Topic: K2 cam in f1 engine

[CalleF]

Is there any problems with installing a k2 camshaft in a f1 engine? Do I need to time it differently then stock or use a different cam gear?
Thanks

[PeWe]

I have a K7/K8 cam in my K2 engine. (Swedish late K2, 1975 block, head and cylinder as K6.)

I guess F1 had same cam as K7.
I just assembled it as stock with stock cam sprocket, version with plenty of holes.

Do not think it differ much.

Same engine got Cruzinimage cheap pistons, +0.50mm. K7/K8, think F1 had those too, 392 stamp on stock version.
They bump up the compression a little.

So a K2 cam in an F1 should be possible to just put in.

[HondaMan]

It will work, but you might wish to alter the carb's jetting a bit. The F1 is set to run a little leaner in the 1500-3000 RPM range, which was done by changing the slide needle from the older #27201 needle to the #271302 (or similar numbering) in the F1's carbs, which otherwise mixed the same as the older 657(n) series carbs.

This will probably show up in the new engine as a slight flat spot until about 3200-3800ish RPM in the throttle until changed, but it will run just fine if you ignore that. The big difference in the cams are: the intake valve in your new cam opens 4-5 degrees sooner than the original one: the F1 cam opens the intake at 0 degrees TDC while the K2 cam opens at about 4 degrees BTDC. Also, the exhaust in the F1 cam stays open 5-8 degrees longer after BDC to scavenge the engine a little more (for emissions reduction) and the K2 cam  closes closer to BDC.

Most of the cam changes for the F0/1 engines were done to push the powerband upward due to the lower primary gearing inside the engine and to get the DOT off Honda's back over emissions.

[willbird]

It will work, but you might wish to alter the carb's jetting a bit. The F1 is set to run a little leaner in the 1500-3000 RPM range, which was done by changing the slide needle from the older #27201 needle to the #271302 (or similar numbering) in the F1's carbs, which otherwise mixed the same as the older 657(n) series carbs.

This will probably show up in the new engine as a slight flat spot until about 3200-3800ish RPM in the throttle until changed, but it will run just fine if you ignore that. The big difference in the cams are: the intake valve in your new cam opens 4-5 degrees sooner than the original one: the F1 cam opens the intake at 0 degrees TDC while the K2 cam opens at about 4 degrees BTDC. Also, the exhaust in the F1 cam stays open 5-8 degrees longer after BDC to scavenge the engine a little more (for emissions reduction) and the K2 cam  closes closer to BDC.

Most of the cam changes for the F0/1 engines were done to push the powerband upward due to the lower primary gearing inside the engine and to get the DOT off Honda's back over emissions.

Do the F1 have bigger valves ? Sounds like the F2 heads with bigger valves can take some extra attention to avoid valve-valve interference. I have a head I bought off Ebay years ago that was supposed to be an F model head. I only recently unboxed it and I am not sure exactly what it is. need to get it cleaned up and take some pictures. My intent was to buy an F2 head and sleeve the required head stud holes to use it on a K engine.

[HondaMan]

It will work, but you might wish to alter the carb's jetting a bit. The F1 is set to run a little leaner in the 1500-3000 RPM range, which was done by changing the slide needle from the older #27201 needle to the #271302 (or similar numbering) in the F1's carbs, which otherwise mixed the same as the older 657(n) series carbs.

This will probably show up in the new engine as a slight flat spot until about 3200-3800ish RPM in the throttle until changed, but it will run just fine if you ignore that. The big difference in the cams are: the intake valve in your new cam opens 4-5 degrees sooner than the original one: the F1 cam opens the intake at 0 degrees TDC while the K2 cam opens at about 4 degrees BTDC. Also, the exhaust in the F1 cam stays open 5-8 degrees longer after BDC to scavenge the engine a little more (for emissions reduction) and the K2 cam  closes closer to BDC.

Most of the cam changes for the F0/1 engines were done to push the powerband upward due to the lower primary gearing inside the engine and to get the DOT off Honda's back over emissions.

Do the F1 have bigger valves ? Sounds like the F2 heads with bigger valves can take some extra attention to avoid valve-valve interference. I have a head I bought off Ebay years ago that was supposed to be an F model head. I only recently unboxed it and I am not sure exactly what it is. need to get it cleaned up and take some pictures. My intent was to buy an F2 head and sleeve the required head stud holes to use it on a K engine.

Well, the F2/3 heads have DIFFERENT valves that breathe more than the "K" engines. They are slightly bigger (I have some around here, will try a comparison picture) but they are flatter on the intake side and the F2/3 cam has slightly more lift, which is/was a trick way to increase breathing. But, the F2/3 valve spring retainers are a stamped-steel (spelled c-h-e-a-p-e-r) part and the retainers are slightly too small, so over time they often pull thru the top retainer and trash the engine. Ken at CycleX has come up with a perfect solution to that, though, in his uber-strong valve spring retainers expressly for this engine, worth every cent IMHO. I have used several sets and keep a spare set in case I get another F2/3 head for rebuild.

The F2/3 head also has a larger combustion chamber than the "K" engines of any type. It is so much larger that you must use domed pistons to get the compression up to at least 9:1. If you do something like an 836cc bore kit with the normal flat-top pistons and mill the head 0.010" and the cylinders likewise (which should be done in any case to stop oil leaks) then the compression comes out about 8.9:1. So, domed pistons are needed for the compression: Honda's own domed ones got it up to 9.2:1 (advertised as 9.5:1) in the stock-size bores. This quandry sometimes drives builders to switch to forged pistons to get the domed tops, but these are too short-lived for my taste in rebuilding these engines, so I don't use them.

[willbird]

It will work, but you might wish to alter the carb's jetting a bit. The F1 is set to run a little leaner in the 1500-3000 RPM range, which was done by changing the slide needle from the older #27201 needle to the #271302 (or similar numbering) in the F1's carbs, which otherwise mixed the same as the older 657(n) series carbs.

This will probably show up in the new engine as a slight flat spot until about 3200-3800ish RPM in the throttle until changed, but it will run just fine if you ignore that. The big difference in the cams are: the intake valve in your new cam opens 4-5 degrees sooner than the original one: the F1 cam opens the intake at 0 degrees TDC while the K2 cam opens at about 4 degrees BTDC. Also, the exhaust in the F1 cam stays open 5-8 degrees longer after BDC to scavenge the engine a little more (for emissions reduction) and the K2 cam  closes closer to BDC.

Most of the cam changes for the F0/1 engines were done to push the powerband upward due to the lower primary gearing inside the engine and to get the DOT off Honda's back over emissions.

Do the F1 have bigger valves ? Sounds like the F2 heads with bigger valves can take some extra attention to avoid valve-valve interference. I have a head I bought off Ebay years ago that was supposed to be an F model head. I only recently unboxed it and I am not sure exactly what it is. need to get it cleaned up and take some pictures. My intent was to buy an F2 head and sleeve the required head stud holes to use it on a K engine.

Well, the F2/3 heads have DIFFERENT valves that breathe more than the "K" engines. They are slightly bigger (I have some around here, will try a comparison picture) but they are flatter on the intake side and the F2/3 cam has slightly more lift, which is/was a trick way to increase breathing. But, the F2/3 valve spring retainers are a stamped-steel (spelled c-h-e-a-p-e-r) part and the retainers are slightly too small, so over time they often pull thru the top retainer and trash the engine. Ken at CycleX has come up with a perfect solution to that, though, in his uber-strong valve spring retainers expressly for this engine, worth every cent IMHO. I have used several sets and keep a spare set in case I get another F2/3 head for rebuild.

The F2/3 head also has a larger combustion chamber than the "K" engines of any type. It is so much larger that you must use domed pistons to get the compression up to at least 9:1. If you do something like an 836cc bore kit with the normal flat-top pistons and mill the head 0.010" and the cylinders likewise (which should be done in any case to stop oil leaks) then the compression comes out about 8.9:1. So, domed pistons are needed for the compression: Honda's own domed ones got it up to 9.2:1 (advertised as 9.5:1) in the stock-size bores. This quandry sometimes drives builders to switch to forged pistons to get the domed tops, but these are too short-lived for my taste in rebuilding these engines, so I don't use them.

Here is the head I bought years ago. It has 32mm intake valves, 28mm exhaust valves, and the intake spigots measure 29mm ID. I do not see any head stud holes that meet atmosphere in the way through the head so it is not the F type head I was TRYING to buy when I got it :-).  According to CycleX 32mm is the stock K intake valve size. I am thinking this is a later model K head. it had the little tubular oil seals stuck to it still. I'm not dismayed to have it but would still like to have the F head I was looking for to sit beside it :-).

[Tracksnblades1]

Look and see if you can find a 410 on that head.
F0 F1 K7 K8 had 392 on theirs…

The picture is of the valve duration of FO and F1  5* btdc - 35 abdc intake..

The 77f - 78f has the 5* btdc - 40 abdc intake duration..

[Jerry Rxman Griffin aka MuthaF'er]

Flip it over and post a pic of the chamber/valve areas

[HondaMan]

That appears to be a 750K4/5 type head.

[willbird]

Flip it over and post a pic of the chamber/valve areas

[CalleF]

It will work, but you might wish to alter the carb's jetting a bit. The F1 is set to run a little leaner in the 1500-3000 RPM range, which was done by changing the slide needle from the older #27201 needle to the #271302 (or similar numbering) in the F1's carbs, which otherwise mixed the same as the older 657(n) series carbs.

This will probably show up in the new engine as a slight flat spot until about 3200-3800ish RPM in the throttle until changed, but it will run just fine if you ignore that. The big difference in the cams are: the intake valve in your new cam opens 4-5 degrees sooner than the original one: the F1 cam opens the intake at 0 degrees TDC while the K2 cam opens at about 4 degrees BTDC. Also, the exhaust in the F1 cam stays open 5-8 degrees longer after BDC to scavenge the engine a little more (for emissions reduction) and the K2 cam  closes closer to BDC.

Most of the cam changes for the F0/1 engines were done to push the powerband upward due to the lower primary gearing inside the engine and to get the DOT off Honda's back over emissions.

So I might need to change the needle or is it possible to just raise it 1 notch if it runs lean in the lower rpm?
Thanks

[Tracksnblades1]

K2 cam timing specs….

[HondaMan]

It will work, but you might wish to alter the carb's jetting a bit. The F1 is set to run a little leaner in the 1500-3000 RPM range, which was done by changing the slide needle from the older #27201 needle to the #271302 (or similar numbering) in the F1's carbs, which otherwise mixed the same as the older 657(n) series carbs.

This will probably show up in the new engine as a slight flat spot until about 3200-3800ish RPM in the throttle until changed, but it will run just fine if you ignore that. The big difference in the cams are: the intake valve in your new cam opens 4-5 degrees sooner than the original one: the F1 cam opens the intake at 0 degrees TDC while the K2 cam opens at about 4 degrees BTDC. Also, the exhaust in the F1 cam stays open 5-8 degrees longer after BDC to scavenge the engine a little more (for emissions reduction) and the K2 cam  closes closer to BDC.

Most of the cam changes for the F0/1 engines were done to push the powerband upward due to the lower primary gearing inside the engine and to get the DOT off Honda's back over emissions.

So I might need to change the needle or is it possible to just raise it 1 notch if it runs lean in the lower rpm?
Thanks

Yes, either that, or increase the mainjet slightly, like by 5. If you have the typical #105 mainjet now, you can use the #107.5 (also stamped as #108) or the #110, in the Keihin numbers.

Note: If you use the Keyster jets, these numbers are #115 (in place of #107.5) or #118 (in place of #110). Avoid Keyster's needles and needle jets, if at all possible, as that makes things harder to get working again.