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

[grcamna2]

Need some valve tips.

Last night I did the valve leak rat and had one cylinder leaking fluid. I removed and lapped all the valves. Now all 8 are leaking!!!

I'm using permatex lapping compound and a suction cup stick. I lap till it sounds smooth, lift the valve up and do it again. Maybe three times, then add a bit more compound and do it again. After I wash it all off with mineral spirits.

Am I doing something wrong? The valves and seats look really clean but obviously it's not working.

On the plus side my donor motor came apart today and I scored two new pistons


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Mark, Possibly you could finish it up w/ a fine(220+) grit lapping compound and that will polish the valves/seats a bit more,then clean(compound) everything off real good and install the springs,etc. for 'one cylinder at a time'.The springs will pull the valves down nice and tight to seal them once you have the seats shiny,then leak-test.

[markreimer]

Need some valve tips.

Last night I did the valve leak rat and had one cylinder leaking fluid. I removed and lapped all the valves. Now all 8 are leaking!!!

I'm using permatex lapping compound and a suction cup stick. I lap till it sounds smooth, lift the valve up and do it again. Maybe three times, then add a bit more compound and do it again. After I wash it all off with mineral spirits.

Am I doing something wrong? The valves and seats look really clean but obviously it's not working.

On the plus side my donor motor came apart today and I scored two new pistons


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Mark, Possibly you could finish it up w/ a fine(220+) grit lapping compound and that will polish the valves/seats a bit more,then clean(compound) everything off real good and install the springs,etc. for 'one cylinder at a time'.The springs will pull the valves down nice and tight to seal them once you have the seats shiny.

Thanks. I decided to take it to my machinist and have new seats cut. Why not, I'm already in it this far... I pick up my honed cylinder tomorrow morning and drop off the head. I was hoping to have the engine together tonight but guess that's not happening!!

Ah well, better to take it slow and get it right.

On the plus side, four shiny pistons!




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[Dnor72]

Having the seats recut is the right move. Looks like progress to me. 👍


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[grcamna2]

Do you have any close-ups of the valves showing the seats Mark ?

[markreimer]

Hmm here's what I have




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[markreimer]

These aren't great photos though as there is a bit of lapping grit still on there, hadn't wiped them off with mineral spirits yet.


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[grcamna2]

Mark,You've got the correct idea to have the seats cut,they are rust pitted.

[Dnor72]

I see pitting in those valve seats.


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[markreimer]

Do you mean on the face of the valves themself? I agree. I think getting a proper valve job is the only thing to do now. Once I get my motor back in shape I can start thinking of some cosmetic updates so it doesn't look so brutally homely compared to your 350 

[grcamna2]

Do you mean on the face of the valves themself? I agree. I think getting a proper valve job is the only thing to do now. Once I get my motor back in shape I can start thinking of some cosmetic updates so it doesn't look so brutally homely compared to your 350 

Mark,
A good powersports machinist will tell you to replace the valves and grind the 'in-head' seats;when they manufacture the valves they are hard-faced and i've experienced that when the valves have lot's of rust pitting they need to be ground way past the hard-facing that the factory made them with and into the softer part of the valves and then the valves wear-out much quicker.The valve 'seats' in the head,well they're hard all the way through.
I'm just saying if it was my engine I would replace all the valves and have the 'seats' in the head cut for the sake of longevity.

[markreimer]

Thanks for the advice. My machinist is great, he did my 750 guides and cut new seats, a bunch of cylinder boring, and actually has done the head work on all my friends bikes too. He's taking a look at the valves to see if they can be reused. I should find out end of day, or tomorrow. If I wasn't on such a tight budget I'd just replace the valves like you said, but I've gotta make do with what I've got for now 

I picked up the cylinder this morning and it looks great, so now it's time to measure the ring gap. I have Honda rings so I'm hoping I won't need to fit them if I'm lucky, only one way to find out..

[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!

[calj737]

When you overbore by that much, larger intake vales are pretty useful to feed the new beast.

[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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