Topic: Engine Experts, Help!

[motorcycleclaude75]

Hi All,

My weekend wasn't so good    The weather was perfect but my motorbike is not so good.

First some background on my bike, it's a 1972 CB 500, original motor (as far as I know) with about 50,000 miles on it.  Last fall, I got the carbs rebuilt and sychnronized and it has run perfect for the last 3000 miles.

Over the weekend I took a trip, about 200 miles to my parents place.  It's 2/3 highway, the rest backroads.  It was a warm evening and about 1 hr from my destination, I noticed the bike was laking power but since it was quite windy and I was also wearing earplugs I couldn't hear anything abnormal.

But as soon as I took the highway offramp, I noticed the bike was running like crap.  It would barely run (wouldn't idle) on it's own and was backfiring from the right side.  I limped the bike to my brother's place.

Here's what we found:

Cylinder 1: plug was light gray to almost white
Cylinder 2: same as 1
Cylinder 3: Ceramic of plug has white ballls stuck to it   
Cylinder 4: Electrode coverd in thick black(soot?)   

Also it used a lot of oil, about 1 litre, during the short trip.

We replaced all plugs, check points, all plug wires, fuel filters.  Bike still runs like crap, backfires on right side and sorta sounds like a sucking sound from pipes.

We didn't have a compression tester so we haven't tested this yet.

Anyways, I managed to get the bike home since I could still get the bike up to 65mph.  I didn't have much choice so I took a chance and made it home.

So what do think is my problem?

[Steve F]

Running WAAAAAAAY too lean.  Probably fried an exhaust valve or two.  Get the compression check done, and find out why she's so lean.

[eldar]

Well 1 and 2 are certainly running lean. 4 seems to be getting no fire as shown by the sooty build up or way too much gas, maybe oil, but I think gas.

#3 is what concerns me. You have balls of something stuck to the insulator?! That could be a very big concern. I hate to say it but you may want to pull the engine or at least pull of fthe tank and pull the plug and try to see what you can.  Last time I saw something like this was when a piston burned thru but that was black deposits.

I hope someone else has better news for you. It could just be the plug is falling apart butthen why would the plug fall apart?

[Boomologist]

That sucking sound is an indication of a burned or stuck exhaust valve.
Your symptoms indicate major carb problems, also.
Are your exhaust pipes Blue where they make the first curve out of the engine? Especially #3?

[Lumbee]

...the little "balls" just sound like deposits from running way lean.  I'd do the comp. test first...if that checks out OK, then go to your carbs.  What are you jetted at?  What exhust/airbox are you running?

[motorcycleclaude75]

Thanks for your input.  I'll keep you all posted, I will be doing a compression check tomorrow.

Claude

[Duck]

I suspect partially blocked fuel flow to carbs leaned it out.
Check blocked tank cap vent, screen on pickup in tank, screen in petcock bowl(if it has one), add on filter, screens on float needle seats(if it has them)

Check the compression.

If you have oil coming out the pipe connected to #3 you've got a hole in that piston. Deposits on that plug are very likely bits of melted piston crown. Easiest way to look for damage is with a mirror and a flashlight. Take the plugs out, look in the holes, turn the engine over until you can see the tops of the pistons. If it looks like you have a hole, a bamboo kabob skewer or chopstick will confirm.

OK, so it sounds bad. It isn't. You can find a low mileage block and pistons on this forum or ebay. Get it from someone who nows what they are doing and has kept track of which piston goes in which hole. Best to pay extra and get from someone who can measure and confirm everything is in spec. I got a setup like this for my z1000 for $60. A buddy got for his XS650 for $70. Takes some looking and patience but the stuff turns up. Else, if you have the $ and are in a hurry, add a big bore kit.

[motorcycleclaude75]

Hey all,

Well, I did a compression test, here's what I found.

Cyl 1: 90
Cyl 2: 90
Cyl 3: 80-85
Cyl 4: 10   

I thought to myself, this can't be right. I rechecked cylinder4 at least 3 times, same thing, barley registering on the gauge.

I did the old oil test in cylinder 3 and 4.  Cylinder 3 went up to about 95 so used rings, but cylinder 4 only went up to about 30, so if I'm interpeting this right, my rings are gone.

I'll  be doing a second test since light was starting to fade but I think I'm in for some big bucks.

Anybody know the approximate cost to redo the whole engine.  I've seen different kits but which one works best with existing cam, carbs etc.

Thanks Again

[Steve F]

One question that comes to mind is did you do the compression check with the choke off and the throttle WIDE open using the electric start?  Or better yet, remove the carbs all together.
If you did do it this way, well......sounds like a top-end rebuild 

[Lumbee]

75, looks like u'r in for some engine work, but I wouldn't call it big bucks.  1st thing is go ahead and pull the engine, get the top end off, and see what you've got going on.  I tend to think the #4 is a valve situation...either way with the compression low all the way around I'd plan on new rings.  Check out the valves and see how they look.  You may just need valves on #4, or possible not at all.  Either way if u'r smart about it I could see you getting out for under $300.  Not sure if you consider that big bucks or not?    I'm a pretty cheap bastard, and I don't see that as breaking the bank.  I'd get u'r rings NOS, but the other parts I would scrounge together from Ebay, and the wanted section of this board.  The other option is to look for a complete engine...there are 500's and 550's in the for sale section now.

Good luck and keep us posted...u know pics of the inerts is always nice... 

[TwoTired]

Well, I did a compression test, here's what I found.

Cyl 1: 90
Cyl 2: 90
Cyl 3: 80-85
Cyl 4: 10   

I did the old oil test in cylinder 3 and 4.  Cylinder 3 went up to about 95 so used rings, but cylinder 4 only went up to about 30, so if I'm interpeting this right, my rings are gone.

No, you probably have a valve issue more than a piston /ring issue.  You can expect a slight increase and "evening" in compression across the bank with additional oil, as oil doesn't compress like air and it seals a dry cylinder better than rings.  But, disparities like that are some other compression loss.

I think I'm in for some big bucks.

Define big bucks. 

Pull the head and cylinders off and have a look inside.  You can do this with the engine in the frame.  Make decisions based on what you find inside and what you can find as replacement parts and/or engines.

Post pics, and we can help guide you.

Cheers,

[Duck]

Hey all,

Well, I did a compression test, here's what I found.

Cyl 1: 90
Cyl 2: 90
Cyl 3: 80-85
Cyl 4: 10   

I thought to myself, this can't be right. I rechecked cylinder4 at least 3 times, same thing, barley registering on the gauge.

I did the old oil test in cylinder 3 and 4.  Cylinder 3 went up to about 95 so used rings, but cylinder 4 only went up to about 30, so if I'm interpeting this right, my rings are gone.

I'll  be doing a second test since light was starting to fade but I think I'm in for some big bucks.

Anybody know the approximate cost to redo the whole engine.  I've seen different kits but which one works best with existing cam, carbs etc.

Thanks Again

HUH???

If adding oil brings compression up to almost normal then rings are bad.
If it makes no diffeence, then it's valves (clearance not right as adjustment issue, or damaged)
If it makes some difference but no where near normal, then it's BOTH valves and rings or not likely without lots of confirming  mess, head gasket.
If zero compression and oil flowing out exhaust then it's PISTON HOLE!

"redo"

top end

$200 to $2000 depending on patience, if you do your own work.

minimum
rings $160
hone $40
gasket kit $60
lap valves $80
labor $400

rings, pistons, bore sleeves, add electronic ignition, new clutch parts, new valve springs, grind valves and cut seats...atarts adding up fast for parts and labor

[motorcycleclaude75]

Hi All,

Just a quick update.

I ended up taking the engine out and bringing it to a shop.  I figured that I don't have the time and tools to do the job.

It will cost me more but I should have a good engine for many years.  The engine needed to be refreshed anyways, I thnik I was ridng with low compression for many years and didn't know it.

Once I get it back, I'll let you know how it went.

Claude

[smashme33]

 Let us know how it goes. Hope to hear that you're riding that bike soon!