Topic: Engine seized,pb blast and its good?

[pat english]

Its been a while since ive been on.I had to sell my last cb 750 project and i got side tracked with a car for the past 7 months..Anyway,sold the car an here is the new project.1978 cb 750.When i brought it home its was seized up.I got a can of pb blaster and squirted a bunch in the spark plug holes.I let it sit for about 10 min then put it in gear and rocked it back and forth a bit and it freed right up.I was pretty amazed how quick this worked.All the spark plugs looked good but one.See the pic below.From what youve read,does this sound like an engine that was seized from lack of oil,or does is sound and look like it was just sitting for a long time and got jammed up with dirt and water?I ask because im wondering if i can just get away with cleaning #$%* out and trying to fire it up.let me know what you think.thanks,
                                                                                                                  pat

[dave500]

more of that crud on the plug will be inside and as soon as you start to spin it over it will grind away at everything,id pull it down,plenty of people have had luck just forcing them to start after being seized or slightly seized.

[phil71]

fill that thing up with PB blaster.. turn it a little every day..
DON"T FIRE IT for awhile. THat plug is on the one cylinder that had a valve in the open part of the cam cycle. IT was probably the frozen one.
Thing is, those rings are probably seriously glued into the ringlands, so I wouldn't expect much compression there right away.
after it gets nice and easy to spin. i'd put cheap, fresh oil, substituting half a quart with diesel fuel. Spin it on the electric start a bunch and get oil up.
  at this point, you can try to fire it (after cleaning the hell out of the carbs, obviously). Run that for 10 minutes and drain the oil. Put better oil in it, and hope for the best. I think it'll be okay, based on what you have found so far.

[pat english]

thanks for the responses guys...so where could that rust have came from?could the rings have rusted and fell apart?what was that crap that flew out when i kicked it over?
 why diesel?i herd guys dumping atf in car engines in this condition and letting it run for while and draining it.would that be a bad idea for these bikes?
can i do any more damage by trying to run it after i get all that crap out?

[ekpent]

That rusty plug is a little disturbing as it does indicate what condition the rest of that cylinder is probably in.Was that puppy stored inside or out in the elements?.

[Stev-o]

The rings in that cylinder probably risked to the cylinder wall, and it stuck. Doubt the rings fell apart.
Personally, I would try to fire it, to see what you have. Regardless, a top end rebuild appears to be in your future. Go 836!

[killersoundz]

I too purchased a 750 with a seized motor.

It turned out only 1 cylinder had rust in it. I suspect the exhaust valave was open on that cylinder while it sat.

The rings were rusted solid into the piston and there was some rust buildup on the cylinder wall.

If I had turned the motor over like that it would have damaged the cylinder wall and would have had to be bored out. The piston rings also wouldn't have just come unstuck by themselves so the compression would have been crap and also cause damage.

If you got the motor free and it turned with just the kicker it must not have been that bad. However after getting into my motor I would never try to just free up a seized motor and run it. Top end rebuild is in order in my opinion.

[KJ790]

Personally I wouldn't bother trying to start a motor that was seized for any reason. I would tear it down and fix the actual problem. I'm sure lots of people on here will tell you to just try to start it up, but you are more likely to cause more damage and cost yourself more money by doing this.

[phil71]

if you get close numbers on a compresssion check, i say go for it. If that rusty one comes up really short, pull it apart.

[Jerry Rxman Griffin aka MuthaF'er]

If you don't back off the rocker arms when you "store" your bike there will always be a cylinder open to the external environment allowing moisture inside. Moisture = Rust.

[bollingball]

78 had one front fender stay yours has none piggy back shocks barnet racing clutch I was going to say try to fire it up but that plug looks pretty bad. I think you will need a 836 kit so why not soak it good and try it. Do what phil71 said

Ken

[pat english]

right on thanks for all the responses..it says 78 on the title..anyways,i think i will just do the top end rebuild anyways.anyone know any shops in LA/oc area that have experience  with machine work on these bikes?what should i expect to pay for a bore and hone?

[killersoundz]

right on thanks for all the responses..it says 78 on the title..anyways,i think i will just do the top end rebuild anyways.anyone know any shops in LA/oc area that have experience  with machine work on these bikes?what should i expect to pay for a bore and hone?

You may not have to bore it, unless you want 100% assurance that it's done right. My cylinders were all well within spec with the bike at 30,000 miles, and I honed out the rusty one and it's looking like it will be fine. I'm just replacing the rings, gaskets, I lapped the valves (they needed it) and cleaned everything up.

[killersoundz]

If you don't back off the rocker arms when you "store" your bike there will always be a cylinder open to the external environment allowing moisture inside. Moisture = Rust.

Yup that's what happened to my engine. Cylinders 2 and 4 were pristine, 1 was the real trouble maker, and 3 was ok but could tell a valve was open too. There were also spider webs inside my engine! Mostly up under the 6 rubber pucks under the head, real bad

[chewbacca5000]

Personally I wouldn't bother trying to start a motor that was seized for any reason. I would tear it down and fix the actual problem. I'm sure lots of people on here will tell you to just try to start it up, but you are more likely to cause more damage and cost yourself more money by doing this.

+1 on KJ he know his stuff!!  If the bike has over 10,000 miles the cylinder metal according to Hondaman has completely cured and by doing a 2nd over piston .5 you can reclaim 5 to 7 HP.  Z1 has the kit I used and I could not be happier.