Newbie here - rebuilding an 81 850

[offthepoint]

Hello all.

Name's Andrew and I recently picked up an 81 850G and I've set about rebuilding it. The idea is to teach myself to work on bikes and have a nice vintage UJM that can replace my 86 Honda Interceptor.

So far, it needs .... everything. I've removed the engine (low compression on 2 cylinders) and wiring harness (looks like something tried to eat it), overhauled the forks (leaking) and steering bearings (crunchy). Currently working on resealing the tank and overhauling the brakes.



Anybody want the old engine, wiring and controls?

Looking forward to talking with you all.

[2BRacing]

Hi Andrew, welcome here! You have certainly found the best place for loads of information on everything you need to know to get your GS running like a clock!

Why do you want to get rid of the old engine? You say you want to teach yourself to work on bikes. This is the ideal time to sort out the engine yourself. If an engine has been standing for a long time, the rings could be gummed up, leading to false compression readings. The engine also needs to be properly warmed up before doing a compression test and the throttle must be held wide open while cranking. If you have not followed the compression testing procedure correctly, the readings will not be accurate, and lead you to make incorrect conclusions. The engine is not necessarily trash. For example, the valves on those 2 cylinders could have too little (or no) clearance, resulting in low compression. Simply adjusting the valves could take care of that problem! Follow a methodical approach to check out each operating system first, so you know exactly what you are dealing with. Don't be hasty and maybe jump to wrong conclusions.

Read all the information available in Mr BassCliff's excellent collection and you will know exactly what is required to get each operating system on your bike back in tip-top shape!

Good luck and enjoy your journey of 2-wheel discovery!

[DanTheMan]

Hi Andrew, welcome here! You have certainly found the best place for loads of information on everything you need to know to get your GS running like a clock!

Why do you want to get rid of the old engine? You say you want to teach yourself to work on bikes. This is the ideal time to sort out the engine yourself. If an engine has been standing for a long time, the rings could be gummed up, leading to false compression readings. The engine also needs to be properly warmed up before doing a compression test and the throttle must be held wide open while cranking. If you have not followed the compression testing procedure correctly, the readings will not be accurate, and lead you to make incorrect conclusions. The engine is not necessarily trash. For example, the valves on those 2 cylinders could have too little (or no) clearance, resulting in low compression. Simply adjusting the valves could take care of that problem! Follow a methodical approach to check out each operating system first, so you know exactly what you are dealing with. Don't be hasty and maybe jump to wrong conclusions.

Read all the information available in Mr BassCliff's excellent collection and you will know exactly what is required to get each operating system on your bike back in tip-top shape!

Good luck and enjoy your journey of 2-wheel discovery!

I concur with 2B, your engine is most likely fine. My 850's engine does need some work, but check out the mileage on it in my sig,

[spyug]

Welcome. Are you English as you seem to have that drole Limey humour:

I recently picked up an 81 850G and I've set about rebuilding it. The idea is to teach myself to work on bikes and have a nice vintage UJM that can replace my 86 Honda Interceptor.

Anyway good for you for wanting to come back from the darkside Now we just need some pics.

Cheers,
spyug

[Steve]

Welcome, and just so you know, you did not have to pull the engine to rebuild it.

OK, yeah, it makes it easier if you are going to repaint the frame, but for stricly engine work, you can do everything you need, except for splitting the cases to get to the transmission bits, without removing the engine from the frame.

Look in my signature (click on the links, too), you will see there is a bit of 850 lovin' in my garage, too.

Feel free to ask questions before you do something that might cost you (financial or otherwise).

.

[offthepoint]

Thanks for the advice. I do intend to look into the old engine, if possible. But a replacement has already been found and is ready to be installed. The garage I'm working in is borrowed and I can't take too long.

I'll check the valves this weekend, but it seemed like the rings to me (especially on cylinder 2). I put some oil in the cylinder, re-tested and the number climbed from 65psi to 95psi, but that's still too low according to the OEM manual I got with the bike. I did read that the engine is supposed to be warm and throttle held at wide-open when compression testing, but the carbs aren't mounted. They came with the bike, but in a box.

Speaking of warm (and this may sound stupid), but I've never owned an air-cooled vehicle; how do I know if its overheating? Does it just quit? Lose power? Can it overheat?

Finally, the time will eventually come to replace the worthless tires. Anybody have any favorites to recommend?

[offthepoint]

Welcome. Are you English as you seem to have that drole Limey humour:

Not English, no. But I do watch a lot of Top Gear. I'm a delightfully unusual mix of Hawaiian and Scottish. Like a plaid pineapple.

[Nessism]

How many miles on the first engine? I may be able to take it off your hands if it's not too far gone.

[offthepoint]

How many miles on the first engine? I may be able to take it off your hands if it's not too far gone.

Well, the odometer reads 35k. Now, this bike was found in Lancaster as abandoned property and was last registered in 1997. So is that accurate? No idea. If you want it, I'm sure we can work something out.

[Steve]

I did read that the engine is supposed to be warm and throttle held at wide-open when compression testing, but the carbs aren't mounted. They came with the bike, but in a box.

Don't fret about the carbs not being mounted, just so you can hold them wide-open to do the test. Actually, having them off is the best, but very few mechanics want to go through the hassle of removing the carbs off an hot engine, so we just hold the throttle open to make sure the engine can breathe as much as possible.

And, with the carbs already off the bike, that is the PERFECT time to rebuild them. Do NOT waste your money on rebuild kits, though. 99% of the time, all they need is a good "strip and dip" cleaning, followed by a new set of o-rings and possibly new float bowl gaskets.

The "strip and dip" procedure is shown HERE. You will need a can of Berryman's or GUNK brand carb cleaner dip (about $20), a set of o-rings from cycleorings.com and I would recommend also getting the intake boot o-rings and the stainless bolts that hold the boots to the head, also from cycleorings.

Speaking of warm (and this may sound stupid), but I've never owned an air-cooled vehicle; how do I know if its overheating? Does it just quit? Lose power? Can it overheat?

Yes, it can overheat. Depending on how badly it is overheating, you will notice a loss of power, which will likely be due to the pistons expanding to the size of the cylinders, instead of their usual clearance. As long as you have your carbs jetted for your intake and exhaust plumbing (stock is pretty close to "best"), there is little chance of overheating. Just try not to have the engine idling for extended periods of time, especially after running warm, like a freeway run that suddenly comes to a traffic stop.

Finally, the time will eventually come to replace the worthless tires. Anybody have any favorites to recommend?

If the tires are already "worthless", that eventuality has already happened.
If you see any cracking in the tread or if the tires are more than about 5 years old, they need to be replaced before leaving your driveway.
Read the date code on the sidewall, you may be amazed at how old they are.

Favorites? That depends on your budget and your riding style. For casual riding, but with a surprising amount of grip, many of us are using Shinko Tour Master 230. About $130 per set, shipped to your door. You will have to install or arrange installation.

For a bit more grip, I think the preference is toward Avon Road Riders or Pirelli Sport Demons. A bit more money, a bit less life, better performance while they last.

.

[offthepoint]

Thanks much Steve. A carb rebuild is in order and now I have a perfect guide for the process. Looks like this weekend is going to be spent at the workbench (as it should be). And you read my mind for the hardware that holds the boots to the head. Removing the old, stripped #3 Philips screws was a real party. But its done and fresh set of stainless hex screws (pilfered from work) are ready to go in.

So air-cooled engines can overheat. Looks like Pops owes me some money...

I can't help but smile at your tire recommendations. Pops' CX500 has Shinko 230s, my Interceptor has Avon RoadRiders and his Interceptor has SportDemons.

[Steve]

So air-cooled engines can overheat. Looks like Pops owes me some money...

Yeah, they can overheat, but they are not prone to coolant leaks.

.

[offthepoint]

Yeah, they can overheat, but they are not prone to coolant leaks.

.

So what do you fill the radiator with?

[Steve]

You have to understand that the "radiator" is the whole engine.

Therefore, you fill select portions of the "radiator" with a correct mixture of gasoline and air, then ignite it.

.

[Nessism]

Well, the odometer reads 35k. Now, this bike was found in Lancaster as abandoned property and was last registered in 1997. So is that accurate? No idea. If you want it, I'm sure we can work something out.

Sounds cool.

Low compression on #2 sometimes occurs when the petcock leaks back down the vacuum line and into the #2 carb, thus washing down the cylinder with too much fuel and gumming up the rings. Sounds like you should inspect/test that petcock carefully.

Drop me a PM when you figure out for sure about the engine. Simi Valley is a bit of a drive for me, but I'll deal with it for a free engine.