Topic: Bent / Broken Valve - Cause?

[jakec]

Ha! Right? The one thing that I can say that I do remember about the bike was that the valves sounded more “pingy” than “clacky,” if you know what I mean. A little louder and sharper sounding than my 350. It may be possible that they valve clearances were too tight.

[bryanj]

There is 1 head on ebay UK from an 11000 bike but its £110 gbp(guess about $150) and then there is postage

[jakec]

Ok so I have dropped off the head at the machine shop near me and hear back from them.  Today I will order parts. Here's what they said.

They removed all valves and inspected guides. They said that I would be totally fine just installing (1) new valve and guide, but would be better off replacing all (4) valves, and (2) exhaust guides. Ok so what I think I will do is get (1) exhaust guide and (2) exhaust valves. A mixture of the advice I got from them and from here.

Kibblewhite valve guides are $15 each. but they are all 0.01 over spec for some reason? Also they do look different than the parts diagram (no washer / base)? I guess they reuse that part?

I did find an NOS one for $25.

https://l.facebook.com/l.php?u=https%3A%2F%2Fwww.ebay.com%2Fitm%2F153885387081%3Fepid%3D1711809061%26hash%3Ditem23d448a949%253Ag%253AUzQAAOSwN~dehebG%26fbclid%3DIwAR1uMWeD-pdlaIcb0VCZVUVpw5dSSmpfR27sA4Jfl-mVPJutcqIPYbPYvuY&h=AT2LxN6YJEIpgjN9fGyHEpnteMABgrq8Z4BXdBeDNWzchBwA0oC3gHhyn3UJSvVQ3qNqxVsBgX1VYxJ2scPhzEi6MBa6garH6ExfS_THkyQyguEgHBo0N3yJ_flV_nh6Nqg9JNpOJ4d9BbSk4msLXw

Need 2 of these new valves at $27 each:

https://l.facebook.com/l.php?u=https%3A%2F%2Fwww.ebay.com%2Fitm%2F324452860568%3Ffits%3DModel%253ACB350%257CMake%253AHonda%26hash%3Ditem4b8ae5c298%253Ag%253A6nMAAOSwlSRgALtR%26fbclid%3DIwAR28zDuAkOTB8oNtrB_pX6Qiu-CiX13lEfLbqNF4XfGdW-gMrQl8BQZZuT4&h=AT1O_6-gCcyge5uF7bObhb2P-xQ2PLL9rD7aulnOzFWfh5pmikIauWsOFQ8W328PJrSL-4Q-RFX__HbqCHQa7tRsWoZFLTjEKgjQ5GMWzcFtuyPuR1pY4pWU_3YdJ7XvWYFonznZYM6_m4mlvYvu_A

Then I just need a top end gasket kit, 4into1 has a total overhaul kit for $50.

[754]

Valve giudes often come in a few oversizes. Due to the BRUTAL methods used by most, while removing them...it ysually scars or wears the bore it sits in...... that can rssult in puffing oil.
 If you have a drillpressm and can make a holding devicem you can drill them out, snap the heads off, and drive them out towards the chamber. .. clean hole. Most..... even  shops ..l wont do this.

[PeWe]

Stock steel guides last longer than bronze.  Especially on a CB750.
Might be same on other Sohc's.

[jakec]

Ended up with 2 new exhaust valves and 1 new OEM / NOS guide. Plus gasket set from 4into1.

Had the work done at the machine shop as well as decking the underside of the head. I kept the old pistons and rings in. I confirmed ring installation was good and checked rotation. I have reassembled the engine now (holy cow, so easy compared to sohc4 engine. so many fewer parts!). Engine is in frame just waiting for a couple tools. Back tap tool for #2 plug bore, and chain breaker (had to get new DID chain because idiot PO put an X ring chain on the bike).

Will update... any break-in advice appreciated.

[HondaMan]

Ended up with 2 new exhaust valves and 1 new OEM / NOS guide. Plus gasket set from 4into1.

Had the work done at the machine shop as well as decking the underside of the head. I kept the old pistons and rings in. I confirmed ring installation was good and checked rotation. I have reassembled the engine now (holy cow, so easy compared to sohc4 engine. so many fewer parts!). Engine is in frame just waiting for a couple tools. Back tap tool for #2 plug bore, and chain breaker (had to get new DID chain because idiot PO put an X ring chain on the bike).

Will update... any break-in advice appreciated.

Just keep it below 5000 RPM for the first 100 miles or so, then wait until 1000 miles before trying for redline. Change the oil at 300 miles and 1000 miles, too.

About the "direction" of the valve clearance adjusters: if they are set the 'wrong' way it just makes the rocker move inward (toward the cam) slightly which causes the wipe pattern of the rocker across the top of the valve stem's tip to shift inward (toward the cam) slightly, instead of centering it across the whole tip of the valve. In real life this seldom matters, but at high RPM (road racing, long interstate trips, etc.) it can cause extra loading of the stem against the outboard side of the valve guide. Over time this will cause increased wear on that guide, but we are talking about thousands of miles, here...

[jakec]

Everything is going fine so far with about 25 miles on it. The only thing so far is a bit of an oil leak from the right side cover / cam shaft holder. It seems to be coming from the gasket area. Both rocker shafts have their O rings.

[bryanj]

Common leak DO NOT be tempted to ue gasket goo on there just clean grease to soften the paper a bit

[jakec]

Re: the leak are you saying take the cover off and add some grease to the gasket?

So yesterday apparently the bike started running one one cylinder and she had to limp it home. I wasn't there but this is what she told me. It started backfiring and feeling weak. Running rich. So she rode it home slowly on one cylinder, but it would also randomly run on both cylinders for a second or two. She doesn't know which cylinder was running because both pipes were already hot from the ride. #1 plug is dark but not fouled, #2 plug looks normal.

I looked at it and valves are all still moving thank god, and there is compression and spark. Spark is strong but yellow, not blue. Fuel filters are full of fuel so I assume good fuel flow. Full tank. Good battery. Brand new coils from 4into1. OEM condensers and points.

At this point I'm thinking it's probably the condensers, any other ideas?

[jakec]

I have not tested battery voltage.. perhaps battery is low due to riding at low RPM.. but headlight still works.

[bryanj]

Try  running with the points cover removed and also check no wires in there touching the case

[cat]

Checked the battery and it was showing 11.9v. So we swapped in a different battery, spark turned blue, and it's running OK again. I guess that's what happens when you ride 50 miles under 5k RPM!