top end rebuild of a 1978 GS1000

[alke46]

Hmm, sounds valid. That'd mean new head and base gasket.
I'd think the 12 bolts would be enough to keep the head in place?

Just a thought here. But if the engine has not been through heat cycles, would it be necessary to replace the base and head gasket?

 

[superawesome]

Just a thought here. But if the engine has not been through heat cycles, would it be necessary to replace the base and head gasket?

Hmm, good call. I think the base gasket should still be good/dry, I am not sure about the MLS head gasket though...
But not having to take out the cylinders would be one step less...

What do the others think?

 

[superawesome]

Thanks Hannibal. As expected the rubber has swollen, and 1 day later the carbs were dry.
Will still get one from Z1, for the next carb maintenance window.

 

[superawesome]

I went to the mechanic of my dealership today, and asked for his opinion on the dowels. His said that the top dowels (between cylinders and head) were not as important, and that he'd give it a go without them. Chances that the oil flow is restricted would be very low, since the head should be kept in place. Even if it moved a tiny bit, that should be ok apparently. Another fellow (aircraft) mechanic more or less said the same when looking at it.

Bike hasn't been moved since last weekend, and as I got some time tomorrow afternoon I will go for test rides. See how the rebuilt engine behaves (and count the oil leaks ). I guess if the missing dowels have an effect, I might find out very soon.

 

[Buffalo Bill]

Well, professional experience has taught me that fk-ups need to be corrected. Taking the head off at the point you discovered your mistake would have been the easiest time to fix it.
Waiting for OEM parts is grueling, I'm waiting for a few O rings and a vent tube all this week, carburetor issues with my track bike, but that's a winter project now.
Please do a compression test for comparison to before.
Really like your thread on this top end rebuild, and may do both my bikes this winter.

 

[superawesome]

True Bill, this should be a winter project. It spoiled the whole summer for me, finding that broken valve guide. I did leave the dowels out for now, since it is time for the roadworthiness check (every two years here in CH, guess you don't have that in the US) end November, and I got to do some riding before. Will order the gaskets though, to be ready to put them in when necessary.

I took the bike home on Friday in beautiful fall weather, and the following night the temperature dropped to 3?C, we even have snow on the surrounding mountains today. It also rained cats and dogs for two days straight, seems like I am not supposed to enjoy finishing my work on the bike
I did check my shims again, and it seems the clearance increased quite a bit after some riding. I have now between 0.09mm and (approx) 0.12mm on all of them (approx means I only have 0.10mm and 0.15mm feelers on the gauge, but it is closer to 0.10 than 0.15). But I think this is still acceptable, right? I remember reading that many people here go a bit above 0.08... Opinions?

Also the bike is backfiring, but I guess the engine needs a few heat cycles for the carb boots to settle in. Or is that just wishful thinking? I replaced carb boots and (cycle)o-rings last year...

Will do a compression test, but I did not have a gauge at hand on Friday so this has to wait a bit.

Here she is, during some test riding on an old military airport.

Thanks for persevering

 

[Nessism]

The KZ1000, an almost identical engine to a GS, runs clearances up to 0.15mm so I don't think you have anything to worry about in that regard.

 

[Guest]

Thinking on your backfiring issue have your synched the carbs? you need to do this every time you do a valve shim job. And I've used the same new OEM base and head gaskets on my 1000G when I had to go back into the engine (full removal of head and cylinder) a number of times after doing a top end rebuild and putting a few 100 kms on it. Great work you're doing here by the way. How about a picture of your bike from the back showing the tank, I think you have that cool pin stripping down the tank.

 

[superawesome]

Good to hear you managed to reuse the gaskets! Since Winter is coming I might try that. Anybody else successfully done that?

I followed your advice and hooked up the carbtune today, and synced the carbs. it runs much better now.

However, it felt like I had to turn in the screws nearly fully in (vm26 carbs) to get decent vacuum. And it did not go higher than the depicted 16cmHg. Before the rebuild I had something 24ish. Does this make a difference?

btw it does have the stripey tank but I thought they all had... However I did not find a picture, will take one once I take her out again

 

[Guest]

What RPM did you have the bike at while doing the synch? Should be around 2K or higher if wanted. The stripes I was talking about are the ones on top of your tank. You’re rightl about the ones on the side being all 78 1000s.

 

[Big T]

What screws are you turning and why?

 

[superawesome]

Hi,

I had the engine idle at about 2500rpm.
Well, there is a locknut and a screw (see pic below). I loosen the locknut and at the same time turn the screw to adjust. Or am I wrong here?

Carb settings are
fuel screw: 7/8 turns out
air screw: 1 3/4 turns out


(this is an old picture, carbs are spotless clean now )

 

[superawesome]

Rob,

can you (or somebody) briefly explain why a re-shim changes the vacuum and makes it necessary to sync the carbs? Clearance changes only fractions of mm, is that enough to affect the vacuum that much?

 

[hannibal]

Don't think there's much to explain. You adjust the valve clearance in 0.05 mm increments and it's enough to affect carb balance.

 

[Big T]

Hi,

I had the engine idle at about 2500rpm.
Well, there is a locknut and a screw (see pic below). I loosen the locknut and at the same time turn the screw to adjust. Or am I wrong here?

Carb settings are
fuel screw: 7/8 turns out
air screw: 1 3/4 turns out

View attachment 56668
(this is an old picture, carbs are spotless clean now )

You are correct.

 

[Guest]

so that brings us back to the dilemma of why his vacuum is not higher than it is when synching....hmmm. When this has happened to me I remove the carbs and start over. Bench synch them, use a very thin, paper clip thickness, piece of wire to set them. You may have them set too high and compensating with your main idle?

 

[superawesome]

I vacuum-synced with carbtune on Saturday, but still somehow had unstable idle. So got the colortune out of the box (my fav toy ) and discovered that #3 was not firing in idle. Had a spark but only fired when I pulled the throttle. Ran out of time, left it for the day, pursuing other tasks (You probably know that feel when you do your shopping, stand in the produce area, and your mind wanders off, it's all about air leaks, you're muttering "check the obvious first, check the obvious first, ...").

Also a friend said, whenever it acts weird, check for air leaks, so that's what I did (again). Finally found one.
My assumption was that it should be something between carbs and engine, as only #3 was affected, so I concentrated on that area. Brake cleaner had no effect so I check further backwards. Eventually I found that one of the big clamps between air filter and airbox was not tightened. I remember loosening it when I pushed the airbox onto the carbs, but must have forgotten to tighten it again. So there was my obvious leak!

I assumed that air leaks near the air filter can't have a big effect (other than the ones between carbs and engine), but I was proven wrong and take that as a lesson.

I did not have time for a test ride yet, but the idle was really smooth at the end of my (carb- and color-)tuning. She idled stable at 1300rpm, where before I could not get a stable idle below 1500rpm. Carbtune said vacuum's about 22 cmHg, but I am not worried since it sounds smooth now. And this is roughly what I had before.

 

[superawesome]

How about a picture of your bike from the back showing the tank, I think you have that cool pin stripping down the tank.

Here it is. I am actually amazed that those golden stripe stickers stayed on there for 40 years...

Here's the tank while carb-syncing...

and on the bike