Author Topic: '73 cb350f siezed barn find! (Read 18220 times)

574hondarider · « **Reply #150 on:** March 27, 2020, 09:35:40 AM »

Thanks everyone. I've been emailing Mark and he thinks that all 4's will have slightly egg shaped cylinders and need a bore to correct the issue. Mark has used CI and had good results after a bore, I didn't bore just honed as my power sport machinest said they looked and spec'd fine according to honda's manual. He builds race engines for team honda motorcross so I took him at his word......

My compression tester reads 59, 60, 60, 61. I know that number seams off, but I believe it is the large diameter hose that's on this tester (my other cb350F reads 60s and runs fine).

So now I am debating about doing the first bore, and sourcing nos honda rings and pistons. If I do a .25 over, can I use a standard head gasket, and will it require rejetting (I just purchased and installed all new keihin stock jets lol)?

Thanks

WhyNot2 · « **Reply #151 on:** March 27, 2020, 10:18:59 AM »

Someone told me that the head gasket is meant to go up to the max bore, so you should be fine with a bore and using the stock head gasket.

Can't remember who it was, but they are a reputable forum member, either of this one or some others I look at.

I did the bore to .50 mm and haven't had any issues, other than me being old, fat and ugly, and lazy to boot.

Wasn't on my 350f, but was on a cb100, I know, i know......single cylinder. But runs (imo) ok.

574hondarider · « **Reply #152 on:** April 05, 2020, 05:46:08 PM »

Tore it down tonight, but didn't see anything unusual, besides piston 3 rings were close to lining the gaps up (but all headers looked pretty sooty).

Thoughts moving forward, have the cylinders spec'd for egg shape and if they happen to be perfectly round and well within spec, should I keep the CI pistons (which I hear are decent) and source some NOS Honda rings and throw it all back together? Or do I bore .25 over just for good measure? NOS rings are really hard to find!

This really puts a damper on the build....

Thanks,

jakec · « **Reply #153 on:** April 05, 2020, 09:46:08 PM »

Quote from: 574hondarider on March 27, 2020, 09:35:40 AM

If I do a .25 over, can I use a standard head gasket, and will it require rejetting (I just purchased and installed all new keihin stock jets lol)?

These are both good questions and I'm curious for the answers as well as I just did 0.50 over on my 400. No one has mentioned either to me. I ordered the piston an ring set from cruzin image and I feel like if I needed a different head gasket they would have provided it?

jakec · « **Reply #154 on:** April 05, 2020, 10:16:24 PM »

Thought about it some more and the bore (at least for the 400) is 51mm. I don't think they make oversized head gaskets (especially in only 1/4 or 1/2mm sizes) until you get up to a big bore like 454 and 466 kit.

Mark1976 · « **Reply #155 on:** April 06, 2020, 07:08:11 AM »

As has been mentioned, CI rings have dubious reputation at best and I can only go with the info supplied to this point. A compression check as is a leak down test a great indicator of where to look, your compression numbers are really low regardless. So its a good bet that the CI rings could be (are) your culprit. Now, having said that take the cylinders and pistons and get them measured, even if your going to go to an O/S pistons whom ever is doing the work has to do it any way just to be sure he (or she) knows where to start. If everything is within spec (piston to cylinder) you may just need rings, or not. As you already know any cylinder irregularities can have a profound effect, you won't know till some runs a bore gauge down them. If everything is in spec, it highly likely the rings supplied are crap. (do a search on CI rings
theres plenty of bad experiences with them) My experience has always been to do your homework then make a decision, I'll always invest my time before my money, I've made my share of poor assumptions in my day, its just part of the experience. I'm a numbers , empirical type, if that seems like too much info and for some people it can be, as has been stated earlier, you can always just go to the next O/S piston. Post some pics,
If you go next over, the std head gasket will do as will the jetting, we're talking .010 increase in bore, its not a significantly material amount.

calj737 · « **Reply #156 on:** April 06, 2020, 07:49:52 AM »

Quote from: 574hondarider on April 05, 2020, 05:46:08 PM

Thoughts moving forward, have the cylinders spec'd for egg shape and if they happen to be perfectly round and well within spec, should I keep the CI pistons (which I hear are decent) and source some NOS Honda rings and throw it all back together?

Never in my life heard of "ovating" a cylinder bore. I personally think that is most absurd bit of horsecrap I've seen on this forum. I can't imagine how a machinist would even perform such an operation??? Mills don't move in that way, honing machines don't work that way, tooling isn't shaped in that manner.

A decent hone by a qualified machine shop with a rigid hone that measures to your pistons should be all that you need with any brand of pisonts/rings. If the rings don't seal after that, get better quality parts.

574hondarider · « **Reply #157 on:** April 06, 2020, 09:05:27 AM »

Thanks for the recommendations. I've never heard of egg shaped either until Mark (hondaman) emailed me this:

"Here's what is happening, and it happens with 100% of these SOHC4 engines, in all 5 of their forms: within the first few thousand miles, the outer two cylinders warped into an egg-shape, with the blunt end facing outward at about 10 o'clock on #1 and 3 o'clock on the #4, and the 2 middle cylinder have their (lesser) blunt egg-shaped bores pointed toward the cam chain tunnel. I see it every time an engine comes to me.

This was caused by the inexpensive, uncured metals used in those days to cast bike cylinders: it actually happens to ALL of them, to a greater or lesser degree. This is why it becomes impossible to just re-ring these engines and get good results. I will not matter what rings you use: until you bore the cylinders round again, they will leak oil as the new rings cannot touch the bores in those now-worn regions.

The warp happens like this: the outer 2 (in particular) have too much more air flowing across the outer fins as it flows sideways across the face of the engine, accelerating it as it bends around the front corners. Those corners then get cooled about 20% more (in-town speeds) than the other portions of the cylinder, and that side does not expand as far away from the piston as the rest of the bore. So, all the extra pressure put on that site wears the bore. The rings were chrome top rings, harder than the steel bore.

The good news: boring it even one oversize will completely cure the problem now, AND forever, because the metals are now cured. When I took down my 750 in 1980 for rebuild at 55000 miles, it was fully 0.0008" out-of-round. I bored it 0.010" (o.25mm) and when I took it down again at 1380,000 miles (because of engine external damage from a bad storm we had here) the bores were STILL completely round. I had bought new pistons anyway (CruisinImage, no less), so I stepped up another size. It will not need another rebuild until I am dust, now."

This is a relatively new "hobby" for me so I am just trying to get recommendations from guys with more experience than myself. I'm willing to do research and spend money where needed, I don't want to overspend if not necessary, I just want to be finished with this bike lol.

BigJimG · « **Reply #158 on:** April 06, 2020, 12:40:57 PM »

I believe you're focusing in the wrong portion of Hondaman's comments.

The bore gets egg-shaped while running. Extremely hard to measure unless you know what you are looking for. By boring out to the first oversize, you get perfectly round bores that are stabilized from the engine block heat cycling, and in the future, shouldn't egg-shape again.

If it were mine, I would order the first set of oversized pistons, and have the cylinder block bored.

SOHC4 Cafe Racer Fan · « **Reply #159 on:** April 06, 2020, 06:54:06 PM »

Quote from: 574hondarider on April 06, 2020, 09:05:27 AM

Thanks for the recommendations. I've never heard of egg shaped either until Mark (hondaman) emailed me this:

"Here's what is happening, and it happens with 100% of these SOHC4 engines, in all 5 of their forms: within the first few thousand miles, the outer two cylinders warped into an egg-shape, with the blunt end facing outward at about 10 o'clock on #1 and 3 o'clock on the #4, and the 2 middle cylinder have their (lesser) blunt egg-shaped bores pointed toward the cam chain tunnel. I see it every time an engine comes to me.

This was caused by the inexpensive, uncured metals used in those days to cast bike cylinders: it actually happens to ALL of them, to a greater or lesser degree. This is why it becomes impossible to just re-ring these engines and get good results. I will not matter what rings you use: until you bore the cylinders round again, they will leak oil as the new rings cannot touch the bores in those now-worn regions.

The warp happens like this: the outer 2 (in particular) have too much more air flowing across the outer fins as it flows sideways across the face of the engine, accelerating it as it bends around the front corners. Those corners then get cooled about 20% more (in-town speeds) than the other portions of the cylinder, and that side does not expand as far away from the piston as the rest of the bore. So, all the extra pressure put on that site wears the bore. The rings were chrome top rings, harder than the steel bore.

The good news: boring it even one oversize will completely cure the problem now, AND forever, because the metals are now cured. When I took down my 750 in 1980 for rebuild at 55000 miles, it was fully 0.0008" out-of-round. I bored it 0.010" (o.25mm) and when I took it down again at 1380,000 miles (because of engine external damage from a bad storm we had here) the bores were STILL completely round. I had bought new pistons anyway (CruisinImage, no less), so I stepped up another size. It will not need another rebuild until I am dust, now."

This is a relatively new "hobby" for me so I am just trying to get recommendations from guys with more experience than myself. I'm willing to do research and spend money where needed, I don't want to overspend if not necessary, I just want to be finished with this bike lol.

I guess you learn something new every day.

I'd never heard of boring to an oval spec. I've only heard of the old Oval Piston Honda NR engines that had ovals to begin with.

574hondarider · « **Reply #160 on:** April 08, 2020, 09:15:23 AM »

Well, I took my cylinders back to the machinest and he showed me they were perfectly round and all spec'd at 47.03 at various points throughout each cylinder. So, I bit the bullet and purchased a set of nos pistons, rings, clips and wrist pins off ebay, and paid dearly for them. Hopefully this will be the last expense for the bike!

calj737 · « **Reply #161 on:** April 08, 2020, 10:47:35 AM »

Wishing you best of luck- Hopefully you'll get this sorted out promptly.

jakec · « **Reply #162 on:** April 08, 2020, 11:30:19 AM »

I bet that was expensive! oof

574hondarider · « **Reply #163 on:** April 08, 2020, 11:34:36 AM »

Quote from: jakec on April 08, 2020, 11:30:19 AM

I bet that was expensive! oof

$480.00 shipped

jakec · « **Reply #164 on:** April 08, 2020, 12:22:09 PM »

Not as bad I thought, I briefly shopped for OEM oversized, now those are expensive. Must be more rare.

574hondarider · « **Reply #165 on:** April 16, 2020, 12:04:33 PM »

Hi All,

While I have the engine down, I decided to do a float height test using the clear tube method. I had put all new keihin float needles and seats in, and I believe these were 23-24mm height on the inside. Will these levels work or will it starve my baby? Not really wanting to adjust again but if I have to now is the time.

(Stock manual says 21mm)

Thanks for the input!

Carb 4 has a little bubble in the line, I should have purged that but we can guess as to where it would have been.

calj737 · « **Reply #166 on:** April 16, 2020, 01:13:39 PM »

Looks perfect. Mount 'em up.

574hondarider · « **Reply #167 on:** May 04, 2020, 07:56:58 AM »

Well, put the NOS honda std. pistons/rings/clips/pins in and have 125 miles of success so far!! All plugs are looking like the one pictured below, put some backroad and short highway miles on her. Haven't taken her up to redline yet, going 6500-7000 max for now but fingers crossed this will be the new norm!

Also, I was able to take the bike back to the widow I purchased it from this weekend (it was her late husbands bike and he bought it new in '73). You should've seen her. She called her sons and grandson and another family friend over to see it and I had to tell the story of the rebuild like 4 times....it made it totally worth it!!! The one son started to cry. It was a great weekend!!

Mark1976 · « **Reply #168 on:** May 04, 2020, 08:03:13 AM »

Way to go, congrats ...

calj737 · « **Reply #169 on:** May 04, 2020, 11:26:03 AM »

You’re an absolute top class gentleman for thinking of that widow in the way you did. A huge tip of the hat to you-

SOHC4 Cafe Racer Fan · « **Reply #170 on:** May 05, 2020, 09:25:05 AM »

Classy! Very nice!

574hondarider · « **Reply #171 on:** February 15, 2021, 09:55:09 AM »

I realize my build has been done for awhile, but wanted to show off a spare tank I have been working on. I just got it back from my painter today and am pretty happy! I was able to source an old petcock, original badges, and nos gas cap and joker gas cap latch. Waiting for the clear to cure before I start, but here is a pic of the badge just placed up in the holes. I'm debating on painting the black in the emblem or just leaving it as is since it is original....thoughts?

Oh, I have also bought another set of shocks, went with the chrome ones this time. I gave the black set to my other bike.

SOHC4 Cafe Racer Fan · « **Reply #172 on:** February 15, 2021, 03:20:20 PM »

That's a great looking tank

bek1966 · « **Reply #173 on:** February 15, 2021, 09:06:47 PM »

Beautiful paintwork on the tank, it will look fantastic on your bike!

I kind of like the emblem as it is, unless you are planning on painting the emblems on the side covers too. If you are looking for something different, you might consider painting the white lettering with the same color as the stripes. That would look pretty nice - IMO.

Fantastic 350, what a great project!

Regards,
Brad

newday777 · « **Reply #174 on:** February 16, 2021, 08:32:25 AM »

Bob
I read through your build from the start this morning. A great find and well done on your first revive and build even though you had the hiccup and had to tear the motor down again.
I do like the new tank paint better too. The original stripe style is unique to the bike and shows class that Honda put into the bikes. The tank badge looks fine stock.
And yes it's a great story on the family getting to see it again too!
I had a friend I rode with back in 1974 and 75 that had a green 350F that we'd swap bikes with while out riding, I had a new 74 CB450. I was impressed with the power the 350F had compared to the 450 twin and much smoother too and definitely a fun bike to ride the back roads and around town on. I kept that 450 a year, 9,000 miles, and sold it to buy a new 75 CB750K5 as I wanted to do more long distance riding.
Well done on your bike Bob. Enjoy it and yes, your son will enjoy it too.

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Author Topic: '73 cb350f siezed barn find! (Read 18220 times)