Topic: No clearance between intake valve and piston

[Kickstart]

So I'm doing a mock-up of my engine assembly, and I obviously did something wrong.

It appears I have no clearance at all on my intake valves. 

• I have a 75 CB750F with +1mm flattop pistons from Z1.
• I did have the cylinder and head milled 0.01" each, but the original F0 pistons were a little taller than the ones from Z1, so that shouldn't be an issue
• I'm using an adjustable cam sprocket, and I thought I had set it so it was 8 degrees advanced from stock (I assume I somehow messed this part up.)

I'm a little worried I damaged my engine.  I could the turn the engine over using the nut on the alternator... and it did give me some resistance (which I assumed was the clay being squished).... now I'm wondering if I bent something.

[Hondawggie]

Tricky problem, and I'm not an engine builder, but it seems like the weak link in the chain in the case you have would be a bent valve.  If it were mine I'd pull that valve and have a look.   Turning a motor over by had in that low-stress condition though is not like a valve/piston contact in a working motor, which can bend the valve so maybe in your low-frequency (how many times did you cycle it, I assume 1 or 2) rotation of the works under nothing approaching the explosive force in a running motor, maybe you got away with it.  If it were mine I'd inspect the piston head and see what kind of imprint if any is on the crown.  Hard to tell with the clay obscuring it.   

[andrewk]

I bet your engine parts are ok, but I agree that you will want to check the intake valve(s) that hit to be sure.

To solve the problem, though I think you will want to verify that you are degreeing the cam in properly, then once you know the cam is actually at x degrees advance, you can re-test for clearance.

[Xnavylfr]

To check for a bent valve ,You can do this,  Loosen the tappets so they are completely backed off the cam and valve (so the valves close completely) Next turn the head upside down and level. Then fill the combustion area with Transmission fluid,WD-40, or some thin(10W). If you bent a valve the oil will seep past them, OR try the FLASHLIGHT trick, Shine a BRIGHT light from the top of the head through the exhaust and intake ports and look for light around the seats of the valves.  I made the same mistake on a KZ and it don't take much to BEND a valve.

Also for info<< the F model pistons were domed and had valve reliefs in them.F Models have larger valves and were Higher compression engines.

Xnavylfr(CHUCK)

[Kickstart]

Thanks guys... I'll do some close inspection of the valves today.  It drives my crazy that I wasn't more careful with this step.

Everything looked good, but I'm assuming something had to give... I'm thinking that means something had to bend or flex. The valve might have "just" touched as piston #3 still had a extremely thin coating of clay on it.

Oh, the F0 pistons are not domed that much (unlike the F2/3 pistons).
I have a picture comparing the new Z1 piston with the my old F0 stock piston in this post:
http://forums.sohc4.net/index.php?topic=107713.msg1240702#msg1240702

[Xnavylfr]

You are correct the 75/76 F models were flat tops ,they change thing up in 77..
Did you have a HEAD gasket under the HEAD when you checked for clearances?

The gasket gives you about .030  differance.


Xnavylfr(CHUCK)

[Kickstart]

Yeah, I'm using an OEM head gasket.

OK, I'm pretty sure I messed up advancing the cam and managed to advance it close to (or over) 10 degrees. Combined with milling off a total of 0.02" between the head and deck was enough to have the intake valve touch the piston.

It doesn't look like I caused too much damage.  I did the leak test with ATF fluid and no valve leaks.  However, I can see some grooves that were pressed into the side of the intake cutouts.

Pictures attached.  you can see a small grove that was pressed into the side of each cutout.  Hopefully I didn't damage anything else.  I'm thinking I can just smooth out these groves with some wet/dry.

[Kickstart]

OK... so I did the clearance test/measurement again but this time used the stock cam sprocket to get a baseline.

With the cam sprocket, the clearances were fine (see attached pictures).  I forgot to write down my measurements of the clay, but as I recall the readings were around 2.5mm... I believe that's plenty of clearance.

Next post is going back to the adjustable sprocket...

[Kickstart]

I was a lot more anal about getting the cam advance properly this time.

I attached a picture of the cam sprocket with adjust to 8 degrees advanced cam timing.
I also attached a picture of the end of the cam at piston 1 TDC (yes I know it's upside down - I snapped the picture after rotating the crank 360).

[Kickstart]

With the cam advanced 8 degrees the intake valves don't contact the pistons.  However, it doesn't look like I have enough clearance.

As best as I can measure, my clearance is only around 1.25mm.  I got one measurement of 1.2mm but I might have squeezed the clay with my calipers on that measurement.

Pictures attached.  I think I read somewhere that you should have 0.08" clearance (about 2mm) so I'm thinking the 8 degrees advanced isn't going to work for my set-up.

I think I'll try this again at 5 degrees, and this time use a degree wheel to make sure I'm super accurate.  While I was anal about advancing the cam, I still based it on the location of the stock cam sprocket.  So I might still be off by a couple degrees.

Oh, also, all measurements were done with the valve clearances set at stock specs (0.002mm intake and 0.003mm exhaust).  Not that 1 or 2 thousandths of a mm would make a significant difference.

[MRieck]

8 degrees is an awful lot of advance.....why do you want to run that much?

[bwaller]

8 degrees is an awful lot of advance.....why do you want to run that much?

I would like to know too. Also I'm not sure how you degreed the cam without a wheel but that should be a must, get the largest diameter you can. The 1.25mm clearance is probably enough on the intake, but 8 degrees? I imagine it's a typo but recommended lash S/B 0.002" & 0.003".

[Kickstart]

Yes, typo on the valve lash... I set them to 0.002" and 0.003" I/E respectively.

I'll make a degree wheel (or buy one).  Doing this without one is probably not accurate enough. I was also thinking I might be able to use the starter clutch gear as a degree wheel... but I probably should just do it the right way.

The 8 degrees is HondaMan's suggestion: "brings the power on sooner, putting it right where you ride most often, instead of above 6500 RPM".

He originally suggested I advance it 3-5 degrees, and when I asked if that also applied to my F model (as I thought the cam timing was different), he replied as follows:

"It is different: it is 5 degrees LATER than the K models. For the same performance, you must bring it forward even more, to 5-8 degrees advance. This is why, ror instance, the old R/C Engineering cam sprockets used to have multiple holes in them: one at 0 one at 4, (some were 5) and one at 8 degrees, so you didn't have to slot them.

The F cams (and K7/8, and many later K6) were all retarded 5 degrees for emissions reasons, making them run very lean in the 3500-6000 RPM range. This is one big reason why the later valve guides wear so fast: the engines run hotter than the earlier ones, largely from this change."

I'm thinking I'm might just advance it 5 degrees to give me a better margin of safety on my inlet clearances.

I also found some other threads on Valve/Piston clearance (with posts from both you and MRieck):
http://forums.sohc4.net/index.php?topic=86358.0
http://forums.sohc4.net/index.php?topic=39029.0
I think I'll try taking the measurements they way you guys suggested.  It is kind of a pain to accurately measure the clay.

Oh... any thoughts on potential damage I may have caused?  I'm hoping I dodged a bullet and can get by with just sanding down those imprints/grooves on the piston heads.

Thanks for the help!

[scottly]

I was also thinking I might be able to use the starter clutch gear as a degree wheel...

The starter gear isn't locked to the crank, except when cranking the motor. Even then, it will engage in a different place every time. It CANNOT be used as a reference. Do yourself a favor, and simply install the cam "straight up".

[scottly]

Btw, I wouldn't worry too much about the "damage" to the pistons; the PO of my bike left much deeper marks, without bending valves or other complications.

[Kickstart]

I was also thinking I might be able to use the starter clutch gear as a degree wheel...

The starter gear isn't locked to the crank, except when cranking the motor. Even then, it will engage in a different place every time. It CANNOT be used as a reference. Do yourself a favor, and simply install the cam "straight up".

    Right, of course.  I'm an expert and coming up with bad shortcuts.
... But now you're recommending I do myself a favor?  Man that hurts. 
In spite of my own stupidity; come hell or financial ruin... I'm going to figure this out and get this baby dialed in.

Btw, I wouldn't worry too much about the "damage" to the pistons; the PO of my bike left much deeper marks, without bending valves or other complications.

Cool... thanks for sharing that!  I was pretty disgusted with myself after all the time and money I spent that I wasn't more careful.  This definitely gives me some peace of mind.

[754]

 Grind bit off the piston,looks like the notch is centered but not to the valve.

[bwaller]

I usually check valve/seat seal with a thinner fluid (ie varsol) but if you didn't see any pass I'm sure the valve is fine too. One other item I'd suggest is a positive piston stop to find true TDC. Often the advance/case mark is off a little, so with a large degree wheel and a bit of "back n forth" you'll know you're dead on TDC. Best way to start the process.

[Kickstart]

I would like to know too. Also I'm not sure how you degreed the cam without a wheel but that should be a must, get the largest diameter you can...

Yeah, I must have been inhaling too much brake cleaner fumes. 

I spent all last night doing this again with the free degree wheel template I found here in the forums.  Even with the degree wheel I was having trouble getting repeatable readings within +/- 1 degree. I'm going to find a larger degree wheel.  Anyone know how large the APE degree wheel is? I couldn't find the diameter listed on their site.

I don't have a piston stop, but since I had the head off I just used my dial indicator to fine TDC and set the degree wheel.  This seemed pretty accurate, with the only risk of jarring something on head assembly.

Using the stock set-up again (stock cam sprocket), with the degree wheel.  I measured the intake opening as being 4-4.5 degrees after TDC (0.04" lift with 0.002" lash, measured off valve retainer).  This seems wrong, as I now realized spec should be 0 degrees TDC.  I'm thinking I should have done this with no lash. Any thoughts or suggestions?

I then did this again with the adjustable sprocket.  I ended up setting the intake valve to be at 0.04" lift (again with 0.002" lash) with 3 degrees Before TDC.  (It was around midnight at this point and I was thinking that's about 7-8 degrees advanced from the stock... but now that I think more about this I should have tried setting this to 8 degrees before TDC.)  I used clay again, but this time most of the clay pieces got moved around while I was trying to dial in the cam.  I was able to get one good intake clearance measurement: 1.9mm (which seems good).

BTW, I tried to "gingerly" pry the valve down but I just couldn't get myself to do it.  It felt like I was doing bad things to the rocker assembly. 
http://forums.sohc4.net/index.php?topic=39029.0
Does anyone have a picture on how this is properly done?
I was thinking I could also just replace the valve springs with much a weaker spring (from the local hardware store)... Any thoughts on how well this would work?

I also found this post from HondaMan:
http://forums.sohc4.net/index.php?topic=115270.msg1300521#msg1300521
I'm using a new cam chain (HD) but not a new front cam slipper.  I think I'll try this again with a new slipper, and a larger degree wheel.

[bwaller]

Everyone has their method. I like to set lash at "0" and only use the inner valve spring for less resistance.

[RSchaefer]

I recently did all of the same stuff!  Got very very confused and was also kibitzing with Hondaman.  I too have a '75F and removed .01 from the head, NOT the cylinders.  I hone cylinders, no bore and cleaned and am using stock pistons.  I too was going to do the 5-8 degree advance per HM.  I made a piston stop from an old spark plug (very easy to do) and basically ran into the same problems you are having.  I was using same degree wheel you have.  I think I finally moved the dial indicator to the top of the spring holder on the valve as this would be after all the lash.  I too purchased a slotted cam chain sprocket to do the advance.

I did what I thought was 8 degrees advance and stopped the motor from turning, valve hit a piston.  SO the long and short of it was, my stock "F" was NOT 5 degrees advanced as HM had said, it was at 0 degrees.  I found this out after I finally got my measurement setup correct i.e. dial indicator and degree wheel and remounted my stock sprocket.  Also the notch on the cam was not precisely exact, very slight to one side.

So part of this effort is degree'ing, finding the exact different between 1-4 and 2-3 and splitting the difference and then in my case, advancing 5 degrees.

[MRieck]

That wheel you have looks like 7". I believe the APE wheel is 7" too. I use either a Moroso 11" or 18" wheel depending on how space i have to work with. The one you have is accurate enough. use a piece of wire i.e. clothes hanger, sharpen one end and bolt the other end to the engine cases somewhere. When you get to TDC bend the wire so it is centered on TDC on the wheel. I like to read my #'s at .040 lift though .050 is fine too. I run the indicator off the retainer so I can see what the valve is doing in real time. I also check everything at the lash I will be using.

[kybushdr]

I know this is not a reply, but i have no earthly idea how to post a question.  I've spent 4 hours fooling with all this.....so sorry about the incorrecet placement.   I am working on a honda 350f, the motorcycle jack makes contact with the pipes instead of the frame, ok to put the weight of the bike on the pipes?  Just seems wrong, even if i move the jack forward or back, doesn't really mattter the bike will be lifted  and pressure applied to the pipes to lift the bike.  thanks for any help, sure hope to have it running by spring.

all the best,

kentucky ken

[Kickstart]

I know this is not a reply, but i have no earthly idea how to post a question.  I've spent 4 hours fooling with all this.....so sorry about the incorrecet placement.   I am working on a honda 350f, the motorcycle jack makes contact with the pipes instead of the frame, ok to put the weight of the bike on the pipes?  Just seems wrong, even if i move the jack forward or back, doesn't really mattter the bike will be lifted  and pressure applied to the pipes to lift the bike.  thanks for any help, sure hope to have it running by spring.

all the best,

kentucky ken

Hi Ken, welcome to the forums.

I would not lift the bike by the pipes.  While I don't have any experience with the 350's, and they are probably a lot lighter than the 750, I suspect you could damage a pipe.

To post a question, go to the "SOHC/4 Bikes" forum topic, and in there click the "New Topic" button at the top of the page.

Good Luck!

[Kickstart]

bwaller and Mrieck... thanks for all the help!

That wheel you have looks like 7". I believe the APE wheel is 7" too. I use either a Moroso 11" or 18" wheel depending on how space i have to work with. The one you have is accurate enough. use a piece of wire i.e. clothes hanger, sharpen one end and bolt the other end to the engine cases somewhere. When you get to TDC bend the wire so it is centered on TDC on the wheel. I like to read my #'s at .040 lift though .050 is fine too. I run the indicator off the retainer so I can see what the valve is doing in real time. I also check everything at the lash I will be using.

OK, so it looks like I did it correctly then.  I'm surprised my stock set-up is so late.  I'll try it again with a new front slipper, but I'd be surprised if that makes a significant difference as my engine only had 20k miles on it.

RSchaefer -
I think I read through a couple of your threads, thanks for posting those.  HondaMan told me our F bikes (75/76) were 5 degrees later than normal (and I believe normal was 5 degrees BTDC for the earlier K bikes) - so your measurement of 0 degrees TDC sounds right.  I'm not sure why I'm getting 4 degrees after TDC... I assumed it was because I did something wrong, but now I'm thinking it's just the way it was made.

So you went with 5 degrees BTDC with the stock cam.  How do you like it?  I plan on doing a lot of touring (including some long stints on the highway) so I'm still debating how much I really want to advance it.