Author Topic: '73 cb350f siezed barn find! (Read 18480 times)

SOHC4 Cafe Racer Fan · « **Reply #125 on:** March 14, 2020, 07:55:15 PM »

Nominated for BOTM. Can someone second it?

http://forums.sohc4.net/index.php/topic,180400.0.html

574hondarider · « **Reply #126 on:** March 15, 2020, 04:22:29 PM »

Quote from: Mark1976 on March 13, 2020, 06:20:31 PM

Congrats on finishing and taking that first ride, it was really great watching this come together, these small bore bikes are plenty of fun.

Thanks!! And thank you for all your suggestions and encouragement! I love the sound these little 4's make!

574hondarider · « **Reply #127 on:** March 15, 2020, 04:24:22 PM »

Quote from: WhyNot2 on March 14, 2020, 04:24:01 AM

Bike looks great.

Especially like those pipes. Did you have any trouble installing them?

Thanks! No trouble, they installed really easily. The only thing I don't like is I cannot remove the front motor mount to adjust my aftermarket ttr400 cam chain tensioner, so I have to adjust using the standard old one. Header from cylinder 2 is in my way...

SOHC4 Cafe Racer Fan · « **Reply #128 on:** March 16, 2020, 03:35:10 PM »

Hey there, 574!

Your build has been nominated and seconded for BOTM. Please post that you "accept" the nomination in the following thread: http://forums.sohc4.net/index.php/topic,180400.0.html

574hondarider · « **Reply #129 on:** March 26, 2020, 12:50:07 PM »

Well, you may want to pull my nomination for BOTM.

The bike burns oil and smokes more than my weber does! I've got consistant compression and the engine pulls good and sounds great, but I believe oil is getting by the crusin image oil rings. I burned a 1/2 quart of oil in 40 miles!! Blueish smoke coming from the exhaust and the crank case breather. Total I have ridden her 100 miles trying to break in, with a lot of good pulls to about 7000 and engine breaking. The bike hasn't leaked 1 drop of oil anywhere, so I am bummed to have to tear it down. Current plans are to source some NOS std. size rings and put them on the CI pistons.

I would appreiate any suggestions/magic/voodoo to not have to do this.

Mark1976 · « **Reply #130 on:** March 26, 2020, 01:52:56 PM »

lets start with,
what are the compression numbers... what do the plugs look like.
Then if you do need to pull the top end, get out the note book and camera and start with checking the rings, pistons and bores. measure it all, double check everything. See what ya have first, then start making decisions. One thing at a time. a week or two later and it'll be a distant memory.

jakec · « **Reply #131 on:** March 26, 2020, 02:44:53 PM »

I just went back through the thread and I did not see you state what size of pistons you got. If you're looking for OEM rings I'm assuming you did not overbore. I would have thought that was necessary considering the pistons were seized when you got the bike.

jakec · « **Reply #132 on:** March 26, 2020, 04:16:00 PM »

I have heard directly contradicting info here, Mark suggested that I get CI kit for my 400 only a month ago.

Mark1976 · « **Reply #133 on:** March 26, 2020, 05:05:44 PM »

It is, what it is. take it apart, go from there... ya gotta start some where... look at the upside, your familiar with it.

574hondarider · « **Reply #134 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 #135 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 #136 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 #137 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 #138 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 #139 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.

574hondarider · « **Reply #140 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 #141 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 #142 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 #143 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!

jakec · « **Reply #144 on:** April 08, 2020, 11:30:19 AM »

I bet that was expensive! oof

574hondarider · « **Reply #145 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 #146 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 #147 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.

574hondarider · « **Reply #148 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 #149 on:** May 04, 2020, 08:03:13 AM »

Way to go, congrats ...

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Author Topic: '73 cb350f siezed barn find! (Read 18480 times)