Topic: Frame-up cb350f restoration, hunk o' junk transformation

[Dnor72]

Mark,
Just for reference, here are some pics of my valves after unsuccessful lapping and seats before recut. They look a lot like yours, maybe worse. I don't have any pics of the recut without the valves in place. The shop I took mine to was filled with engine heads as far as the eye could see and came recommended by a local independent Triumph/BMW shop, they definitely knew their business. When they looked at my head and valves they said a recut was necessary, but my valves were likely okay and if they weren't then they would let me know so I could source some. What I'm saying is: Trust your shop. My valves got reused, thankfully.

[markreimer]

Great pics, thanks! I'll be sure to report back what the shop says. I've got a lot of confidence in them. The guy knows these old bikes well. He knew it was a cb350 head and block before I even said a word when I walked in the door 

[markreimer]

So I had a closer look at my cylinders after honing. It doesn't look like the hone went all the way through the scuff marks.

I can't feel them with my finger nail but I can't imagine these are in useable condition this way. So either keep honing till they're gone and then measure if they're still in spec, or I'm forced to go oversized pistons right?




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[markreimer]

I do have a second cylinder block I could use as well. It's rusty but perhaps would hone out well enough if it's within spec


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[grcamna2]

You might want to bring your pistons and new rings to the machinist and ask him if he could check the bores to see if it's still within 'spec' for the piston size you have.They have lot's of different types of Bore gauges to precisely measure the i.d. of the cylinders at different depths;to you or I measuring with calipers at the top or bottom of ea. cyl. it may look with-in 'spec' but those machinist dudes can really tell you. 

[markreimer]

Good idea - bring them the pistons and rings and basically say can you hone this out and keep it within spec? That sounds like a very logical first step 

I can bring the spare block at the same time as a backup option...

And last option is the cruzin image 1mm oversize pistons and rings. $100 shipped isn't bad.

[grcamna2]

Good idea - bring them the pistons and rings and basically say can you hone this out and keep it within spec? That sounds like a very logical first step 

I can bring the spare block at the same time as a backup option...

And last option is the cruzin image 1mm oversize pistons and rings. $100 shipped isn't bad.

I'm glad you have a powersports friendly machinist who can give the correct 'fit' for the piston/cyl. w/o making it oversize like 'automotive only' shops always seem to do..

[markreimer]

Yeah totally. When I took my 750 there two years ago I brought in a photocopy of Hondaman's book, my pistons and block and asked him to follow those directions haha. He had no issue doing it... that engine hauls now 

[markreimer]

Got my head back!

The shop measured for flatness and my head was bowed about 5 thousandths out, so they milled it flat again. The valve seats were cut and the whole thing cleaned up. It looks like new!



Regarding the cylinders:

I brought my pistons and the block back for measuring. Their tools are obviously better than mine and they measured it being close but not at the max piston to bore spec according to my service manual. They honed as much out as they recommended before getting too close to the wear limit, which would require an overbore.

There are still some very slight vertical lines visible in one cylinder. The shop recommended running it as-is and they do not believe the visible lines will cause any problems with rings seating, oil burning or other problems. I suppose it's not 100% perfect, but considering the alternative is new pistons, rings, and boring the block, I've literally got nothing to loose by following their suggestion other than my time. Plus this bike is being used by my wife for putting around the city, it's no race bike...

I also brought two spare 350f cylinder blocks to see if any of them would work better, but they're from older engines and have a lot of rust on the jugs. None of them were suitable alternatives, but would work for an overbore down the road.

My plan is to take their advice and build it up with the stock pistons. I anticipate getting a good amount of life out of it this way. one day when it does end up showing signs of going south, I'll buy the 1mm or even 3mm oversized piston kits,  take one of my spare blocks to the shop and get an overbore. Then it would be a simple one day rebuild task to swap out the pistons/block. No waiting on machining.




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[markreimer]

I should note, the black marks on the head surface and valve is from my greasy fingers, it's not pitting or rust 

[RAFster122s]

You may want to knock down the rust on the spare jugs and oil them up to prevent pitting from growing with heating cooling condesation cycles.
Lube them up after a bit of time knocking the rust back and once the oil has set up for about 4 days to a week lube it up again and let it dry /setup again.  Wrap it in some oily paper and seal it up in a plastic bag airtight.

[markreimer]

Hey smart suggestion. One of my spare blocks has been sitting in an outdoor garage rafter for oh... a few decades. The other came out of a complete engine which had been stored outside for oh... a few decades  So they are rough. But I'm sure I could punch it out to 393... I'll oil them up and store them in a sealed plastic bag. Thanks!

[markreimer]

Getting close now. I installed the valve guide seals and springs on the head, new o rings on the carb intake boots, exhaust gaskets and seals around the dowels.



Next was checking the ring gap. The top rings are close but not past the max gap. Second rings are close but not at the minimum gap. My manual didn't show a spec for the oil ring. So no filing was required.



I installed the rings, which is always a nerve wracking affair for me. But a ring expander tool made it much easier. All four pistons are ready now.



I'm currently doing some final gasket surface prep and making sure all my seals and gaskets are ready to go. I'll be copper coating the head gasket, so I've got the copper spray warming up by the heater.

I noticed my replacement oil orifice seals are a different shape. The existing ones have a lip on the top whereas the new ones don't. Not sure it'll matter but it makes me a bit nervous as this is the source of the infamous 350 leak...



Old:


New:


Back to scrubbing the gasket surfaces a bit more. Then pistons are going on. I may wait till later this week to drop the block on, I could use a second set of hands...






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[markreimer]

Pistons back on after giving the wrist pins and rods a nice layer of assembly lube. Gasket surfaces are clean, ring gaps are spaced at 120 degrees apart and facing away from the wrist pins. Circlips are all in, and I'm ready for final assembly.


One question. My gasket kit came with these two seals. They look like the supports for the hard oil lines that run parallel to the camshaft on top of the head, but they're about five times bigger than they should be. I'm thinking they're not meant for a 350F. Anyone recognize these?




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[markreimer]

After test fitting my head gasket I'm unsure about these seals. The originals fit the head gasket much nicer than the new ones. The originals seems pretty soft and aren't chewed up at all. What do you guys think - re use these?



And the new ones:




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[Remcod]

Find a set oem nos ones on eBay: they are for sale but make sure they have the Honda packaging or they are just aftermarket still. My rebuild leaked after 200 and after 1200 km severely after resurfacing and with nos aftermarket ones. Now rebuild with oem seals and with copper gasket, bone dry for 500km and just retorqued but winter now. Hope this does not slow down the build but it's worth it. No idea where those big seals are supposed to go.

[Remcod]

I can add to that that when I compared the two the aftermarket ones appeared shrunken by heat causing the leak.

[markreimer]

I can add to that that when I compared the two the aftermarket ones appeared shrunken by heat causing the leak.

Thanks. What is strange is that these seals came in a Honda gasket kit, and looking at the parts fiche (checked all years) it seems this is what the seal looks like too. Very odd. So the non-lip seals I have are Honda seals, yet not the same as what came in the engine...

Sorry to hear about your leak. So it leaked once, then you resurfaced the head and it leaked again? Man, bummer! I'm using a Honda head gasket and copper coat, hopefully it helps. I've read a ton of leaky top end rebuilds on the forum here, only ones I could find that held had some kind of copper or other sealant added, so I'll give it a try. It's winter now though so I'll have to wait a long time to find out


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[markreimer]

Here is the seal in question, no lip...

 http://www.cmsnl.com/honda-cb350f1-four-1974-usa_model434/gasket-orifice_12910333000/#.WGloUGnOeEd


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[markreimer]

Some poking around brought me to this thread:

http://forums.sohc4.net/index.php/topic,111517.25.html

Quite a few people with leaking top end rebuilds using a variety of gasket brands and seals. The one guy who seems to have good luck used Honda gaskets and seals - including the oil orifice seal without a lip. Sent him a PM for more info and an update two years after his rebuild. If it's been holding, I'm going to copy that approach and use the replacement seals that came in my kit.

[DH]

Pistons back on after giving the wrist pins and rods a nice layer of assembly lube. Gasket surfaces are clean, ring gaps are spaced at 120 degrees apart and facing away from the wrist pins. Circlips are all in, and I'm ready for final assembly.


One question. My gasket kit came with these two seals. They look like the supports for the hard oil lines that run parallel to the camshaft on top of the head, but they're about five times bigger than they should be. I'm thinking they're not meant for a 350F. Anyone recognize these?




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Balance tubes for 4/4 exhaust mufflers?....(guessing)

[markreimer]

Pistons back on after giving the wrist pins and rods a nice layer of assembly lube. Gasket surfaces are clean, ring gaps are spaced at 120 degrees apart and facing away from the wrist pins. Circlips are all in, and I'm ready for final assembly.


One question. My gasket kit came with these two seals. They look like the supports for the hard oil lines that run parallel to the camshaft on top of the head, but they're about five times bigger than they should be. I'm thinking they're not meant for a 350F. Anyone recognize these?




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Balance tubes for 4/4 exhaust mufflers?....(guessing)

Wow, right you are! No wonder I couldn't find a spot for them.




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[markreimer]

Top end is nearly back together now!

Last night I slide the cylinders on and torqued the head down.

I put the new base gasket on, making sure the oil return galleys were clean and clear of debris. I used a very think film of Hondabond around the high pressure oil line and the oil return lines, above and below the gasket. I've always done that on my 750 builds and it's worked well.

Slide the block on with no issues. New o ring seals on the bottom of the jugs and knock pins in place. It's nice having that taper on the bottom of the cylinders. Makes it real easy. A thin film of oil on the jugs makes it all come together nicely. No compressor needed, just my fingers and going slow.



Then comes the head gasket and orifices. I used hondabond on the seals around the orifices like the link earlier showed. I made sure nothing got in or near the actual oil passage though. Don't want to toast this build off the bat. The head gasket got three thin coats of permatex copper coat. Knock pins in place with new seals and it was time to drop the head on





The head fit without issue and I started torquing the 12 stud nut and one 10mm bolt down. I went in three stages and brought it up to max torque. I'm going to leave it for a day or two and then come check it again. I was planning on just putting the torque wrench on at final spec. Some people back the nuts off half a turn and tighten again. Any advice? That sounds like it might break the copper bond to me.

One more session in the shop and I can fire it up! Then it's on to addressing my really leaky fuel tank. The new petcock is leaking like a sieve.


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[markreimer]

Any advice as to whether I should do one bolt at a time (loosen 1/2 turn, then bring back to torque spec, move on to the next bolt) or loosen all the bolts 1/2 turn (in reverse sequence compared to instal) and then bring them all back up to spec?

[MoMo]

Any advice as to whether I should do one bolt at a time (loosen 1/2 turn, then bring back to torque spec, move on to the next bolt) or loosen all the bolts 1/2 turn (in reverse sequence compared to instal) and then bring them all back up to spec?

loosen all bolts in reverse criss-cross as Cal mentioned then retorque...Larry