Author Topic: CB350F: two failed top end rebuilds, stock bore and 393cc (Read 35745 times)

markreimer · « **Reply #150 on:** October 01, 2017, 09:34:53 PM »

Totally. It's so wild how tight the tolerances are on these bikes. By hand I figured there was no way these guides were anywhere close to done. But to find out there is basically ten times more play than the minimum spec is crazy! .0004 vs .004.

New guides are on the way. I ordered 8 guides from Yamiya, with 8 guide seals. Gaskets are on the way as well, and a pair of OEM supply and return oil seals arrived yesterday for sealing between the head and cylinder. Now I'll sit and wait about a week or so for them to arrive. If I'm really lucky, I might even get a ride in on the bike before Nov 1st, which is basically below freezing and snowy by then.

disco · « **Reply #151 on:** October 02, 2017, 02:35:10 AM »

Hi Mark,

Don't want to be a party pooper......

4/10,000 of an inch is the absolute lower limit for the intake valve only. The service limit for both valves is 118/10,000 of inch. Which is nearly 12 thou. So your measurement of 8 thou is still within the service limit if these manuals are correct. I've attached the service data which is on this sohc website under manuals etc.

I'm thinking there's a typo in there......the service limit is at least 6 or 10 times the assembly limit, depending on which valve you consider?

However, I think you're on the right track with the likely root cause being the valve guide clearance.

markreimer · « **Reply #152 on:** October 02, 2017, 06:28:15 AM »

Hmm I see what you mean. That does seem like an odd service limit...

One other thing I noticed this morning, have a look at the staggered wear marks on my #2 piston second ring. Doesn’t seem to be a pattern to the wear or line up with the gaps in the oil ring. Any idea if this is normal? Keeping in mind there is only 80 miles on it? I’m asking because someone questioned the quality of this set of rings and I don’t know if that black coating is expected to stay put or not...

Here’s how the others are wearing in

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markreimer · « **Reply #153 on:** October 06, 2017, 12:31:24 PM »

Not much new to report here other than my last remaining parts have arrived. OEM base gasket, valve cover seal, circlips, CI head gasket, Yamiya valve guides and seals. Heading to the machine shop for the guide install.

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ekpent · « **Reply #154 on:** October 06, 2017, 12:36:07 PM »

Wish someone knowledgeable would have commented on those nice ring wear pictures you took.

markreimer · « **Reply #155 on:** October 06, 2017, 01:22:19 PM »

Me too. Pretty weird. I showed it around to some friends of mine who've build a number of motors. The best guess was from dirt/debris that wasn't cleaned up well enough, due to the fact that the piston skirts have matching scratches in most places. It's possible, I had the block and pistons off three times before I got it all settled in, which would have created lots of opportunity for stuff to get stuck to the pistons and me not notice it.

markreimer · « **Reply #156 on:** October 06, 2017, 01:24:01 PM »

Oh, I just realized you were referring to the piston ring wear marks. I was looking at photos of my 750 rings before I installed them, and two years later when I had to pull the top end off for unrelated reasons. They were black when new, and polished clean the next time I saw them. I'm pretty sure these rings look this way because they simply haven't been run long enough to fully wear away that coating. At least that's my suspicion.

Kinda re-enforced by this article here, which says the coating is for scuff protection during the early stages of an engine break-in before full oiling can be provided to the rings

https://www.hastingspistonrings.com/tech-tips-faqs/maganese-phosphate-coating-on-compression-rings

markreimer · « **Reply #157 on:** October 10, 2017, 07:18:24 AM »

I dropped the head off at the machine shop this morning to have the Yamiya guides pressed in and seats cut. For a moment I thought I'd miss my chance to get this built before winter when I could only find 6 of the 8 little o-rings that go between the guide/head, but found 'em last minute.

I brought the block along too to get his opinion on the vertical scratches. He didn't think there was any reason to hone them out as they were so subtle, but offered to throw in a light pass anyway since I had brought it in. As for the cause, after inspecting the pistons and bore he believes they were the result of small bits of particulate I didn't clean, and possibly from the edge/end of the ring scratching as it broke in. He pointed out one ring in particular, which felt pretty sharp at its end, and suggested I take a fine file or emory and lightly take the edge off.

All my other gaskets have now arrived - using OEM for all the gaskets and seals again, except the 393 head basket of course. The shop is really full at the moment, but I'm hoping to have it by the weekend. If I do, I'll have it put together and fired up before Monday.

markreimer · « **Reply #158 on:** October 10, 2017, 07:20:18 AM »

Also check out this HUGE valve they had in the shop! It’s bigger than my whole engine haha. I had to ask if it was actually real, apparently it’s from some big diesel

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markreimer · « **Reply #159 on:** October 28, 2017, 12:26:37 PM »

Got my head back with the new yamiya guides and seats cut. Can’t say I’m happy with the machine shop’s job at first glance.

This was a new machinist recommended to me by a reputable builder for motorcycle work.

The head was returned with a bunch of metal shavings in it, the guides are installed but the ports weren’t cleaned before the old ones were pressed out. I haven’t had a chance to measure with a dial indicator yet but the valves don’t feel like they are tight in the guides as per my .0004” clearance instructions. That’s just based on how it feels by hand. And it seems like the seats and faces of some of the valves had a lot of material taken out of them. I didn’t think the faces needed to be touched, just seats cut.
Looking at these photos what do you think?

I’m going to clean the head thoroughly first. The exhaust valves feel good in the guides, but one or two intakes have enough play that I can feel it by hand, which measured as a lot with the old guides. Hopefully it just needs cleaning. Should have stuck with my old machinist. My 750 head came back looking brand new.

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markreimer · « **Reply #160 on:** October 28, 2017, 01:03:09 PM »

Quote from: calj737 on October 28, 2017, 12:35:32 PM

Seats have to be re-cut with new guides. Gotta be centered and perpendicular to the guide

Right, I meant the face of the valves, not the seat in the head.

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markreimer · « **Reply #161 on:** October 30, 2017, 07:35:16 PM »

So I pulled out my new head gasket for the 393 big bore and it says it’s for a 52mm bore. But the same kit has 50mm pistons and rings. I checked online and this is the gasket cruizin image sells for their 393cc kits.

Is this normal to have a head gasket slightly larger than the bore?? I don’t have my old one anymore to compare against

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jgger · « **Reply #162 on:** October 30, 2017, 08:46:42 PM »

Someone smarter than me should chime in.............but, if I remember that "extra" space is for when you torq it down that ring will squish. The only place it has to go is toward the bore. I believe that is normal.

markreimer · « **Reply #163 on:** October 30, 2017, 10:08:27 PM »

Disregard, it’s the same as the original and I don’t think it’s an issue. Torquing the head down now

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markreimer · « **Reply #164 on:** October 30, 2017, 11:22:31 PM »

That’s it for tonight. Got the cam in and now I’ll wait a day or two and re torque the studs.

It’s dropped below freezing and the roads are icy so who knows if I’ll get a chance to really ride it till spring!!

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grcamna2 · « **Reply #165 on:** October 31, 2017, 12:24:12 AM »

subscribed,you're doing good work Mark.

ekpent · « **Reply #166 on:** October 31, 2017, 05:42:53 AM »

We can't wait till spring !!

MRieck · « **Reply #167 on:** October 31, 2017, 06:14:52 AM »

I hope the machinist installed the guide orings. Those ports should have been bead blasted before removing the guides

markreimer · « **Reply #168 on:** October 31, 2017, 07:09:33 AM »

o-rings were installed, I mentioned it to him when I dropped it off, and then reminded him again when I called to see if it had been done yet.

I thought the ports should have been blasted as well. I think I found out why they weren't though. The friend who referred me to this machinist has always requested that he not blast the ports, and has done this for a few dozen heads now. His reasoning was he didn't want the glass particulate embedded in the head and risk it getting in oil passages or something, so instead it was just scraped immediately around the guide itself.

I did not request the same treatment, and assumed mine would be blasted. But I told him about the friend who referred me there, and I guess he assumed I wanted the same treatment. That's the best I can figure.

Anyway, I've got most of the top-end buttoned up now. Tonight or tomorrow I'll go re-torque the head, put the carbs on and set the valve lash and cam chain tension.

I started cleaning the oil out of my exhaust last week (there was a ton of black shiny oil pooled in my muffler, a ton!), I figure if I don't clean it, it'll smoke for who knows how long while the oil burns off and I just don't have enough time left in the riding season to go for a long ride and burn it out. The headers don't seem to have shiny spots inside, it's just a dull matte black. I might just leave that as it'll be a real pain to clean out. If it doesn't snow or rain/freeze in the next few days I should be able to ride it around my neighbourhood by the weekend and test it out!

This time I assembled the pistons in the block mostly dry. I cleaned the cylinders with brake cleaner till my rags came out clean. I cleaned the pistons and rings groove, assembled that all together and slide the pistons in from the bottom. I gave the skirts a very light coating of oil. Assembly oil on the wrist pins and con-rods. Light smearing of oil on the valve stems and seals. Everything turns over nice and smoothly by spinning the rear wheel. Things seem to be on the right track so far.

robvangulik · « **Reply #169 on:** October 31, 2017, 09:58:12 AM »

The right track indeed

I'm glad you live far far away from here, that "350" will be almost as fast as my "400" when you're finished!

markreimer · « **Reply #170 on:** October 31, 2017, 10:04:56 AM »

Hah! I'd still jump at the chance to buy a 400F engine and drop it in. I posted a wanted ad locally a few months ago, no bites. This little 393 will pull till redline in 5th...but then comes the rub... there is no 6th gear. You'd leave me behind pretty quick

robvangulik · « **Reply #171 on:** October 31, 2017, 12:11:34 PM »

A couple of teeth less on the rear sprocket will fix that, if I remember correctly red starts at 165km/103mph in 5th....

markreimer · « **Reply #172 on:** October 31, 2017, 12:20:29 PM »

That sounds about right. I dropped a tooth in the front sprocket for more 'off the line' speed, so I'm redlining in 5th at about 95mph if I remember correctly. With the big bore I can go back to the stock sprocket.

markreimer · « **Reply #173 on:** October 31, 2017, 10:33:10 PM »

Well I wrapped up the engine rebuild today. I retorqued the studs, set the valve lash and cam chain tension, and assembled the rest of the bike.

The results are kinda inconclusive.

It started up right away and idled very nicely. But once again, out came thick smoke.

Now, I was expecting this to a point as I didn’t clean out the headers at all. Remember that this bike burned 2L in 50 miles or something, and oil was pooled in the muffler at the connection to the header. I tried to wipe out the muffler with a rag and brake clean, but it was a pretty half assed job. So I knew there was old oil in there still and it would burn and smoke this time.

It was midnight and below freezing so I couldn’t go for a long ride. But I did ride for about five minutes. It pulled nicely and I had it up to 80mph or so. Performance wise it seems as expected. I think I had a bit less smoke than last time, but honestly it’s hard to tell at night. It definitely IS still smoking though.

While idling I noticed what seemed to be water (or brake clean maybe?) dripping at the connection between the headers and muffler. It didn’t have an obvious odor, wasn’t oil like last time, and I saw it boiling on the bottom of the pipe. Maybe heavy condensation or something, which would contribute to the smoke.

After the ride I looked down my muffler. There was a thin oily residue at the tip where I had cleaned, but again that doesn’t tell me if it’s old or new oil being burned out.

What was disappointing to see was that my 1/4 plugs appear to have some oil on them. This looks comparable to my preliminary plug chip last rebuild. I had my cylinders honed, so maybe these rings just need time to bed in properly.

Overall I feel pretty deflated about this whole project. If I could take it out for a 200 mile ride and then report back, I’d feel better. But as it stands I really just don’t know if this is a success or the same old crap.

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disco · « **Reply #174 on:** October 31, 2017, 11:59:25 PM »

Hopefully its just old oil burning out of the pipe. I don't know if doing 80mph, in the first 5-10 minutes of a new piston/bore is gonna do it any good though? You can't be accused of 'lugging' it I guess

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Author Topic: CB350F: two failed top end rebuilds, stock bore and 393cc (Read 35745 times)