Topic: First timer top-end rebuild gone wrong, yippee! Ugh...

[markreimer]

Measure the piston skirt and do the feeler gauge measurement where the arrow is. You may get a different reading on the piston to bore clearance. Also check the bore in different spots to be sure its not egg shaped.   

I tried there, but the feeler gauge wouldn't fit at all. That's the smallest feeler gauge I have at the moment. I figured if it could fit in on the sides, it didn't matter if it could or couldn't fit where your arrow is. I guess it would tell if the cylinder isn't round anymore, but does that matter much if I'll be boring it anyway? I'm going to be doing the second oversize bore, as I can get those pistons for cheaper than the first oversize, so that's a fair amount being taken out. Should take care of the out of round?

[markreimer]

After doing a search through the forum for measuring valve guide clearance, I found this video linked:

I tested it using the second method but never divided my number by two, like I asked about earlier. So it looks like my guides actually are within wear spec, at 0.0025. Very sweet, that will save me some dollars. Ordered the second-oversize pistons from Cycle-X. Next report will be during reassembly time!

[flybox1]

Be sure to throw on a new set of HONDA guide seals 

[Vinhead1957]

I wasn't sure with that graphic either. The video is clear.  The piston bore spec is done the same way as the first method.  Keep reporting your finds.  I have an engine ready to tear into but need a little push. 

[markreimer]

Will do.

I measured the piston bore with a telescoping t-gauge. Definitely worn. I ordered the Cycle-X second-oversize piston kit. It comes with pins, clips, rings and pistons for $200. Plus they have a complete top-end gasket set on sale for around $60. Hard to beat that. They said it should be here in about a week, so I should be able to start assembly around Christmas/new years time.

[flybox1]

Read this thread before you start putting everything back together 

BrandEn's Leak Free Top End thread....
http://forums.sohc4.net/index.php?topic=107040.0

[markreimer]

So I tried installing the cycle x rings into the cycle x Pistons this evening. The three piece oil rings fit  fine and the top rings do as well but the second rings will not fit in any of them. I test fit them first by rolling the ring around the piston but once I snap them on, nothing.

Any advice? I assume they need to be loose enough to turn freely, not jammed tight right? I already set the end gap on all rings. Only the ring groove is an issue now.

Is it common to file the piston groove? Seems a bit shoddy.

I also buried a box cutter into my thumb while working an old chunky piece of gasket off and now my block has a nice red patina... Waiting for stitches at the moment. I am a dummy.




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[Vinhead1957]

If recheck part numbers and have cyclex on the phone. Should be easy as pie. The rings need a little free play. Especially when things heat up.

[markreimer]

False alarm. Everything is fine. The cycle x rings are real stiff and during the install I must have created a tiny gouge and also got some grit into the groove.  After some extensive cleaning they spin freely. Perfect fit. Next up, install Pistons and slide the block on.


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[markreimer]

Picked up a $10 piston ring expander tool today. I was able to fit all the rings to the cycle-x pistons in about ten minutes with zero fussing or binding issues like I had previous.

Just goes to show that it's always worth buying the right tool for the job.

All four pistons are ready to go. tomorrow I'll install them and get the block on. I also picked up two ring compressor tools, so I'm hoping for a quick and easy install.

Next up is the head. I cleaned up the valves, but am concerned the exhaust valves may not be suitable for re-use.

[markreimer]

Ok, had a great morning in the shop today. I did a final clean and lube on the pistons/rings, then first tried inserting them all into the block, then lowering the block onto the rods. I thought it would be easier and less risky in terms of breaking a ring. I quickly realized that was not the case and decided to start over and do it the 'normal' way.

Glad I did, because it was a breeze really. I just used my finger nails and a small flat screwdriver. It was actually much easier than I was expecting (this is my first time doing this).

Next up is the head. I'm interested in hearing some opinions here..

The eight knock pins that sit in the cylinder block do not sit flush with the top of the block. I've never had a head gasket leak before, but I've read a few times here that if the knock pins aren't sitting flush, there is a big risk of a leak or lost compression.

Some say just leave the pins (and the rubber seals) out entirely as these passage ways are not under pressure (oil drains via these passage ways). Others say that leaving it out is just asking for an inevitable leak.

I have new rubber seals, so i'm inclined to just use them, why not eh. Any reason why I couldn't just grind these down a bit so they sit flush?

The actual rubber seals stick WAY past the top of the block. (see the photo of old and new next to each other) Am I correct in presuming this is intentional, so they are compressed when the head is torqued down? The old rubbers fit perfectly, though I assume it'd because they were sandwiched for a while.

Ok, last question... My cycle-x head gasket doesn't seem to sit flush on the block. It's like there's a bit too much material right in the centre of it, which you can see in the photo. Is this typical of gaskets to not fit 100% flat, and it sorts itself out when cranked down? Or is it possible I've got a flawed gasket?

[faux fiddy]

,
I just installed rings, they also had the "R", for up side. They didn't have a 1 or 2 designation, the top ring had a gray trim

+1. I know there is at least one thread here where a fresh rebuild smoked too much to ignore. When it was opened back up the rings were upside down.

Ok, last question... My cycle-x head gasket doesn't seem to sit flush on the block. It's like there's a bit too much material right in the centre of it, which you can see in the photo. Is this typical of gaskets to not fit 100% flat, and it sorts itself out when cranked down? Or is it possible I've got a flawed gasket?

Tough call on that, but a bit of yamabond can't hurt. It should flatten out- it has no choice.

[markreimer]

,
I just installed rings, they also had the "R", for up side. They didn't have a 1 or 2 designation, the top ring had a gray trim

+1. I know there is at least one thread here where a fresh rebuild smoked too much to ignore. When it was opened back up the rings were upside down.

Ok, last question... My cycle-x head gasket doesn't seem to sit flush on the block. It's like there's a bit too much material right in the centre of it, which you can see in the photo. Is this typical of gaskets to not fit 100% flat, and it sorts itself out when cranked down? Or is it possible I've got a flawed gasket?

Tough call on that, but a bit of yamabond can't hurt. It should flatten out- it has no choice.

Thanks. It's odd, there is definitely no markings on the rings at ALL. I used a magnifying glass, and got two other people to look. A quick search through the forums turns up comparable results. It looks like the Cycle-X rings are not designed to have a top and bottom, they are the same.

Regarding the gasket, I've got some yamabond handy, which I had intended to use anyway, so I'll give that a go.

I also found this thread re: knock pins:
http://forums.sohc4.net/index.php?topic=81643.0

I'm going to shave the knock pins down just a hair so that they don't prohibit the head from sealing properly. The only thing I'm not sure about now is if those rubber seals are abnormally tall or not. Seems like quite a lot of rubber to compress.

[markreimer]

Another productive day in the shop.

I got the engine all back together. After giving the valves another cleaning with a brass brush, I gave them a real thorough lapping, which removed all traces of the scratches I discussed earlier.

During the rebuild, I ended up grinding the metal dowels down just a hair so the head could sit flat against the cylinders without a gasket. Then I installed the rubber seals around them, gaskets, and the thinnest layer of Hondabond in a few places as I deemed necessary.

I finished assembling the head, using Hondabond on the rubber pucks and the front of the cam cover. New o-rings and gaskets everywhere, valve seals as well.

After that, it only took me 2 hours to get the engine back into the frame and everything else bolted back together. On Sunday I'll fill it back up with oil, prime the oil pump and give it a try. I don't have a compression tester at the moment, but I'll try to get my hands on one first. I'm curious what the readings will be after the rebuild.

And if you notice something nice in the background, that's my latest acquisition... an '85 r80!

[Trad]

Really nice work! How many miles were on your bike before the rebuild?

[markreimer]

Really nice work! How many miles were on your bike before the rebuild?

Not that many, maybe 30,000. When I bought the bike, it had around 16,000 miles on it. The previous owner had just done a top end rebuild, though I have no idea why. I think he was planning on doing a total rebuild of the bike, just as a way to pass the time. He was an older, retired fellow, used to ride these back in the day.

Anyway, he sold it after he replaced the rings but I don't think ever fired it up for more than a minute or two. The bike ran well for about two seasons, then started fouling plugs occasionally, then more than occasionally... then blowing blue smoke out the left tail pipe.. I thought it was bad valves, so I got the valve seats recut, new guides and seals, etc. Nothing changed! That was a rude surprise. So I rode it on some shorter rides, fowling plugs, having an overall not fun time. Now I'm doing the top end properly - new pistons, rings, etc. Hopefully this does the trick and I can get it back on the road!

[flybox1]

Its coming along nicely, Mark!
I soak-primed my oil pump before i installed it, and even after several attempts to get the oil light to go out w the kick and stater, it wasnt until I just started it, that it did go out.  And it went out right away.
Pour 1/3rd quart into each of the #1&4 intake tappets, and the rest of the bottle into the R side galley plug hole while the bike is on the side stand before start up.  You should have pressure in no time.

[markreimer]

IT LIVES!

I popped the engine back in the frame, this time with only one extra pair of hands. It's much easier getting the engine in than out it seems.

I spent Sunday morning getting the bike back together and priming the oil pump. It took a lot longer to get the oil to flow than I expected. I hit the starter in 2-3 second bursts until the battery died. Then hit it with the kick starter. About 20 minutes later, oil started to pour out of the right-side galley, and then a few seconds later started squirting out the top end. Good!

I charged the battery and gave it a go - at first it wouldn't start. It would catch for a second but quickly die. Then it finally turned over with a roar. There was a lot of white smoke at first, but it cleared up within a minute or two. It needed full choke for the first bit, but I was able to back it right off a minute or two later and it idled nicely at around 1,100 rpm.

Here are two videos - one from behind to hear the nice rumble, and the second from the front. You can see the bike hesitates when I snap the throttle a few times, which I'm thinking is a dirty carb or old fuel issue. The bike hasn't been run in about five months or so, and I forgot to put stabilizer in it. I'll empty that out, give the carbs a cleaning and use fresh fuel in the spring.

So now I've just got to wait patiently for the snow to melt so I can give it a proper test. Let me tell you, it really sucks to not be able to take this thing for a ride now.

[flybox1]

Nice work!
As the bike warms to OP temps, the stumble should diminish, but if it doesnt, you'll need to check your A/F mixture at idle up to 1/4 throttle, and adjust accordingly. 

[markreimer]

Took the cb750 for the first ride post-build yesterday. First impressions - HOLY CRAP it's better than before! It is smooth, powerful, fast.. Sounds beautiful, no smoking (well, at first it smoked on startup, but that'll be from burning off the oil I coated the cylinder walls in during the build I suspect), it was wonderful.


Until... I stalled out 10km into my ride, and there was no juice in the battery to turn the starter...?? I had left with a fully charged battery and it discharged in ten-15 minutes. I still had all my lights working though. One kick and the bike fired right up, so I headed back home. I shut it down and tried the starter again - nothing. Hit it with a charger for 5 minutes, started immediately.


So, something is obviously draining my battery. I've never had any electrical issues on this bike before, so it's something that is happening as a result of the rebuild. I checked all the 'freebies' - Battery connected properly, fuses were all good, the two big connectors running from the alternator seem to be in good shape, no loose connections there...

Electronics are my biggest weakness. Other than checking that everything is plugged in the way it was pre-rebuild, I'm not sure where to start.

Any tips? It's killing me to not ride!

[flybox1]

http://forums.sohc4.net/index.php/topic,1012.0.html

It's all right there...

[Vinhead1957]

Go to the charging troubleshooting guide in the faqs.   Do you have original reg/rec.?   My guess would be the two wires that are inside the chain guard. Green and white. One should have continuity to ground ( green ) the other is 12 v when calling for charge.  The regulator controls that.

[markreimer]

Thanks for the tip, should have looked for that first!

I'll check those two wires. That was my first guess too - first thing I did was remove the sprocket guard and look at those wires. When I first bought the bike it didn't charge for that exact reason - the guard pinched a wire when the guard was last installed and grounded it. I didn't see signs of it yesterday but I'll take a closer look, easy to miss.

But overall I've got to say I'm super happy with how this motor is running. It's only just being broken in, but no leaks so far.

[markreimer]

Problem solved. Looks like I got away easy this time. I found a small wire connector coming off the starter relay (I believe that's what it is - positive terminal from the battery connects directly to it) was not plugged together properly. Possibly shorting out to the frame. I pushed them together and checked with a voltmeter:

Ignition off: 13.08 volts
Ignition on, killswitch in 'start' position: 11.5 volts
Engine running: 13.5 volts
3K RPM: 14.75 volts
4K RPM: 15.5 volts, highest voltage I could record.

I drove it for about 15km of stop/go city streets over to my friends place, then shut it off and let it sit for an hour. Checked with ignition off: 12.5 volts. Fired up instantly, and recorded the same running and charging voltages. Seems like all is well now. I'm leaving it for a few days with no battery charger/maintainer on it to confirm it'll start easy after sitting for a while. If it does, I'll consider this case closed.

[markreimer]

Sadly I have the need to ressurect this old build thread. It's been about 5 months since I rebuilt the motor, haven't had a chance to break in the motor till this week.

My #2/#3 cylinders aren't consistently firing due to fouled plugs, and the engine feels like it's getting really 'tight' after it heats up - is it starting to seize??




Here's what's happened:

At first I couldn't get it to start. It would crank away but never 'catch'. First I checked the carbs - clean as a whistle. Cleaned them again anyways. No luck. Then I thought of the gas - it was over a year old! Changed that, still no luck. Then I checked the plugs - they were soaking wet with gas. Put new plugs and blamo - fired right up.

I took it out on the hwy and it ran like a champ - pulled super hard and smooth right up to 100mph.

When I got home after riding about 50km of hard and fast riding, I let it idle on the driveway. I saw a bunch of white smoke coming out the breather hose and from #2 and #3 spark plugs, with oil leaking out of the valve cover. WTF? Shut it off, checked the oil and it was overfilled by 1cm. Duh. Drained it to proper levels and the smoke went away.

Next day I went to start it up and #2/#3 wouldn't fire. I pulled the plugs and they were black and wet. I figured it was from yesterday's overfilled oil, so I replaced them and went for a short 10km ride to work, and another short ride afterwork.

The next two rides the bike started up fine and ran smoothly, up till tonight. The bike had sat a few days, started up fine, ran great across town. I helped a friend change his brake pads, and after went to start up my bike. #2/#3 weren't firing. Crap, I don't have any more plugs. Time to lug it home. Halfway home the two cylinders started firing again, guess the heat dried out the wet plugs. Ran fine all the way home.

After I shut it down, I tried starting it again. The starter could hardly turn the engine. Sounded like the battery was dying. But even with the kick starter it was really tight. Hmm... not good.

I pulled a few tappet covers to check for oil. #1 and #4 exhaust first, oil splashed out. #1 and #4 intake tappets - no oil splashing out. Uh Oh. Should I be seeing oil flying all over the place from the intake tappets as well? I haven't checked the middle cylinders


Any thoughts as to why I might be fouling plugs? It only happens when the bike is sitting. They don't die while riding. And how much resistance is normal for a rebuilt engine?