Topic: Top-end job cb550 - diagnosis and tips, please...

[Franky]

Hi guys

My 1978CB550 has been running quite good all last season. I bought it in spring, from a guys that had a mechanic do some work on the engine. I think he built one engie from two. I was told to go easy on the rev's, since rings were new and such. I did for at least 1000 kilometers. However, at the end of the summer it started to develop an oil leak from the top (see image with red marking) and to smoke from the exhaust (blueish smoke). I've taking the top off to fix these issues...

Question:

1. Is my leak bad? I've read that lots of guys just live with the leaking and use tissue stuck in the fins. I'd be OK with that, but I don't know what would be considered too much. (I would then know what to live with if it comes back after I put it back together).

2. The smoking: Before taking it apart, I did a compression test: 162,5 165,5 160,5 162 - so pretty good I think. I plan on lapping the valves and install new valve seals. Any other advice or tips to get rid of the smoke.

3. What's up with the white valve? Lean mix I guess, but what could the causes be? No juice from carb? I discovered that the spark plugs were different (PO): 2 x NGK D8EA and 2x NGK R DR8ES! I have pods but otherwise all standard, don't think the PO rejetted the carbs. Which new ones should i get? These: http://www.davidsilverspares.co.uk/CB550K3/part_29019/   (NGK DR7ES)

4. How the top end looking? Check out the tappet wear. The close up has the one tapet that look somewhat worse than the others.

5. As I pulled off the top, the cylinder got loose from the engine. Not as in apart, but the wiggeling to get the top off, made it separate a bit. Will it stay tight? Or should i pull the cylinder and replace the gasket?

6. Finally: Is there anything else you'd recommend me to do now I have the top off. I'd like to invest $$$ and time to make it a great, strong running bike.

Let me know if you'd like more, better, closer images.

Thanks, Frank

[dave500]

they fitted two wrong resistor plugs with "r"in the number,just buy four new ones without r in the number,seating the valves and seals is a good move,check how sloppy the valve within the guide may be,you might need to carefully file off any small burr on the valve tip so it can be removed through the guide,dont just force it.,,id pull the barrel of and check the ring gaps aswell now its apart.you can gently draw file with a very fine file the head and barrel around the ends at those o rings to make sure its flat to prevent that leak you have.the po might have even just reused the old o rings?i cant make out the tappet wear,is the hard face peeling?is it rattly sounding?how do the cam lobes look?and where the cam rides in the head and cover?do the rocker shafts have any slop wear they ride in the cover,screw a 6 mm bolt into them and wiggle them around to check.

[sscardefield]

2. The smoking: Before taking it apart, I did a compression test: 162,5 165,5 160,5 162 - so pretty good I think. I plan on lapping the valves and install new valve seals. Any other advice or tips to get rid of the smoke.

I am contemplating a top end rebuild right now as well. Before ripping it apart I am trying to make sense of my compression numbers. Yours are pretty damn good, considering the Honda shop manual says 170psi. I was just wondering if you could post a picture of your compression tester. I am curious to see how big the hose is on it. And is it specifically for motorcycles (smaller engines in general), or did you just get it at the local auto parts store and it was probably meant for cars (larger engines)?

Thanks.

[dave500]

mines this long.

your tester must have a valve at the thread end,,a longer hose only takes a few more compression cyles to pump up,the end result is still the correct reading.

[TwoTired]

The long hose adds volume to the cylinder which changes the compression ratio.
The ratio is: piston swept volume plus combustion chamber volume to final combustion chamber volume.  Or, beginning volume to final volume ratio.
The volume of air compressed in the tester adds to the combustion chamber volume and lowers the compression ratio.
It matters where the check valve is in the pressure line.  If at the spark plug hole, then the peaks made to the compressed volume can add on subsequent cycles to the gauge reading to the peak made in the piston chamber.  If the check valve is at the gauge head, then the volume of air in the hose behaves exactly like enlarging the combustion chamber and lowering the compression ratio, and peak pressures will be lowered at the gauge.

Your compressor has the check valve at the cylinder where the pressure is built (the cylinder) not at the end of the attached hose.

http://forums.sohc4.net/index.php?topic=369.msg476032#msg476032

[Franky]

It's from a bike shop, although I think it's pretty allround (has 10, 12 and 14 mm hoses). It does have a somewhat long hose + the valve at the 'wrong' end. However, after reading TT's link, I'm still pretty happy about my high values and that they are so close together. (Thanks TT).

This is the one I used: http://www.louis.de/_20fda70c6aeeff96c97aa07158e51085c8/index.php?topic=artnr&artnr=10034098
It's from a German webshop, but plenty of pictures

[dave500]

have a close look at the end the valve might be recessed,the guage end has the release valve.

[Duanob]

I see the reason for the bad oil leak. Your o-ring is quite deformed in your last pic. Figure out why it's so mangled before you put a new on in or you will have another leak just as bad. Could be a ill fitting head gasket.

[Franky]

Duanob: Yes, they were quite deformed and also stiff. I have a new gasket set and I think it has new o-rings too.

[Franky]

Hi guys

A little update: The white valve turned out to have a bad seal against the seat. It was quite obvious when looking at the seating surface that about 1/8 of the surface wasn't touching the seat. Also, found more interesting stuff in there: a bent valve and a... well, 'interesting looking pattern' around one of the domes that houses the valves (don't know the right term). I think the engine 'ate' a valvehead once - I'll get pics soon

[Duanob]

I spent the $200 or so dollars and had a machine shop go through and clean everything up, put new guides and seals and button everything up for me. It was nice picking up a clean head all ready to go back on the bike. The bent valve I'm gussing came from not installing the valve cover correctly using the rubber band trick.

As far as head gaskets this time i used a cooper gasket spray and so afr so good no oil leaks!