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engine that sat for 28 years, light rust on crank & rods ok?

Chuck78

Chuck78

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Past Site Supporter
I am building an engine for my bike out of spares, & I have an unknown mileage 79 gs750n engine that seems okay but neither the previous owner nor I have ever seen the engine run. I also have a 78 GS750C engine that was last on the road in 1985/86, and has sat ever since. The #1 pistons were at near tdc with the exhaust valves both open I believe, & the top of the bores & the rings rusted, as well as the valves rusting from moisture in the air coming in through thr exhaust. Hasn't ran since '86 as far as I can tell (I found #3 exhaust valve clearance so tight that I could spray penetrating oil in the exhaust port with the intake valve open, & see penetrating spray misting out of the spark plug hole heavily - probably left to rot due to "low compression" from lack of periodic valve adjustments.

Anyhow, the seized engine has fairly low mileage, and the unknown, "good-appearing" engine, " well, the condition is unknown unless I tear it down completely as well.

When I got the 2 pistons un-stuck, I found areas of light surface rust dusting on the top of the crank & on the rods, with a few heavier speckles here and there. Is this something that I dhould just shelve for a budget build backup engine, or can I easily clean this up & flush the crank bearings out thoroughly & run it?

This will be my high dollar build with an NOS 920cc big bore kit from MTC, and some nice cylinder head machine work done, so not sure if I should chance it (contamintaing engine with potential rust dust, and chance of rust in the crank bearings - doubt that though).

Or I should save this for my spares buildup & check out the 79 750n engine more thoroughly upon disassembly? That one I was hoping to slap some 850 cylinders and used pistons from my main bike's severely oil leaking engine, and a CV carb 850 head with some GSXR bst33ss flatslide slingshot carbs, and try it out for a budget build spare engine. Thoughts/opinions?
 
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Electrolysis works well on parts like that. I did these a while ago:

Before:

Electrolysis006.jpg


After:

Electrolysis008.jpg


It takes a bucket, some wire, rebar, a battery charger and a bit of time.
 
but with the electrolysis rust removal, you have to submerse the part in a solution of water and Arm & Hammer washing soda. seeing as how I do not want to have to press apart of the crankshaft to remove the rods and roller bearings separately, I don't know if it would be good to submerse the whole assembly with bearings and all into the washing soda solution. not sure if I can dismantle the individual gearbox parts off of the shaft easily as well, but I have not seen them yet to see if they are rusted. I will split the cases tonight or tomorrow.

Any thoughts on the washing soda solution in the bearings? just go for it & very thoroughly wash, rinse, and dry the bearings & parts afterwards?
 
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I previously just pulled the top cover, cams looked very clean, like out of a fresh engine. There was a noticeable line on 1 exhaust lobe, but I cannot feel it with my fingernail. I will post a picture of the cams later. where they clamp into the journals in the head, it looked discolored, hopefully it was not ever run out of oil, had a slight gold tint to it. Maybe this is normal? I don't recall seeing that on my other cams, spare gs850/1000 cams, KZ650, or GS650G that I've had a part.
 
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I don't know, I think I'd do it, use a spray can of carb cleaner to get the water out of the bearings as soon as it comes out of the bucket. The gear shafts in the transmission I'd do for sure, get the rust off and then spray them clean. Taking them apart and doing each piece separately would be easy enough too.
 
Cool, thanks for the encouragement. This is my first time getting into the bottom end of a motorcycle engine. I foresee at least two or three more in my near future (spare 750 build & parts pile to spare bike build, and a 550-673 top end transplant as well, so I have been reading up quite a bit & asking a lot of questions on here. Thanks!
 
If you need any 750 parts let me knw, I am parting out an early 750 engine with top end damage only, the rest is good. Also an '80 750 engine.
 
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