Topic: 1978 CB750K blue smoke

[JimsCB750]

My 1978 CB750K with just under 22,000 miles is blowing blue smoke at all RPM's.   I changed the oil and filter yesterday, used Rotella T4 15W-40 and added 3.5 ozs of Seafoam to the engine oil to see if that will help with some run time.   From what I am told, it sat for 16 years in dry storage.   I am getting 100# compression with throttle wide open across all 4 cylinders which makes me think the rings are stuck on all 4 pistons after soaking the cylinders with Seafoam spray for 4 days and moving the crankshaft and adding a little more spray each day.   I got about a 5 to 10# gain from when I started the process since it was in the low to mid 90's across all 4 cylinders.   The compression comes up quickly with added oil in the cylinders so I'm focused on the rings being the culprit.   

Is it time to give up on the Seafoam spray and deal with new rings and possibly a cylinder bore job?  I plan on giving the Seafoam treatment in the engine oil time to work its way through the system to see if they will free up with some run time.    Are there any other suggestions on soaking the cylinders with something other than Seafoam spray since it looks like a made a slight gain in compression?   I've avoided using Marvel Mystery Oil in the cylinders since they say not to use it in a wet clutch.   Thank you for your input!!!

[kerryb]

following, I have a similar situation on a '78 550k with 23k miles.  great power, but sending smoke signals when shifting (clouds of blue smoke)

[bryanj]

The 750 will be bad guides and seals, the 550 stem seals or siezed

[madmtnmotors]

My money is on valve seals. Ride it a while and see if it clears up or if you can just live with it. Either way (valve seals or rings) require removing the engine from the frame unless you hack up the frame...

[Flyin900]

If you want a better product to soak the rings in use Deep Creep from the same company as Seafoam. Any bike that has sat for years I always soak with Deep Creep to assist the stuck rings. The Seafoam in the oil is a good idea and riding the bike for an extended ride, not short riding will help release the rings if they are gummed up.

[ekpent]

 Have you taken it for some long rides incase its oil or other material in the exhaust pipe/pipes that needs to be burned out. Most anything going in the spark plug holes will end up in the pipe for awhile.

[PeWe]

+3 for a long ride

[JimsCB750]

The constant blue smoke has cleared up since I've been driving it.

[BenelliSEI]

Visit Randaak’s website on early Honda GL1000 Goldwings. Root around until you find an article about restarting dormant, “barnfind” bikes. He uses a routine with automatic transmission fluid replacing engine oil for a good “flush”. I’ve done this on a couple of engines, followed by a few quick oil and filter changes, with amazing results. Check it out, follow his directions and you may be surprised at the results. I was.

[ekpent]

 Good news on the smoke. As for the compression numbers some gauges are far better then others. If the numbers are basically all the same thats a good thing. Harbor Freight for instance gets bad reviews for theirs on their own website for being inaccurate.

[PeWe]

There is no standard for compression gauges, right?
The lenght and inner thickness of hose adds to chamber volume.
Good when comparing cylinders to be equal and other builds with same gauge. See the compression change after modification.

My stock K2 had around 150PSI with this gauge. Rather fresh bores and pistons.
Hose must be long enough to reach the inner cylinders.

[rotortiller]

The length and inner thickness of hose adds to chamber volume.

If its got a Schrader like check valve in the end near the cylinder head it will work fine. The valve allows combustion pressure to build up just like a bicycle pump LOL

[PeWe]

The adapter that is threaded into the plug hole has a valve. So the pressure will pump up at each stroke and finally same pressure in hose as in chamber and gauge that also has a valve? Button for let it out.

I read this post earlier.
http://forums.sohc4.net/index.php/topic,369.msg476032.html#msg476032

It might not take the "pumping up the pressure" function with one way valve in consideration?

I should be sure if I could measure on a known pressure in the 150-210 PSI range.

[JimsCB750]

UPDATE:   I have the cheap Harbor Freight compression gauge.   I appreciate the input and feedback on getting an accurate compression reading.  I have put about 250 miles on the bike since purchase in mid-October.   The blue smoke has disappeared.  I used Seafoam spray initially in the cylinders and then changed the oil and filter.   Right now, I am running 1 oz per quart of Seafoam in the engine oil (Rotella T4 15W-40) to keep cleaning the engine.  Oil level is staying the same since changing the oil.   

I now have the engine running good by installing a Dynatek electronic ignition, cleaning the carbs,  installing new carb intake boots, removing the pods and installing the OEM original air filter box that came with the bike.   I would like to replace the 4 into 1 exhaust with 4 into 2 or 4 into 4 like the original.   The only 4 into 2 chrome that I can find is MAC Megaphone.   I'm very happy with my first CB750K.   My primary bike is a 2001 Honda Magna.   

[ekpent]

 Nice that you came back for an update. Lot of dead end threads on here sometimes with no answers or results at the end. Can be frustrating when doing a search.

[HondaMan]

I think I would recommend switching to the proper weight oil, now that the rings are freed up again. That's 20w50 in this engine: the present-best 'normal' oil I have found is the Bel-Ray EXL Mineral series, made expressly for bikes like these. The even-better-but-more-$$ type is the Golden Spectro in 20w50 (not the V-Twin stuff, that will make your clutch slip).