Author Topic: 1974 CB500 Possible Frozen Engine (Read 5719 times)

lakeboi · « **on:** June 12, 2006, 11:30:11 AM »

Well I bought my first bike this past weekend (and it came with a service manual). The bike is a 1974 CB500 F and the seller thought it had a dead battery and bad ignition coil. I brought it home and kicked it over...that's when the bad stuff happened.

The bike actually fired right up after 20 kicks or so. It ran for approximately 10 minutes (I know I should have preped the bike since it sat for a year). Anyway, after about 10 minutes we heard some clanking and then it stalled. The kick starter will not push forward. I pulled all four spark plugs and noticed that one of the plugs had the gap comletely closed on it as if it was hit by the valve rod. Could this be my problem (an exhaust valve??). I also pulled the timing cover off (where the points are) and tried turning the engine with a wrench. I can move it backwards and then forwards but at a complete revolution it stops again. Is this a situation where I could pour some penetrating oil or diesel down into the plugs?

Any idea what I have going on? Possibly a broken or bent valve? If so, I realize this is going to be a big project and one that I can use my service manual for. My other question is whether parts are available for this beast and where I might find them on the web. Also, would it be feasible to find a compatible motor to drop in it....possibly another 500 or 550?

Dusthawk · « **Reply #1 on:** June 12, 2006, 11:46:23 AM »

I'm just shooting from the hip here but it sounds like a valve either broke and fell into the combustion chamber, thereby stopping the engine from turning, or a valve got stuck at full travel and was hit and bent by the piston. First, you'll have to pull the Head and see what damage is done to the piston, if none, you can probably rebuild the head and be done with it but since you said you heard clunking my guess would be new pistons as well. The cylinder liner should be checked as well.

Good luck,

Jeff

lakeboi · « **Reply #2 on:** June 12, 2006, 12:17:26 PM »

Thanks Jeff,

I'll start at the top and work my way down. Two more questions if I may (and yes...I am NEW to this):

First, I'm not in front of the bike now but according to the manual the cylinder head can be pulled without removing the motor. Is that correct?

Second, Can you point me in a direction to start looking for head gaskets kits and valves?

Much appreciative!

Brian

apormarkos · « **Reply #3 on:** June 12, 2006, 12:41:16 PM »

I'm in the process of finishing up a rebuild of my cb550 which is very similar. yes, you can take apart pretty much the entire motor with it still in the frame. i used an "athena" brand gasket kit. it was pricey at about $130 or so, but seems to be of good quality. you could google it and find one i'm sure. despite one or two missing o-rings (which i ended up getting from honda) i am happy with the kit. if you bent/broke valves or scored your cylinders, you can get them all off ebay, and probably cheaper elsewhere. welcome to the club, maybe i was just lucky, but taking apart a 500 shouldn't be hard at all. good luck to you.
apor

number13 · « **Reply #4 on:** June 12, 2006, 03:48:17 PM »

Rotten luck!!
But, as apor stated, you can get the
entire top end off with engine in frame.
When I got my 500 it was frozen solid, I got
so much stuff off of e-Bay I was considering
asking for a sponsorship. You can get
rebuildable heads for 25 bucks all day long,
both 500 and 550 heads and jugs will work.
If your jugs are toast, re-sleeving is pretty
affordable.

TwoTired · « **Reply #5 on:** June 12, 2006, 04:42:44 PM »

Sounds pretty bad. Take off the tappet adjust covers and watch the valve movement or the tappet gap as you rotate the engine. If you find a really big gap, its a stuck/ bent valve. No gap when tappet not depressed, would be a broken valve.

But, if the spark electrodes are damaged, it's not going to look very good inside.

Word of warning before you buy parts.
Model year 74 there were only CB550 (K0)
Cb500s (all K models) were made for 71, 72, and 73 models years.
F models were all CB550s made for 75,76,77 model years.

A 500 will have 498cc cast into the engine block on the front.
A 550 will have 548cc cast in the same position.

Cheers,

nomath · « **Reply #6 on:** June 12, 2006, 06:01:48 PM »

Quote from: lakeboi on June 12, 2006, 11:30:11 AM

Well I bought my first bike this past weekend (and it came with a service manual). The bike is a 1974 CB500 F and the seller thought it had a dead battery and bad ignition coil. I brought it home and kicked it over...that's when the bad stuff happened.

The bike actually fired right up after 20 kicks or so. It ran for approximately 10 minutes (I know I should have preped the bike since it sat for a year). Anyway, after about 10 minutes we heard some clanking and then it stalled. The kick starter will not push forward. I pulled all four spark plugs and noticed that one of the plugs had the gap comletely closed on it as if it was hit by the valve rod. Could this be my problem (an exhaust valve??). I also pulled the timing cover off (where the points are) and tried turning the engine with a wrench. I can move it backwards and then forwards but at a complete revolution it stops again. Is this a situation where I could pour some penetrating oil or diesel down into the plugs?

Any idea what I have going on? Possibly a broken or bent valve? If so, I realize this is going to be a big project and one that I can use my service manual for. My other question is whether parts are available for this beast and where I might find them on the web. Also, would it be feasible to find a compatible motor to drop in it....possibly another 500 or 550?

I'll follow this w/interest as I have a '71 CB500 whose motor is locked up. A buddy suggested that I (we?) may have a broken cam chain guide/tensioner (the long, tongue like thingy inside) that's jamming the cam chain. I've pulled the clutch and the tranny is free.

doug

csendker · « **Reply #7 on:** June 12, 2006, 07:00:23 PM »

Quote

1974 CB500 F

To follow up on TT's comment, post the VIN number and especially the engine number and then the model can be positively identified. The two numbers should be close, but not exact. Major differences in numbers indicates a likely engine swap at one point or another. As you have engine issues, that number is almost more important at the moment to identify just what you're working with.

Or just look here --> http://sohc4.us/?q=node/29 and let us know...

lakeboi · « **Reply #8 on:** June 12, 2006, 08:14:14 PM »

OK....this is interesting. The frame vin# reads: Made in Japan 10/72 CB500 2112405 (This is what the title says except the year is 1974)

The tag on the engine says: CB500E 2115041 (Yes...it says 500 "E", not "500 "F")

Obviously this means the engine was replaced at some point? I've looked at the links to try to determine exactly what I have but I'm not finding one in the maroon color? Do I have an odd ball or what? I've attached a picture as well.
I'm going to pull the tappet covers tomorrow and try to identify the problem. I appreciate the help....will post my findings tomorrow night.

Thanks again!
Brian

csendker · « **Reply #9 on:** June 12, 2006, 08:26:52 PM »

Quote

Obviously this means the engine was replaced at some point?

I doubt it. That's not so far off. And all of the engine numbers have the "E" - that's how you tell the difference between the frame number and the engine number. Frames and engines were assembled simultaneously on two lines, then mated up at the end. As the lines did not rum at the same pace, the numbers get off kilter, I don't think anyone has an exact match.

I have to dig for the 500 frame/engine numbers/model year info - it's around somewhere, but not at my fingertips.

csendker · « **Reply #10 on:** June 12, 2006, 08:30:50 PM »

Ah-ha! Found it:

Model Yr Product Code Frame No. Engine No.
CB500 (K0) 71 323 CB500-1000001- CB500E-1000001-
CB500 K1 72 323 CB500-2000001- CB500E-2000001-
CB500 K2 73 323 CB500-2100001- CB500E-2100001-

So it looks like you have a '73 CB500-K2, both frame and engine.

TwoTired · « **Reply #11 on:** June 12, 2006, 11:12:35 PM »

I concur, it's a 73 Cb500K2. According to the Honda Motorcycle Identification Guide. (Honda publication)
It been repainted.
Exhaust system replaced.
And the Fork Gaiters are missing. It's either been converted to boots, or it has a 77-78 front end on it.

Cheers,

bryanj · « **Reply #12 on:** June 13, 2006, 05:31:16 AM »

Check out ebay 4648205385 its a head gasket upwards lot with a buy it now of $25 and $30 shipping also there are top and complete sets on ebay for about $25. You may have a broken camchin for which Honda say you need to split the bottom half but you can link and rivet a new chain in. I would be interested in the "build date" on the vin plate on the RH side of headstock for my "list"

lakeboi · « **Reply #13 on:** June 13, 2006, 10:03:21 AM »

OK....not to sound like an idiot but when you say "head gasket upwards" I assume that has everything you need rebuild the head. I don't have my service manual in front of me right now (though my nose has been buried in it lately). It would have the head gasket, and the top end gaskets? Would it also have pistons and valves? Sorry...maybe I need to read the manual a bit further. Also, a 1972 head will fit a 1973?

BryanJ, Check a few posts prior....I put the vin# and build date....I believe it was October 1972.

Are there any other online resources for this bike other than the service manual that might walk me through taking apart and analyzing the problems I might have? I'm going to begin looking into the things that have been mentioned tonight....just like to read stuff while I'm not working on it.

Thanks!
Brian

will post a picture of the vin plate later as well!

lakeboi · « **Reply #14 on:** June 13, 2006, 09:40:47 PM »

WOW....this is slow going. I haven't even gotten the cylinder head off yet. These phillips head screws are a pain in the butt. Is there any other way to check the cam chain other than pulling the cylinder head off?

Many thanks!

BTW....I'm putting my MBA on hold while I finish this!

Brian

seaweb11 · « **Reply #15 on:** June 13, 2006, 10:13:12 PM »

Are you using an impact driver?

If not get one and all will come apart with a bit more ease.

bryanj · « **Reply #16 on:** June 14, 2006, 07:08:26 AM »

The bits i was talking about are The head (complete with valves) cam and cam cover so everything MECHANICAL you could possibly need. All 500/550 heads and cams are the the same Late top covers are better. also a seller "triton"? has some top sets for about $5-10 at the moment

puppytrax · « **Reply #17 on:** June 14, 2006, 10:02:01 AM »

While rebuilding engines is always educational, you haven't mentioned looking for the cause...just fixing the effect...

What happened to it? Did it have oil? Was there any indication of it running more slowly before it died? Any smoke? Any misfiring? Any "tinging"?

As to motors...I've been offered a couple of 550 engines, they seem to be available for ~$200 + shipping (or you pick up) complete. Now, if it was me...I'd get a 2nd engine and go over it (on the bench!) before I put it in...and rebuild (or not) the first one when I had the chance/change...in fact, that is exactly what I plan on doing, if my 500 gives out (no guarantees on 33+ year old motors!)

lakeboi · « **Reply #18 on:** June 14, 2006, 10:47:39 AM »

There was no indication of smoke. I wasn't riding it at the time....just idling and attempting to keep it running. Just before it locked up it sounded as if it was flooded....started to bog down. Then there was some clanking and it stopped. I can move the crankshaft a full rotation in either direction but then it locks. If the cam chain came off partially I wouldn't think it would move at all, so I was thinking maybe a valve.
The bike hadn't been ridden in over a year and there was oil but it certainly wasn't prepped to be started after sitting for so long.

I realize I could pick up a new motor but was thinking I could also pull the top end off and see if there is an easy fix in store. If not, I'll probably look for a motor that will at least turn over. In your opinion, is a motor replacement easier than rebuilding the top end?

Brian

puppytrax · « **Reply #19 on:** June 14, 2006, 12:49:25 PM »

Quote from: lakeboi on June 14, 2006, 10:47:39 AM

In your opinion, is a motor replacement easier than rebuilding the top end?

I've never rebuilt the 500/550 top end, so I really can't say...but I've pulled two engines out and put one in, with only removing the oil filter (leaving the sump and exhaust studs intact), and I've cut the time involved down considerably...but I cheat; I use a chainfall (just a little one!)...

Just on your comment about the engine bogging before dying, I would suspect the piston in at least one cylinder seized...if the cam chain had snapped, it would have died instantly...a valve bending or breaking sounds likely, but again *why*

The spark plug being mashed sounds bad...something has to be rattling around in there to do that...

It just sounds very expensive to me...a replacement engine and some routine maintenance on it sounds a lot easier...

There seem to be a lot of these machines coming into the salvage yards every day now...

In any event, good luck to you! Whatever path you choose will be very educational!

lakeboi · « **Reply #20 on:** June 14, 2006, 08:50:05 PM »

ok...maybe I found my problem. I'm following the cylinder head removal instructions from the Clymer manual. Step 4b talks about removing the chain tension holder by "unscrewing the bolts and removing the tension "slipper". Does anybody recognize the picture below? I have only removed the cylinder head cover.

Is it possible this chain tension holder fell off and down into the cam chain? If so, any ideas how to get it out? Is this possibly what is locking up the motor?

Thanks!
Brian

TwoTired · « **Reply #21 on:** June 14, 2006, 10:27:22 PM »

No. It looks okay so far. Take a look at pg 24 & 25 of the Honda Shop manual for the CB500.

To take out the tensioner, remove the nut on the adjuster below the intake manifold on the back of the cylinders.

However, you should leave it in and make the tensioner slack so you can remove the cam first.

The Clymer is giving you pictures of several different engines, and this is confusing you. Better to use the Honda manual.

Cheers,

lakeboi · « **Reply #22 on:** June 20, 2006, 10:14:02 AM »

OK....seem to have found the problem. Anybody have any idea how bad this looks? Appears I'll need a new piston and a new valve. Is it ok to replace just the ones that are damaged? Also, looks like I'll need some work on the head where the valve seats. This is probably too much damage to repair with the valve lapping compound that the Clymers manual talks about?

Any help would be greatly appreciated. BTW....anybody ever seen one of these valves break like that before? The pistons appear to be moving freely so I'm guessing no damage to the bottom end.

Thanks!
Brian

lakeboi · « **Reply #23 on:** June 20, 2006, 10:14:36 AM »

Another Pic

lakeboi · « **Reply #24 on:** June 20, 2006, 10:15:03 AM »

Another

lakeboi · « **Reply #25 on:** June 20, 2006, 10:16:04 AM »

Lastly...

TwoTired · « **Reply #26 on:** June 20, 2006, 12:03:52 PM »

Look for marks on the cylinder wall, too.

Find the bits of piston where that hole is that are likely in the bottom end somewhere. Hope for a single piece laying in the bottom pan or hanging on to the inside of the piston.

Best case:
New Std size piston and rings.
Hone cylinder
Replace entire head with used cylinder head assembly
New gaskets/seals
Reassemble and run.

Worst case:
Metal bits from hole in piston, valve bits etc. lurking in lower end jam into gears, or something. Trashing lower end.
Cylinder wall scratched or cracked.
Unavailable std size pistons/ rings.

Other Options:
Swap entire top of motor from a donor engine. (cam. cam cover & bits optional.) Still need gaskets/ seals)
Swap entire motor. (find a 550, along with the clutch cable and clutch cable engine mount, methinks.)

Bummer...

merc2dogs · « **Reply #27 on:** June 20, 2006, 02:08:27 PM »

That's what I was afraid you'd find in there.
double check the cylender walls make sure there's no damage to them,
If you want to keep the original head, you can normally have new seats installed, and depending on the depth of the gouges in the head either sand them smooth, or have them filled with weld.
new piston and valve should set you straight after that.
If you have to buy a new piston, may as well go for all 4 pistons and rebore it to the next oversize.

Otherwise pick up a known good head and piston and install them

whichever way you go be sure to clean out the oil pan and change filter and oil

Of course if you can pick up a wrecked bike cheap you could always swap engines, unless you live in a state that keeps track of them.

Personaly, I'd take the first route with new pistons/gaskets/bearings, it will almost be a new bike.

ken

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Author Topic: 1974 CB500 Possible Frozen Engine (Read 5719 times)

lakeboi

lakeboi

apormarkos

nomath

lakeboi

lakeboi

lakeboi

lakeboi

lakeboi

lakeboi

lakeboi

lakeboi

lakeboi