn't cause the cylinder to break the base gasket loose UNLESS the cylinder is moved.

16K isn't a lot miles, and if the bikes been maintained reasonably well I wouldn't think it's due for a rebuild.
But if you have nothing better to do and it makes you feel better...then tear into it.

Mike

[hampshirehog]

I tend to agree with gs1197 (but all bikes are different). If your cylinders have got crudded up, as most will have done in the UK for example (unless religiously kept clean), the chances are that your cylinders will have become 'welded' to the studs / crankcase through corrosion. If this is the case your cylinders will stay put as the head doesn't usually get stuck down.

If you cylinders are stuck down, and you decide to lift them off, be prepared for a struggle and clean the outside fanatically to try and prevent any crud falling in to the crankcase void.

[Fast Doc]

What I've done when I changed the head gasket of an '80 GS1100 was have the head done (new seals, milling the face, valve job etc.) and pulled the block. Changed the O rings. It is very little additional work and cheap insurance. Imagine the feeling when your head gasket does not leak and your base gasket does and you get to do the whole job over again.

I also had new rings fitted and the cylinders honed.

Sort of a top and 'middle' rebuild.

The GS had about 50,000 miles whwen I did the work, and I sold it at 75,000 to a friend. Last I heard (years ago) it went over 100,000 with no further work, or leaks.

[Nessism]

I'm in the replace the base gasket camp, particularly if the gaskets are the origionals - they get hard and brittle. If you have a drag bike and/or have replaced the top end gaskets within the last few years, it might be worth taking a chance.