Head Work Prep

[GSJim69]

I am finally getting closer to pulling the head off of my '82 850G for a valve job. I have been researching here on thin site and have most questions answered. One question I could not find the answer to is, will I need to replace the base gasket (between cylinders and crank case) also?

If I had unlimited funds I would go ahead and do a top end overhaul. However, things being the way they are I would like to keep this project limited to the head if possible. I know the more I pull apart the more I will find.

 

[hampshirehog]

If you pull the head there's a chance you'll disturb the base gasket. If the head lifts off really easily you're probably 'safe'; if you have to use a bit of tugging to get it off it's a risk.

Pulling off the cylinders isn't a big job (unless they're 'welded' on by years of road crud). Removing every last shred of base gasket is easy but a chore. Popping the cylinders back on over the rings is ok if you know what you're doing - not easy if you're a complete novice.

 

[Nessism]

This is one of those endlessly debated topics. I suggest replacing the base gasket while you are there since head gaskets are not cheap and reuseable - unless you really like to gamble. Once you pull the cylinder the new debate becomes if the rings should be replaced...

 

[GSJim69]

The rings is one of the reasons I am reluctant to remove the cylinders. I am afraid of what I might find.
If I decided to remove the cylinders how much does a set of rings cost and what is the best source for them?
The bike has nearly 40,000 miles on it now. Should that be a determining factor?

 

[Nessism]

The rings is one of the reasons I am reluctant to remove the cylinders. I am afraid of what I might find.
If I decided to remove the cylinders how much does a set of rings cost and what is the best source for them?
The bike has nearly 40,000 miles on it now. Should that be a determining factor?

How is your compression now? If it's good you can leave the rings alone.

New rings are about $100, maybe less if you search out the best price (try Part Shark). In my opinion, I'd change them at 40k miles but then I waste lots of money on my bikes.

 

[Johnny K]

When my head gasket was leaking 2 yrs ago, I got the vesrah gasket kit and replaced the base and every other gasket. Put new rings on, cleaned the head, valves and tops of the pistons with a sand blaster, lapped the valves, new seals. All because my head gasket was leaking. I'm glad I went through and replaced everything. Just a piece of mind thing to replace gaskets and everything else.

 

[GSJim69]

The last compression test results were:
#1 70
#2 120
#3 125
#4 130

I added a little oil to cylinder #1 and the compression test increased to above 90. Compression test was done with engine warm and throttle wide open.
What do you guys think?

 

[tkent02]

Have you adjusted the valve clearances?
Are you doing the head because it smokes, or because it leaks oil, or just because of the compression numbers?
Has this bike been sitting forever or has it been ridden a lot lately? And how does it run?
40,000 is nothing on these bikes.

 

[GSJim69]

I am doing the head because of the compression numbers and the fact that the #1 intake valve had no clearance and no compression. I adjusted the valves properly and rode the bike about a thousand miles and checked again. The compression numbers were still low, especially #1.
It runs OK though.

 

[Nessism]

I am doing the head because of the compression numbers and the fact that the #1 intake valve had no clearance and no compression. I adjusted the valves properly and rode the bike about a thousand miles and checked again. The compression numbers were still low, especially #1.
It runs OK though.

Sounds like the valve is burned due to crappy maintenance. Sad, but typical story.

I'd pull it down and inspect everything. Considering the poor compression I'm even more inclined to say change the rings.

 

[GSJim69]

Strange thing happened, my lady just told me to do it right the first time so I wouldn't have to worry about it again. Usually she is giving me a guilt trip for spending $$$$ n my bike.
I guess I'll tear it down and do it right.

Thanks for the advice.

 

[tkent02]

The compression numbers were still low, especially #1.
It runs OK though.

If it runs well just run it until you have the cash to do a proper top end rebuild. Not too likely you will damage anything that is not already damaged. It should be fine for years if need be.

Keep an eye on it with a compression check every once in a while, or just don't worry about it.

Also maybe keep an eye out for a parts bike with a good engine, they come up now and then.
Keep the engine, sell the rest, free engine for you. Then part out your current engine, or keep it as a spare.