Jdub goes there 1981 650e rebuild

[DomsKat550]

When waiting for parts or other engine building delays, I'm trying to keep busy polishing parts, touching up emblems, etc.
Not sure I like the chromish appearance of the case covers. Any tips for making them look more stock in appearance? 20240810_083304.jpg

You probably figured out how to make the highly polished aluminum look more stock, but I hit the faces with horizontal 1,500 grit wet, then sides with vertical sanding.

[jdub6092]

I have decided to give the original head a try for a couple of reasons. I was able to get the cams to move freely after grinding the journals, bearings and caps down with valve grinding compound. I was quite surprised that the measurements between bearing and journal diameters were so consistent.
The head I purchased clearly had a sloped mating surface. I took it to my machinist to blast, cut valves and seats and resurface. He was apologetic about the mistakes he made decking the top surface of my original head and only charged $50 for this work. Unfortunately, it looks like he had to take too much material off the head to flatten it. It may still work, but since my original head surface is in great shape, Im more confident with it.
We'll see.

[jdub6092]

After searching far and wide on how to restore chrome, especially dull and hazy chrome, I realized that re-chroming is really the only answer if you want anything close to the original finish.
Since I wasn't going there, I instead went with the multiple rounds of sanding with WD-40. From 320 up to 5000 grit. Then buffing and polishing. Finally, I used a worn down, clean, dry piece of 3000 grit paper and went to town in a small area. I noticed shallow scratches disappearing and shine reappearing. So I repeated this on the rest of the pipes, then a final buff with lambs wool disc. Certainly no where near showroom quality, but I'm satisfied with the outcome.
20241208_110157.jpg

[Grimly]

I only have the manual for the 850, but from it you can see (using Plastigage) there's not much clearance allowed - 0.15mm or 0.0059".
I have no reason to think the 650 engine will be any different, but I could be mistaken.

image upload

[jdub6092]

Have been cleaning up the new head and taking a shot at grinding down the original. It has been a very slow process with several rounds of lapping compound to remove the absolute minimum amount of material, but I now have the cams spinning freely.
I have been tempted to just start re-shimming every valve and button things up and get this thing started and tuned up.
However, Im concerned that there is a level of precision that i first need to figure out. I have polished up the journals, bearings and caps to a fairly smooth finish (up to 3000 grit sand paper soaked in wd40), but as you might imagine, the journal widths are not perfectly uniform - lower in areas where they contact the bearings. I don't really know what kind of measurements I need to be taking to ensure proper operation. Do I need to account for expansion when the engine gets hot, how to prevent knocking, etc.

The used head that I purchased has good valves that fit nice and tight. However, the lower surface looks almost like it was decked at an angle with the mating surface a bit higher on one side.

[jdub6092]

I did go ahead and purchase a used head with cams and caps as I anticipate removing the required amount of material from cam journals and caps is going to be a crapshoot. The mechanic I spoke to said it would likely require a flapper sanding disk to remove the required amount of material.
Now I get to go back to my machinist and see if he will prep the replacement head for free after trashing the original.

FYI, while searching for the replacement head, I came across an NOS GS850 Cylinder and head for $380 OBO + tax and $60 shipping.

[jdub6092]

Back after a 3 week tour of Eastern Europe.
Was set up to purchase a new head on EBAY after making an agreement with the seller to delay the shipment.
Then my small shoulder bag with wallet, cards, cash, drivers license, passport and spare phone was stolen in Lithuania. Included the credit card I would be using.
Then someone purchased the head as I had to cancel my credit and debit cards.

I ended up stuck in Vilnius, Lithuania for four days waiting to get an emergency passport while my family continued on to Estonia and Hungary. Was Labor Day weekend, so embassy staff took off early on the Friday it happened and took the three day weekend as well with no staff available.
What a cushy job. They work 2 hours in the morning, take a 90 minute lunch, then 2 more hours in the afternoon.
Luckily, I was able to get the emergency passport on Tuesday before they left for the day. Then straight to the airport to Budapest, Hungary through Frankfurt, Germany to meet up with my family. Could have used the $2k hit to make my bike show ready.

Anyway, I'm going to first see if I can grind down the cam bearings with lapping compound. If that doesn't work, there are a couple more heads available on the bay.

[jdub6092]

There was absolutely no reason for him to machine the entire top of the head, all that was needed was to dress up the course of the sealing face, but that would have taken time and effort. The milling machine, the way he did it, was just left on its own to get on with the job, utter laziness, and moronic.
As a matter of interest, just how bad were the dings and marks? I'd bet they were easily filed smooth and filled in with steel putty.

There was one bolt hole that required welding and another couple where i attached a vice grip to see if i could remove the broken bolts. I scratched it up, but really just surface scratches and nothing too deep.. i think the extra material from the weld was the main reason he did it. Probably could have carefully filed it down and sanded to blend in.

20240826_094156.jpg What still can be with my old tank. Have an NOS tank taht will be added.
If I look at this while Im taking my break, maybe it will motivate me to get over the cam issue and get this thing done.

[Grimly]

There was absolutely no reason for him to machine the entire top of the head, all that was needed was to dress up the course of the sealing face, but that would have taken time and effort. The milling machine, the way he did it, was just left on its own to get on with the job, utter laziness, and moronic.
As a matter of interest, just how bad were the dings and marks? I'd bet they were easily filed smooth and filled in with steel putty.

[jdub6092]

Unfortunate, this guy had a reputation for quality work.
He recommended a mechanic who said he has had success at using valve lapping compound and spinning the cams by hand. However, he said he hasn't had to grind off as much as .16mm before.
Since I'm looking at a new head, I figured I'd give it a try myself. Doing it in increments. Seems to work. I can tighten the caps down a little more each time before it binds. The journals remain quite smooth.

Anyway, I got the wiring completed and everything except for the untested charging system checks out. Likely to need a turn signal relay as it is hit and miss on blinking.
Front brakes bled and grab very nice just rolling down the driveway. Suspension (front) seemed a bit soft.
Must have made a mistake on the rear master rebuild, so will try again. Internal parts are new. Think I may have forgotten to lube the rubber as it doesn't push back smoothly.


Going to take a break for a few weeks and refresh.

[Grimly]

I now think I know why I have binding on the camshafts.
The machine guy I had repair the damaged valve cover bolt threads, said he decked the top of the head also because of scratches resulting from attempts to remove the broken bolts.

Your machinist is a moron.

[rphillips]

Well, it's amazing how many folks in machine shops don't know much about motorcycles. Guessing they did get the surface flat, just a little too low, and never had clue they messed up.

[1978GS750E]

I now think I know why I have binding on the camshafts.
The machine guy I had repair the damaged valve cover bolt threads, said he decked the top of the head also because of scratches resulting from attempts to remove the broken bolts.
I cleaned up the journal bearings and cap surfaces with wd40 and 5000 grit sandpaper. I can finger tight the bolts and the camshafts still move with a small amount of resistance. As soon as I tighten them up further, the camshaft wont budge.
So close to the finish line.

20240823_200258.jpg

Any reputable machine shop would know better than to do that!

Your "machine guy" should be buying you another head IMHO!

[Rich82GS750TZ]

The way I understand it is the cam journals/caps are line bored together from the side at the factory, so each set of caps is mated to the exact position in a specific head. Well you've got practice at cleaning up and painting engine parts. What's one more head? Now to find a good used head w/ caps.

[jdub6092]

Even if I could somehow hone the journal and cap bearings to freely spin the cams, I'd be looking at a full set of thinner shims and no guarantees.
I can clearly see that the caps can rock to either side with the cams installed. I measured a 0.33mm gap when pressed down flush on one side, so I'm about 0.165 mm from the cap being flush to the surface.
If I had the bearings honed evenly, the camshafts would drop down by about 0.08mm. With my smallest shim being 2.55mm, that would become a 2.45mm shim if my math is correct.
The question is how would the journals respond to the additional 0.16mm gap?
I saw a discussion where a gs450 owner had the same issue, but thinks he lost enough material by using a brush tool designed for gasket removal. He ended up replacing the head.