Topic: Low Compression on #4-90psi dry and cold test issue. Honda CB550

[kaptainkid1]

I have a 1974 Honda CB550 with low compression and blow by from piston #4- with 90psi.
So I have following compression test: 1-3# 120 psi dry and cold. #4-90psi.
The bike was a barn find and was sitting for 15years and the engine turned over no problem.

So I've been calling around the local bike shops regarding my low compression and possible top end rebuild and one bike mechanic who I trust told me that Honda CB500-550 have a common problem in low compression and blow by doesn't necessarily mean I need a top end rebuild. I said really? The bike starts and I rode the bike 40 miles and the bike does leak from the right side where the oil bypass and it sounds like I'm getting blow by as well from #4. My conclusion right away was top end rebuild and replace head gasket. He told me to put marvel mystery oil in the piston and could free up the carbon disposit and restore engines compression because it sat around for years. I've never heard of this problem with Honda's. I'm I missing something here? Did I not understand him correctly? If I can pass up on doing a rebuild that's the road I want to take. Another issue is the bike starts up but after couple mile ride it's hard to keep the bike idle too.
What do you guys think?
top end rebuild right!

 

[TwoTired]

No reason to be in hurry to take the motor apart.  When these engines sit there are some valves open and either through the exhaust or intake valves outside atmosphere can get in.  Humidity and oxygen make metal rust.  Cylinder walls can get rusty and even glue the piston rings to the walls.  If the rings don't seize to the walls, they then scrape off the rust which can wedge into the piston ring lands and freeze the rings into the pistons.  Yeah, that can cause blowby and compression issues.

Running the motor can free the rings and re-polish the cylinder wall.  And, everything can be well after 100-300 miles.  Or, it may not get better, the rings may not free up on the piston and the cylinder walls get scored.  Then, for sure, it needs a top end job, boring cylinders, replacing pistons, etc. which you can do up front.  Unless you have a trip planned in the near term and need a known good motor right away, drive it about locally for a while and see if it gets better or worse.  If better, money and time saved.  If it gets worse, then you will have to pay for the time and parts to make it better.  In the mean time you can be alert for someone selling their bike or good motor for a swap into your bike.   And that may well be cheaper than repairing the one you have.  Or, you might swap the used motor's good parts onto your motor's lower end, resulting in a good bike motor with years of use left.

These bikes have been known to fix themselves following neglect.  They like to run.  It just depends on how much rust built up in the cylinder during dissuse.

The other thing I might suggest is have a leak down test done to the suspected cylinder.  This pressurizes the cylinder with compressed air, and if leaking, you can hear where the air is escaping.  If past the piston, you'll hear it in the oil dipstick hole.  If the valves, then either the exhaust or carb intake will leak air outward.

Cheers,

[Flyin900]

I really like a product called Deep Creep for an engine that has sat for a number of years.

As Two Tired noted these issues can normally fix themselves if helped by the Deep Creep or the Marvel Mystery oil the mechanic suggested. I would pull all the spark plugs and spray generous amount into each cylinder let sit for 15 minutes. Place a rag around all the spark plug holes and spin the starter or kick starter if that is your only option. The oil will have leaked down the cylinder walls and some will be ejected when you turn the motor over, hence the rags or you will have quite a mess.

Repeat this a number of times (3) and the last time let it sit overnight with the oil material down in there. The next day again crank the motor over to ensure you have cleared the cylinders as much as possible of any large amount of oil. Reinstall the spark plugs and start the bike. It will smoke quite a bit initially and then quiet down and then as noted run the bike on a long ride. Usually after a few hundred miles the rings and valves will clear up and seat properly and your compression is back up to normal.

The Deep Creep is great for removing carbon from the piston heads and valves too and the oil material that leaks past the rings won't affect your wet clutch. It will mix with the oil in the sump when you are doing that few hundred miles to help to continue to clean the internals of the motor.

I would then drain the oil and change the filter after these few hundred miles and run the fresh oil of your choice and hopefully you have avoided a top end rebuild.

[BRG-BIRD]

I had a car once that had sat for a long time and sparing you the details the rings were stuck but the more I ran it the better it got, oil consumption went down the more miles I put on it. Good luck, hope it all works out for you!

[Keith]

Did you adjust the valves?

[Don R]

Deep Creep = Seafoam

[kaptainkid1]

I did do a valve adjustment to honda spec. I also let the Marven Mystery oil in all the piston for 36 hours and I ran the bike today for a couple miles and she starts up and idles better. It ran better but I know for a fact I'm still getting a leak from the valve will try deep creep next. If I can free up the carbon deposit I'm sure I can get the engine to run better and get the compression back up. The great thing is the head gasket stop leaking today on right side. I know now the gasket seal up after the engine ran for 20 miles. It sat for 38 years and I never thought about the rust build up and carbon deposit can being a problem. So I'll try to recondition the valves with deep creep.

Thanks,

Kap. 

[Flyin900]

As noted the key is to ride the bike a few hundred miles to really get the parts moving and heated up to a full operating temperature for a long period of time. The short ride you have done will help, but time and longer rides are the key.
The Deep Creep or Marvel Mystery oil is really to ensure that the parts that have sat for many years have a chance to free up and have some help from the additive materials which are designed to clean and free up stuck parts.
If that bike sat for 30 plus years then you can certainly expect that parts will be stuck and gummed up.

With use and riding and time it will hopefully sort itself out without a rebuild.

[bochnak]

I think I posted this video in another one of the OP's threads.

You need to perform a leak down test and see where the air is going:

[kaptainkid1]

So I'm going to do a leak down test and I wanted to know on this video around

: 12:50 it has the guy hitting the tappets with a piece of wood and getting a better compression and freeing up the carbon deposit on the valve seats I"m guessing. Is this true? Does the valves or piston need to be top dead center before hitting the tappets?

Right now I have Deep Creep in all the piston chambers and been riding the bike around. It seems my head gasket leak has slow down considerably. My compression results has stayed the same: 120 psi #1-3 and #4 90-100 psi.  I've noticed it hasn't changed after driving about 65 miles but the bike idles better and drives better after the Marvel Mystery Oil. So I'll try to drive another 100 miles and see if the compressions goes up.
   

[Stev-o]

Are you using an automotive type compression tester? If yes, the numbers may not be that accurate.  Typically if your numbers are within 10%, then it mat be good. #4 is a little low, continue to run the motor to see if it gets better.

[Flyin900]

Remember you said the bike sat for 15 years, so give it a chance to work its way through the issue and put hundreds of miles on it before you jump to any further conclusions. The Deep Creep will work on the carbon and stuck rings, just give it time.

If it is running and idling better be happy  .... just ride it and enjoy it for awhile now and run the tests in a few weeks after some seat time. I'm stuck snow bound here for another month, so I can only enjoy reading about you guys who get to ride year round. 

[TwoTired]

So I'm going to do a leak down test and I wanted to know on this video around

: 12:50 it has the guy hitting the tappets with a piece of wood and getting a better compression and freeing up the carbon deposit on the valve seats I"m guessing. Is this true? Does the valves or piston need to be top dead center before hitting the tappets?

I guess he is trying for a better seat seal on the valves.  But, A running engine shouldn't have bits that hold the valves open.  Also, be aware that at TDC the piston and the valves are as close as they get to each other.  Smack the tappets hard enough and you coud get contact and bend valves.  I don't really see the points for the running engine in service.  Carbon bits aren't floating about willy nilly.  Also realize that carbon build up increases compression.

Cheers,

[bochnak]

So I'm going to do a leak down test and I wanted to know on this video around

: 12:50 it has the guy hitting the tappets with a piece of wood and getting a better compression and freeing up the carbon deposit on the valve seats I"m guessing. Is this true? Does the valves or piston need to be top dead center before hitting the tappets?

I'm the "guy" in the video.

I hit the tappets to see if there was crud holding the valves open. In this case, there was, as leakage decreased.

Yes you would need to tap them at TDC when the valve is closed.

Keep in mind I used a piece of wood and light taps.

Before doing anything, perform a leak down to see where your issue is.

BTW, I've been able to tune engines with compression similar to yours and they ran pretty good. If it runs good, leave it be.

[TwoTired]

I hit the tappets to see if there was crud holding the valves open. In this case, there was, as leakage decreased.

Or...  This "could" also be a case of valve guide wear not allowing the valve to seat into normal "home" position.  Nudging the valve into "home" position with a small tap simply re-positions the valve into the seat, creating a better seal.  The assumption of "crud" is not actually proven and seems unlikely on an engine that has been running only recently.

Before doing anything, perform a leak down to see where your issue is.

BTW, I've been able to tune engines with compression similar to yours and they ran pretty good. If it runs good, leave it be.

I share this advice.  No need to obsess over "book perfection" in a street bike.

Cheers,

[bochnak]

I hit the tappets to see if there was crud holding the valves open. In this case, there was, as leakage decreased.

Or...  This "could" also be a case of valve guide wear not allowing the valve to seat into normal "home" position.  Nudging the valve into "home" position with a small tap simply re-positions the valve into the seat, creating a better seal.  The assumption of "crud" is not actually proven and seems unlikely on an engine that has been running only recently.

The engine in video has been sitting for some time. Once apart, the guides/valves seemed tight. It couldn't have been mice poop for all I know 

[kaptainkid1]

Bochnak: video

I like all the videos you put up on Youtube for Honda's CB and I've used them to reference my current problems.

After sitting overnight with Deep Creep Seafoam in all the pistons. #4 compression has gone up 120psi. So now all #1-4 is 120psi and the engine is getting better as I ride more.

My compression test tool is from Harbor Freights and if it's 10% off. It could better 132 psi or 108psi which is fine with me as long as the bike runs well. I know a good compression is 175-150psi for a fresh rebuild. So with a bike with 25750 miles on it and 120 psi compression I was told that should be ok for a bike of my age. I will deep creep the piston chamber again and see how much better

[TwoTired]

Your harbor freight Comp tester is made for cars and trucks.  It adds volume to the cylinder, lowering the compression ratio.  Not significant for a bigger displacement engine, but alters absolute for small engines.  Therefore, you cannot use Honda's numbers as a reference for the tool you've chosen, as they used a small engine compression tester to get much closer to a true reading.
There's a lot of info in the FAQ for this site.  The compression reading is one such topic in there.

http://forums.sohc4.net/index.php/topic,369.msg476032.html#msg476032

cheers,

[bochnak]

My compression test tool is from Harbor Freights and if it's 10% off.

Your harbor freight Comp tester is made for cars and trucks.  It adds volume to the cylinder, lowering the compression ratio.

I second this. The HF comp tester is junk. The schrader valve is located near the gauge, after a long piece of hose that adds cyl volume. You need a gauge where the schrader valve is located at the end of hose that screws into spark plug hole.

I recommend the Actron CP7828A. It comes with all the adapters you will need for various engines.

[Flyin900]

Just Ride On for a while!

It sounds like you motor is on the mend and these motors aren't power houses to begin with. It is more important to have the compression close in value between cylinders for a smooth running motor. Correct valve settings and correct timing and a dynamic carb sync and Bob's your uncle... or maybe a second cousin.