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

[FuZZie]

Your thinking better/more vacuum each redo increasing the draw on the valve seals during the intake stroke? 

[markreimer]

Yeah exactly. The seals are new, but maybe the guides are so bad it doesn't matter. I'm not sure how they could be THAT bad in only 6,000 miles, but what else could it be, you know? It's happened with three different set of pistons/rings so... 

[FuZZie]

Yea I think your right and your already getting good advice.
Been following along, just wanted to offer up some encouragement. It's a #$%*ty spot to be in. If I'm remembering correctly the heads were looked after by the PO? 

[markreimer]

Not exactly. I had the head off in the winter and took it to a machine shop to have the valve seats and faces cut. I didn't do anything with the guides at that time. The seats were cut, intake seals replaced (no exhaust seals on the '74, guides can't accomodate them), and the gasket surface was milled flat.

I remember pulling the valves out 1/4" and wiggling them by hand at that time, and I remember thinking they felt so tight that I wouldn't bother measuring them. That was obviously stupid in hindsight. Very curious to see how the guides measure up on Thursday.

[FuZZie]

Why recut v.s. lapping or do you mean you had them lapped?

[markreimer]

Cal - I am blocked by him!! I bought a carb kit from him, asked some questions when I thought the kit was missing a piece (it wasn't, I incorrectly thought it came with a piece it didn't), left positive review and he blocked me haha. I've been buying stuff from him with my wife's account now. Like walking on eggshells!

FuZZie - I tried lapping them in, but no matter how much I tried, they still failed the 'leak test'. The bike had sat outside from 1976 to 2016, so i guess the faces and seats got pitted. Had them cut and they sealed right up.

[FuZZie]

Cool, and one more reason to think the valve exhaust stems may have issues.

[bryanj]

I think the 400 had exhaust seals as well so you could always fit 400 guides but be careful who does it for you as they need to be reamed after fitting with a special sized reamer and most shops don't have one and make the hole too big putting you back where you started, the 750F2 i did did not have a lot of liquid oil hanging about but smoked incredibly, enough to leave the Isle of Man policeman at the hotel in the biggest cloud of blue smoke you ever seen and raise a cheer from the stands on mad Sunday!!

[FuZZie]

This is from another tread, might be a good idea to follow along on that one to ttr400 is pretty much the go to guy on the 400's

CB350F head on Cb400F cyl's, will not work due to oil feeds on sides do not match. you would need to use the 400F cyl, requires opening up crankcase to fit.
Also the 2 front cyl studs will have to be changed for custom studs. 350F studs will not work.

CB350F did use valve stem seals on exhaust and inlet, 400F only on inlet, but can be interchanged between models. i use seals on inlet and exhaust on my engines.

[MRieck]

Not exactly. I had the head off in the winter and took it to a machine shop to have the valve seats and faces cut. I didn't do anything with the guides at that time. The seats were cut, intake seals replaced (no exhaust seals on the '74, guides can't accomodate them), and the gasket surface was milled flat.

I remember pulling the valves out 1/4" and wiggling them by hand at that time, and I remember thinking they felt so tight that I wouldn't bother measuring them. That was obviously stupid in hindsight. Very curious to see how the guides measure up on Thursday.

That's one of your big problems....run seals on both sides. 550 guides can be modified to work in the 400. I believe I modified a set for a 350/4 a few years ago.
 You will need the new guides to be honed (not reamed) and another valve job after guide replacement. I'd replace all of them.
 Don't know the condition of the valves but in the case of an old bike it isn't the mileage....it's the age. I'm talking about corrosion, the steel valve interacting with the iron guide etc
 

[Bodi]

I've heard that guides should be honed as reaming seals the surface or something like that? I don't know how much difference that makes, I have reamed a few 400 heads (I have the Honda "factory" reamer set) with no complaints...
The 400s I've seen have had unsealed exhaust guides, typically these bikes will pop a puff of smoke after idling for a while but I haven't seen issues with riding. Did any year come with exhaust guide seals?
I think you could just use eight intake guides to have seals all round- they look identical except for the seal seat but I haven't tried, worried that there's some other difference I can't see.

[markreimer]

Thanks everyone! this is some really good advice.

I've heard that some years the 350F DID include seals on the exhaust guides, though I can't find any evidence to support that in the parts diagrams. But other members here have stated they opened up their engines and found 8 seals. I'll have to check the parts fiche again to see, but I agree that figuring out a guide with a seal is a good idea on the exhaust. 8 intake guides, with the exhaust guides honed to size sounds good. Out of curiosity, why does it need to be honed and not reamed?

MRieck - thanks for that tip, I hadn't thought of that but of course now that you say it, it seems obvious!

[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.