Topic: which head is on my 750 F2?? Big bore question...

[koendd]

Depends on your budget...............Frank's suggestion is workable if you are careful and consistent.  Acquiring and then rebuilding a 410 head can be difficult and expensive

To improve the valve-reliefs................remove the pistons and measure the dome thickness to be sure there is sufficient metal remaining after milling to the desired depth. Assume gentle 'kissing' at this point............I would think you would want 20-thou or more of clearance...about 0.5mm.

If your cam is an F2 unit, you may be able to gain a good portion of the needed clearance with a stock K cam and only minor valve pocket machining.  The difficult part of the valve-relief machining is expanding the perimeter of the relief in direct proportion to how the valve will 'fit' into the piston with ample clearance at the radial edge of the pocket.

I had been thinking what would be the advantage of using the K head on my F engine...
Cause I would probably have to be rebuilding part of this head as well and find a new cam + holders since they are garbage now...

I found a complete F2 head (minus one camholder thing, the half moon with the 2 bolts in it) for 90 bucks 20minutes from where I live...





and here is the part where I lost you (not that experienced with engine or engine specific english ) :

minor valve pocket machining.  The difficult part of the valve-relief machining is expanding the perimeter of the relief in direct proportion to how the valve will 'fit' into the piston with ample clearance at the radial edge of the pocket.

don't get me wrong, I'm not being a pr*ck here.
Just want to make the right decision. using a K head where I have to buy a new cam and holders + milling on the pistons + the valves need lapping, skimming the head + cilinders?

or overhaul a (cheap) F2 head + skimming etc..

Money is not really a big issue since I wild spread this over the next few months, it's winter here anyways so no riding anyways and plenty of other projects ahead where I can make some money.

not that I'm a big spender but want to do it right the first time

[Jerry Rxman Griffin aka MuthaF'er]

Sounds like a standard K head. It has the 300 on it. It has 32/28mm valves. Retainers are stock looking.

The 'R3' doesn't mean anything other than a casting number. Has nothing to do with the actual grind. Sounds stock too.

Have you mentioned the piston diameter? 61mm is stock. Do they have 'HONDA' on the sides? 300 or 392 or something else on the sides? 

My thinking is your easiest way out is to find some stock 300 pistons or 392 pistons and go with what you have. You may want to consider putting a little more cam in it while it's apart.

The F bottom end (F,F1,F2,F3) only has the advantage in transmission gearing, can't remember specifics.

The F2 head you found for cheap may also need the infamous rebuild due to it's valve guide wear characteristics. Then if you have 300 cylinders with more oil returns you'd be looking for F2/F3 cylinders for the easy way out of that issue.

The only other thing I'd be curious about os which cylinders are on it. Do the oil returns match bewteen the head and cylinders? The 410 head has less oil returns.

[Old Scrambler]

If you use the F2 head.............maybe the lowest cost and will get you a 'stock' motor.  Your a very lucky person to get that head so CHEAP   If all else looks good, do a valve-seat grind, lap the valves and get the rest of tower parts............K & F towers are the same. With a good manual in hand............you can sort the o-rings and gasket requirements.  New valve guides and seals should be available from Cycle-X, or Mike Reick from this board.

[koendd]

Sounds like a standard K head. It has the 300 on it. It has 32/28mm valves. Retainers are stock looking.

The 'R3' doesn't mean anything other than a casting number. Has nothing to do with the actual grind. Sounds stock too.

Have you mentioned the piston diameter? 61mm is stock. Do they have 'HONDA' on the sides? 300 or 392 or something else on the sides? 

My thinking is your easiest way out is to find some stock 300 pistons or 392 pistons and go with what you have. You may want to consider putting a little more cam in it while it's apart.

The F bottom end (F,F1,F2,F3) only has the advantage in transmission gearing, can't remember specifics.

The F2 head you found for cheap may also need the infamous rebuild due to it's valve guide wear characteristics. Then if you have 300 cylinders with more oil returns you'd be looking for F2/F3 cylinders for the easy way out of that issue.

The only other thing I'd be curious about os which cylinders are on it. Do the oil returns match bewteen the head and cylinders? The 410 head has less oil returns.

they are 61mm indeed, haven't taken the cilinders of yet so no idea about the markings on the pistons....
Will check the oil returns tonight,

so it's still possible that I have K cilinders with F pistons?
damn, what a puzzle...

[Davidov]

Your pistons have a dome top, which is most likely F2. The piston will have "410 Honda" on the sides.

[koendd]

took the cilinders of today..
Definitely F2 piston, 410 honda as you guys said.

But about cilinders, are those K or F?
Tried checking for oil return but to be honest don't know what I'm searching for...

cilinders look real good by the way, minor scratching visible but can't feel them so light honing should do
so some new pics:







so could you help looking for me plz

one of the other options I have been considering:

keep the K head, keep the cilinders but install a flat piston big bore kit (the ebay one 836cc I think) and look for a new (or good used) cam and lifters to use on the K head I allready hav.
Might be more reliable and stronger then a rebuild F2 head that will soon or later be eating away the valves guides probably...

[koendd]

took the sump of as well.
Some small pieces of metal/aluminum but nothing to concerning I think? most of it was some sort of fiber/dirt or pieces of gasket

[Old Scrambler]

You may consider this.............put new guides and seals in the F2 head and run it with the K-cam using the K (slightly lighter) springs. That would give you the improved valve and intake-manifold sizes for good mid-range with an 18-tooth C-S sprocket. Just remember to lower the red-line by 500-rpms. 

[koendd]

You may consider this.............put new guides and seals in the F2 head and run it with the K-cam using the K (slightly lighter) springs. That would give you the improved valve and intake-manifold sizes for good mid-range with an 18-tooth C-S sprocket. Just remember to lower the red-line by 500-rpms.

haha, some more options, just what I needed 

would that be good with the 836cc kit as well?
To bad my K cam is shot, shouldn't be to hard to find a better though...

[Old Scrambler]

Yes..........but you have to get the F2 836 piston-kit to keep the compression about the same. Whether you go K or F2..........I would clean up the intake ports. By keeping the everything in the F2-3 category you will have matching oil journals.  You have F-2 cylinders

[koendd]

Yes..........but you have to get the F2 836 piston-kit to keep the compression about the same. Whether you go K or F2..........I would clean up the intake ports. By keeping the everything in the F2-3 category you will have matching oil journals.  You have F-2 cylinders

damn If they would have been K, choise would have been easy...

Guess I'll go with the F2 head rebuild then since the only good K thing I have left is the cilinder head, cam and lifters are shot so would have to find a complete head again...

[Davidov]

Concerning the metal shavings in your oil sump; most of it looks like the aluminum from the camshaft holders.

The fiber material you mentioned is most likely from the clutch plates.

[koendd]

Concerning the metal shavings in your oil sump; most of it looks like the aluminum from the camshaft holders.

The fiber material you mentioned is most likely from the clutch plates.

thx!

checked the camshaft again today and found a raised area indeed, but hard to tell whats there, first letter is like mixed S or G, second definatly a G.

Which cam is that?

and probably know what I'm going to do:

Use the F2 cilinders but connect the oil returns so I have 8 instead of 4. which would solve the oil problems with the K head on F cilinders
Buy the ebay 836cc bore kit (flat pistons)

use the K head I allready have and source a new cam and holders.

that should give an F2 bottom (which I read about are the "best") and a reliable K head with a big bore cilinder.

maybe buy a new webcam cam? which would u guys advise for "normal" street use with stock valves/springs?

does that make any sense?
Cost effective probably the easiest and cheapest choice right?

[Old Scrambler]

Take a close look at the oil-returns on the bottom of the F2 cylinder and on the crankcase................ONLY 2

By the seat or arm-pull method, an F2 cam is very similar to a K0-K1 or Web 41..............the Web 41a is more aggressive at top end (7000-rpm+)............and the basic Cycle-X cam is just slightly more aggressive than the 41a.

The more aggressive cams have slightly less everyday smoothness and torque at 4000 rpms in a K motor.

The beehive-style of valve springs offers lower seat pressure and is easier on the cam journals and rockers.........but requires new retainers.........and remember; the collets on the k-valves are different from those used on the F2-3 & K-8 valves.

BTW........that little horizontal bar indicates you have an F2 cam in the K head.

[koendd]

Take a close look at the oil-returns on the bottom of the F2 cylinder and on the crankcase................ONLY 2

By the seat or arm-pull method, an F2 cam is very similar to a K0-K1 or Web 41..............the Web 41a is more aggressive at top end (7000-rpm+)............and the basic Cycle-X cam is just slightly more aggressive than the 41a.

The more aggressive cams have slightly less everyday smoothness and torque at 4000 rpms in a K motor.

The beehive-style of valve springs offers lower seat pressure and is easier on the cam journals and rockers.........but requires new retainers.........and remember; the collets on the k-valves are different from those used on the F2-3 & K-8 valves.

BTW........that little horizontal bar indicates you have an F2 cam in the K head.

yeah my bad, I meant the cylinders have 4, crankcase leeds them to two holes...

good to know about the cam and valves!

thx a bunch!!

So the fact that my cam has worn out the holders (and itself...) could have multiple reasons? Fact oil couldn't get there and that the oil-returns weren't fully adapted?

 

[Jerry Rxman Griffin aka MuthaF'er]

Returns should have no bearing (pun) on the feed from the pump. It's likely to be the pressure itself or the orifices below the cam towers being plugged. 

[koendd]

so, in the meantime found a good F2 head with cam etc.
Will be rebuilding that one.

While I'm at it will bore the cilinders to 836cc.

Found this on ebay:
http://www.ebay.de/itm/131255080464?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

would these fit my F2? Can't really see the shape of the top of the pistons...
Friend of mine lives in Australia and comes back to belgium every once and a while so would be ideal...

[Old Scrambler]

http://www.dynoman.net/engine/pistons/custom.html#F2

Be sure of compression............one size does NOT fit all...............'75-'76............'77-'78

You missed a shipping opportunity.........I am flying to Ireland on Christmas Day.

Also take a look at what Cycle-X has to offer.

[koendd]

hey,

yeah, I've seen those but those are almost triple in price.

Plus I can get them here almost for free if my friend takes them back home.
Saves me loads in shipping and no taxes..

I've contacted the seller to be sure they would fit my model bike... but no answer yet..