Topic: CB350F: two failed top end rebuilds, stock bore and 393cc

[markreimer]

So this is what I'd need? It says it's a Honda NOS exhaust guide for the 350F and the 400F, and appears to have a lip for a seal:


http://www.ebay.ca/itm/NOS-New-Honda-CB350-CB400-Exhaust-Valve-Guide-12203-333-335/131757834266?_trkparms=aid%3D222007%26algo%3DSIM.MBE%26ao%3D2%26asc%3D20170831090034%26meid%3D9166fe886e534601816006ad767d0fe3%26pid%3D100005%26rk%3D2%26rkt%3D6%26sd%3D120496656850&_trksid=p2047675.c100005.m1851


There seem to be quite a few part numbers for exhaust seals over the years, some with a seal and some that won't take it. pretty confusing.

Were the valve stem diameters the same for intake and exhaust?

[markreimer]

Or better yet - am I understanding correctly that the 350F and 400F used the same guides? Yamiha has a set of 8 guides, with the exhaust guides machined to accept seals:

http://www.yamiya750.com/index.php?main_page=product_info&cPath=179_273_180_186&products_id=3630

About $75 bucks CAD for 8 guides, and I already have the seals and little o-rings that go under them. Can anyone confirm my statement that the 400F guides are the same as the 350F?

[FuZZie]

http://www.ttr400.com/images/rsc05.jpg

I really need a droolz smiley.....

[bryanj]

If you email Kevin (I think) at TTR400 he has been modding these and racing them for quite a while so will be able to put you right on what can and cannot be done, and how

[MRieck]

http://www.ttr400.com/images/rsc05.jpg

I really need a droolz smiley.....

Some info that is important regarding Kevin's guides. The bore is very undersize....the guides should be reamed before installing them and then honed for final fit. The Kibblewhite 500/550 guides will work after cutting it down. Those just need to be honed after installation.
 Also....use the red viton guide seals from Kibblewhite....they are superior to the OEM pieces. I have plenty on hand if you want to purchase them.

[markreimer]

Thanks for these suggestions!

MRieck - so the 500/550 guides have the same inner/outer diameter, they just protrude into the ports further? When you cut them down, to you machine the ends to have a similar taper on the tip, rathe then just chop 'em flat? I'm guessing there are some 'flow' considerations to be make with the shape of the guide there. I'm the furthest from an expert on that topic, so talk to me like I'm clueless... because I am  Oh and would you mind explaining why guides need to be honed and not reamed? Just curious!

It seems like using 400F guides would be the easiest since TTR400 and Yamiha both make a set that are the right length and take exhaust seals. If the TTR400 guides require some extra work to fit, it seems simplest to go with Yamiha guides. Yamiha has a good reputation as far as I've heard, never heard specific reviews on their guides though.

Some of you 400F folks might also know of Rick Denoon, a fairly well known 400F tuner. Turns out he lives in the same city as I do, and I was able to ask him a few questions about this. He made a simple observation that I hope is not true, but does make sense: "If the bike is burning way more oil than before, and the only real change is the bore job, then that would be the likely place to look in my book. Just because they told you there was .0008" clearance doesn't mean that's the actual case."


Wanna place bets?

[markreimer]

Had some time in front of the computer today, and found four different threads of people who did the Cruzin Image 393 kit and ended up with major oil consumption and smoking 

CI has a great reputation around here for the 466 and 836 kits. I hope the 393 isn't a dud... sadly every single one of those threads never came to a final resolution. They just petered off after they couldn't figure it out.

Worse comes to worse, I could bore it out 1mm more and fit 400F stock pistons in there, with a custom head gasket. Blarg.



http://forums.sohc4.net/index.php/topic,161401.0.html

http://forums.sohc4.net/index.php?topic=144685.0

http://forums.sohc4.net/index.php/topic,151579.msg1731596.html#msg1731596

http://www.dotheton.com/forum/index.php?topic=63645.0

[ekpent]

 Hmmm- sure sounds like more then just a coincidence. Member Jag was signed on earlier today,toss him a PM to see what he has to say about his situation.

[markreimer]

Sent the authors of each thread a PM, waiting for a response...

If everything ends up measuring in spec on Thursday - piston to bore, ring gaps, valve clearance etc - and the rings are all in right side up, it's going to seem quite likely that the rings themselves are garbage. I'm jumping ahead of myself here, but if they are bad, what options do I have... So far I've figured:

- bore it out to 51mm and use stock 400F pistons. This will require a custom head gasket I think, as the 400F oil supply is in a different location or something. Cometic should be able to help here.

- Find another set of 50mm rings that could work with these pistons. I know some other Honda's had a 50mm bore, but I'd have to check the ring specs against this kit.

- Get custom rings made for these pistons. I sent Total Seal a message to inquire if they'd offer this service, but they don't go that small. I think JE also does custom rings. That's probably a cost-prohibitive option though.

- Find a set of OEM 3rd or 4th over pistons and rings, and hope one of my two spare cylinders aren't so badly rusted that I can't use them with a small overbore. These pistons seem to be 'unobtanium' though, or wildly expensive.

- Start looking for a used 400F engine and plop it in

[FuZZie]

http://www.ttr400.com/images/rsc05.jpg

I really need a droolz smiley.....

Some info that is important regarding Kevin's guides. The bore is very undersize....the guides should be reamed before installing them and then honed for final fit. The Kibblewhite 500/550 guides will work after cutting it down. Those just need to be honed after installation.
 Also....use the red viton guide seals from Kibblewhite....they are superior to the OEM pieces. I have plenty on hand if you want to purchase them.

If I ever get to pull the trigger on a couple of goodies from that page I'm shipping to you anyway! LOL

[disco]

Sent the authors of each thread a PM, waiting for a response...

If everything ends up measuring in spec on Thursday - piston to bore, ring gaps, valve clearance etc - and the rings are all in right side up, it's going to seem quite likely that the rings themselves are garbage. I'm jumping ahead of myself here, but if they are bad, what options do I have...

If the pistons/barrels/rings etc all come up within specification, then like Innovative said start looking at valve guides/valves. I wouldn't blame the piston kit quality just yet.

I'm a 750 guy & not entirely familiar with the 350, but have you checked crankcase/valve cover breathers are all open & clear to atmosphere?

[markreimer]

Hi Disco - agreed, I'll measure everything first. It was just a troubling discovery when I found so many others with this issue. Doesn't sit well.

I know the valve cover breather is open and free. Good suggestions. I don't think there is a second breather tube anywhere on the engine case. There is a vent tube leaving the air plenum between the air filter and the carbs, which just runs down to atmosphere.

[MRieck]

Thanks for these suggestions!

MRieck - so the 500/550 guides have the same inner/outer diameter, they just protrude into the ports further? When you cut them down, to you machine the ends to have a similar taper on the tip, rathe then just chop 'em flat? I'm guessing there are some 'flow' considerations to be make with the shape of the guide there. I'm the furthest from an expert on that topic, so talk to me like I'm clueless... because I am  Oh and would you mind explaining why guides need to be honed and not reamed? Just curious!

Same ID and OD. Honing is preferable because you can achieve a nice, oil retentive finish and get the bore exactly what you want it to be (using a Serdi pilot as a gauge). I have seen reamed guides with sloppy fit and spiral cutting marks down the entire bore.
 Yes...I cut a taper on the end of the cut.

[markreimer]

Cool, thanks!

Tonight the engine comes apart and we'll see if something obvious pops up.

Question about measuring valve guide clearance.

In the past I've used a dial indicator, lifted the valve about 1/4" or a bit more from the seat, measured the total "wobble" back and forth, then divided that number by two, and compare that figure to what is listed in the manual. For example, a few years back my cb750 had 0.005" measurable wobble, so when divided by two, it was 0.0025". The max acceptable clearance was listed as 0.003". I called it good and have been riding happy since.

My understanding is dividing it by two determines how much clearance is given on both sides of the valve stem. I based that on some reading here and some engine building tutorial stuff on youtube. Is that correct?

Here's the video I'm referencing - first the clearance is measured with a micrometer of some kind, and then using the wobble method after:

But then I was thinking, the way the manual lists piston-to-bore clearance isn't like that. It just gives a number, like 0.0004-0.0008 for the 350F. That is the difference between the width of the piston and the width of the bore, so the actual clearance around the entire piston would be half that number. It's not like a machinist is going to take that number and double it so I have 0.0004" clearance all the way around the piston, right?

If that's the case, should the number I'm looking for with the valve guide clearance be half what is listed in the manual?

My manual says Valve-to-valve guide clearance:

Intake: 0.0004-0.0012", service limit 0.0118"
Exhaust: 0.0012-0.0020, service limit 0.0118"

[innovativems]

I really have a hard time thinking it's the big bore if it smokes each time the top end was apart. 


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[markreimer]

I hope you are right. But yet it smokes, and smokes for a few others who've also replaced valves and valve guides while using this kit 

I'm not sure it makes sense to say that because it smoked after each time the engine was opened, it must be the head. Reason I say that is each time it was rebuilt, it had a different piston/ring configuration. There is a very real chance it was me who screwed it up each time, or perhaps I screwed it up the first time, and the second time was a bad ring kit.

Just as a reminder, when I bought the bike it didn't smoke horribly, but was enough to warrant a rebuild. Nobody wanted to ride behind me, put it that way. I found #1 and #2 pistons badly scarred and their cylinder walls scratched up. The bike had been crashed and dumped on the left side by the PO 40 years back, then sat. I'm wondering if it was oil starved for a few moments as a result. That or maybe I caused it when I started it up after its long hibernation. I'm just guessing here. I figured I was getting blow-by as a result, so I re-ringed with OEM rings, honed, and piston-to-bore was measured in spec by my machine shop after the hone.

Smoking started about halfway through my first break-in ride. But it was definitely down on power right from the get-go. I couldn't really even maintain 70mph. It started smoking badly about 30 miles in. Burned around 1L of oil in the 150 mile ride. Took it apart and found the ring gaps were massive, 2-3mm on some rings, and figured i was loosing compression and getting crazy blow-by as a result of the gaps. I have no clue how that gap happened, I'm assuming user error, though I have no memory of doing something that stupid. I remember measuring the gaps, and yet there they were...

Rebuilt with 393 - this time ring gaps are absolutely within spec. You know the rest - smoked instantly from start up. Way up on power, but worse for oil consumption.



My plan tonight is to ride it till it's up to temp, then do a compression test for reference. After I'll pull the exhaust and carbs and look for signs of oil making it past the guides.And after that, I'll pull the head and measure the clearance with a dial indicator, then pull the jugs and triple check I put all the rings in right-side-up, and in the right order.


More to come...

[markreimer]

For reference, here is a video of how it was smoking before I left on the break-in ride..

[markreimer]

Regarding the wobble test:

When researching this before doing my guides on my 750 I always found the "divide by 2" procedure to not make any sense, but it sure sounds like a lot of people do it that way. I think the thought behind it is that when you measure valve wobble, the valve head will move back and forth more than if the valve was moved side to side flush with the guide, as per the illustration I've attached. Best way to measure I guess would be with a split-ball inside the guide, but I don't have one of those.

In the end, on my 750 I had new APE guides installed by my machine shop, honed to the clearance spec in Hondaman's book. I can't remember if my 0.005 measurement was before or after that happened though. I would assume before, or else my machinist screwed up!

EDIT:

And here is a guy who's done both tests - first the wobble test, with .003" on his dial indicator, and then comparing it against measuring the stem diameter and the guide bore, which showed a clearance of almost exactly half what the wiggle test showed: 0.0014"....thereby supporting the "divide by 2" method...

https://www.corvetteforum.com/forums/c6-corvette-zr1-and-z06/3168420-new-ls7-valve-guides-measured-results-inside-2.html

[markreimer]

Initial findings:

Compression test shows:

1: 144
2: 140
3: 135
4: 135

Plugs look as follows after riding around town a bit prior to the compression test:



#1 looks a bit wet and also has the highest compression. Taking the headers and carb off now to look in the ports


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[markreimer]

And my beautiful mega soiled exhaust ports 1-4. These were clean when I installed the head!







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[markreimer]

And more photos. Oil on top of all four pistons. I have some scoring on the cylinder walls, though I cannot feel them at all with my finger nail. It’s also on the piston. Perhaps I wasn’t clean enough during instal...?








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[markreimer]

Had a chance to sleep on this after racking my brain last night, and made a plan.

First is the cylinder walls. They aren't damaged, look way worse in the photos than reality. I'm going to bring it back to the shop and get it lightly honed, then clean the snot out of it, as well as the pistons and ring grooves. I really don't think those vertical lines came from the ends of the rings, but rather some grit that wasn't cleaned out. Or perhaps even a casting flash from the piston, not sure if soft aluminum could cause this? What do you think? Anyway, I'll get the jugs and pistons cleaned up. That's easy enough.

As for the head, I didn't measure the valve clearances because it was just so filthy from oil. I ended up spending the evening just cleaning it. I could feel the faintest play in the guide. I'd be pretty amazed if it was past spec. But it needs to be measured, so I'll get the shop to do that for me as well. My dial gauge mount isn't stable enough to give an accurate measurement down to 0.0004".

Speaking in general, based on how much oil was pooled on top of each piston, I'm starting to agree with Innovativems' diagnosis of a head problem. I don't see how that much oil could come past the rings. I had an engine builder come by last night to take a look and he agreed, pointing out that there is loads of oil being pumped up above the pistons in SOHC4 engines, but relatively little being flung up to the underside of the pistons. It was his opinion that it would be very hard to believe how that much oil could make it's way to the underside of the piston, and past seemingly good rings, in that amount of time without something being obviously wrong.

So up next is valve guide measurements, loooots of cleaning (gotta clean the inside of the headers somehow too before the next start-up attempt), and likely ordering new guides and 8 seals from Yamiha.

THE BABY FOUR WILL RIDE AGAIN!

[MRieck]

I wouldn't bother measuring the guides......I'd just replace them. Exhaust guides with no seals are a bad idea......a really bad idea. I have personally redone rebuilt heads that the owners had insisted on non seal valve guides. They all had the exhaust ports covered in thick, baked on oil. One head only had 500 miles on it. It took forever to bead blast the ports.

[markreimer]

Thanks MRieck. I'll place an order for Yamiya's guides, which have seals all 'round.

Based on all the heads you've worked on, do you think it's possible that the guides are responsible for the oil pooled on my pistons? Intake ports looked clean. I'm just trying to avoid assuming it's the guides, replacing them, and having the whole thing happen a third time. As much fun as working on bikes is, it's kinda getting old doing the same thing over and over haha! 

[Jerry Rxman Griffin aka MuthaF'er]

Why bother to clean the inside of the header? Some will burn off and the rest is rust proofing.