Topic: Web Cam #41 in a hi-comp 849cc, advantages?

[banzaibob]

I think that I am going to put #40 pilot jets back in and sort of start over with the carbs.  (BTW, all of the combustion chambers look sooty and rich)  I am probably going to keep the main jets where they are also at #122.  Also, am I wrong in the assuming that installing the .040" base gasket and lowering the compression will go a long way in reducing the primary problem of low rpm/high load spark knock?  I would then have to start asking the stupid questions which are:

1) Is installing and/or advancing 5º the F2 cam with these hi-compression Cycle X 849 pistons in any way going to mitigate the effect of lowering the compression ratio? 

2)  What do you think the possibilities are of pistons banging into valves?  What is a good way to check for actual clearance?   

[74750k4]

All this talk of the 41 Webcam richness is bumming me out. I was just about to go to assemble this pretty stock 78K engine (some porting and studs) with one of 2 brand new 41's I have sitting here. One is a CycleX CX-1, the other just a plain ol' 41. When I pulled this engine apart I had used DP's version of the Kenny Harmon D Grind cam. Talk about carbon!!!  I have spent soooo  much time cleaning everything up. What a waste it was to try to use that cam, (although DP's ad claimed fine for street). My compression was so freakin' low (under 100) because of overlap/duration. No low end, in fact it never would idle below 1500. I saw lots of ads for these (41's) saying how these (41's) were the mildest upgrade for a stock engine. Apparently that ain't so either!

So the suggestion is stick with the stock 78K cam? Anyone need 41's ?  I was also going to try the D Grind again on a CycleX 849 kit. I guess that's out of the question  now too? So I guess I have 3 aftermarket $hit cams.

[Wobbly]

I just put the 41 into my rebuilt 77 750K7 and have no issues.
The only place I know of where you can buy a new, original  Honda cam for the K7/K8 is CMS in the Netherlands. It's priced around $1,200.00.

http://www.cmsnl.com/honda-cb750k7-four-usa_model14395/cam-shaft_14101392000/

[74750k4]

Comforting, but why all the wet intake issues flying around here??  I still have a decent stocker I  can slide in there if these other ones are garbage.

[Nic]

I didn't have "issues" with my 41 cam like bad idle and spitback or rich dramas, while I only have stock pistons maybe that helped but I found the bike really a pain to ride around town, I've read somewhere around here that the cam comes on at around 6 1/2 grand, no so with mine, at 8K it would come on. I don't ride in that rev rang much at all, I'm more than happy to change gears at 8K and usually well before that.
As I said in my post a while back, the bike with the stock F cam advanced 8° really is a pleasure to ride now, the throttle is so responsive, something it was NOT before, oh sure,  it takes a bit longer to wind out from 6 to 8k but before that it's just happening. If I reduce the advance of the cam to just 5° I reckon it would be just about right, the only thing is it's a mornings work to do it even with the frame kit so for now I'll leave it as is.
For me the 41 cam sucks, I've had the Yoshi Daytona cam back in the day n that was beautiful both with the 812 pistons and stock but this cycle X 41 cam really made the riding experience for me quite laborious. This is the first 750, the first bike of any kind, that I've had since 79 and the whole 6 months of riding this one after bringing it back from a basket case made me feel that I was just over it, but after putting the stock cam in it's now the bike I remember. The 41 cam might work out if you want to run around at redline and above all day, I much prefer a bike that responds to light throttle work than have to rev the #$%* out of it everywhere. Sorry for the rant.

[74750k4]

No, actually I appreciate your input. It could not have been as bad as my Dynoman Performance Harmon D Grind though. No idle, Zero power until 5k, above 6 plently.
I am really leaning toward the stock cam now. Shame on these advertisers with their "streetable" ads.

[Nic]

HondaMan recommends the megacycle 125-00 but I'm blowed if I know how to order one n one bloke reckons they cost $450???
Of course if you're a millionaire you could try this http://www.yamiya750.com/index.php?main_page=product_info&cPath=139&products_id=1540

[Rookster]

I called Megacycle.  They can sell the 125-00 cam to you direct.  The cost is $396.00 but they need a customer core.  They were very helpful.  If you send them the core you can pre-pay with a check or money order and they will send you back the welded cam.  You only pay shipping on the core that you send to them, so the total is $396.00.  She said it takes about 9 days to turn the cam around once they get it.  This works for me except for finding the extra $400 to spend on it.  I don't know how this would work for someone outside the U.S.

Scott

[Nic]

I called Megacycle.  They can sell the 125-00 cam to you direct.  The cost is $396.00 but they need a customer core.  They were very helpful.  If you send them the core you can pre-pay with a check or money order and they will send you back the welded cam.  You only pay shipping on the core that you send to them, so the total is $396.00.  She said it takes about 9 days to turn the cam around once they get it.  This works for me except for finding the extra $400 to spend on it.  I don't know how this would work for someone outside the U.S.

Scott

Thanks for the info mate, I wonder if they'd accept the 41 as the core? Not that I have the dough either right now. I reckon I'd have to pay shipping both ways of course so it's looking more expensive every second, add that the our dollar goin down hill fast, $500 to $600 AUD

[PeWe]

I have to keep my Action Fours SS-1 cam then. This has the WOW from estimated 6500rpm when I had no tacho.
I thought that it should be something like WebCam 41 when the numbers are similar. The shape of the lobes must be different between the same duration and max lift.

No issues driving slow, middle or fast. Idle OK.  2 persons + plenty of luggage driving slow, queues in very hot conditions as well as poring rain, on/off boats, highways in Sweden, Germany, France, Andorra,Spain, Austria, Italy,  former Jugoslavia and steep mountain/alp roads.... with pods.....
Most of the km's with lower compression, closer to OEM when my head has the chambers opened for wider old RC 836 10.5:1 pistons replaced by Action Fours pistons that are designed for standard chambers. This made the engine less wild from low, less hot, never pinging but still same top speed. But I do not recall any problems on low rpm's anyway.

Time for a CAM thread whith very streetable cams and still have the extra power! Action Fours SS-1 is my hint then.
All old cam profiles might need to be reviewed again. There is a reason for all profiles when the numbers only cannot tell how it will behave.

Is the WebCam 41 wilder then the old RC295/DP295?

EDIT: One more reason for vandalize my CB750 frame with a frame mod kit to make it possible to change cam without taking out the engine. Just remove tank, head cover, rockers arms and a few bolts more...
It will be very interesting to try different cams, just for fun.

EDIT again:
This must be Megacycle 125-00
http://www.dimecitycycles.com/vintage-cafe-racer-caferacer-bobber-brat-chopper-custom-motorcycle-engine-cam-parts-honda-cb750-sohc-megacycle-replacement-stock-cam-cb750cam-340330.html

[Wobbly]

@Nic
I am not trying to take sides here or questioning other people’s experiences. And if I would have read the negative feedback before, I probably would not have bought the cam. I merely meant to relate my experience, which is that I don’t have any issues. You see, I finally broke down to use up boxes of NOS parts that I collected over the past 30 years. I thus replaced things that were in good condition down to the last bolt and even put new cam holders in, replaced rocker arms and shafts. The entire valve train is new. Since the old cam showed some pitting, I decided to replace it as well. The cam was the only part I didn’t have as a NOS part. The only thing that actually needed to be replaced, because they were borderline, were the pistons. So I got the next bigger size +0.25. Cam aside, everything is stock. The carbs were cleaned (ultra sonic) and received new float valves and seals—all original Honda. Aside from that, I replaced the entire clutch down to the last bolt and to include everything from the clutch cover down to the basket and every little part in between (just to give you an idea how serious I took this preservation—having all parts at hand). Finally, the primary chain and tensioner were replaced.  Every part of the ignition was replaced too, plus a gazillion other things—simply because I don’t need the bike to last me more than another 37 years. When I am dead, my kids will surely trade the bike for the latest I-Pod. No need for me to save new parts when it is such a pleasure to use them. I wish, I could fix up my body as easily.
The bike runs fine. I cannot recall if it ran better 37 years ago when I bought it new (for $ 2,000). Compared to my BMW RR, it is really hard for me to judge its performance anyhow. But I like to shift early and keep it in low rpms without issues. The brakes are atrocious, which didn’t bother me 37 years ago either (I did add a second rotor now—which doesn’t make much of a difference).
This is my experience which might differ from that of other people. I guess, regarding the cam, you get what you pay for. But the price CMS is asking for the original (plus 21% VAT), seems somewhat outlandish.
Perhaps, other models respond differently than mine-which might explain different outcomes. I am not doubting your experience. Mine is different, however--for whatever reason.
 

[MRieck]

I assume all you guys with cam problems timed the cam with an adjustable sprocket?

[74750k4]

Adjustable, adjusted, re-adjusted, re-checked, re-adjusted, etc., etc., etc., on the DynoMan Performance KHD Grind.

[MCRider]

I haven't read the full thread so maybe this was discussed. And its not a straight dollar for dollar comparison, but I'd say if it were one or the other I spend the $400+ on head work and run a stock cam. This comes from personal experience.

The bike in my avatar was an 836 with a ported head and stock K0 cam. Ran amazingly well. No spit back, flat spots, pulled like a freight train.

Cams without head work are not the way to go. I can only assume problems of all sorts. I also had a stock 736, stock cam with head work. I worked in a drag race shop and this was made from parts as a shop franken bike to shoot around town on. It was amazingly smooth, and people would not believe it was not kitted.

Fianlly at that same drag race shop, we built 2 bikes for two friends. Identical 836, RC Eng pipe. One friend wanted to put it over on his buddy and secretely paid us to put a cam in his.  To his dismay and  our consternation, the bike with the stock cam was faster and ran better.

The CB750 head hides a lot of pent up horsepower.

[74750k4]

Yes, it really seems for non-drag bikes, a stock cam might be the ticket. A bit of engineering went into it. On the dragstrip you are WOT at 6500+ always. Around town not so much.

[BPellerine]

so maybe the moral of the story is that a cam alone will not make big hp diff ,carbs and head come into play among other things.these cams mentioned have been around awhile so they cant be all that bad.the mild one seem to sell well?bill

[banzaibob]

Here's another wrinkle:  Measuring the F2 cam for journal clearance.  All surfaces look normal, no galling or weird scratches.  I use the green plasti-gage.  I torque down the 6mm nuts and bolt to roughly 6-8ft/lbs.  I guess that because of 40 years of heat cycles about half the threads start to strip and come up.  On the journals that I cannot torque down the plasti-gage barely flattens.  On the journals that do torque down it shows about .003" clearance. 

I looked at the official Honda CB750 manual from 1977 and it says that camshaft to camshaft journal clearance should be no more than .0083".  .0083"?  That's a lot isn't it?  I should be happy with .003", even .004" shouldn't I? 

Also, I have the F2 head.  There's no damage, valves all look good.  They would probably need to be looked at carefully and lapped in. 

Here's a new question:

I know that you cannot use standard 836 kit (flat) pistons with an F2 head because the shape of the combustion chamber would lower the compression considerably therefore negating any (practical) power increase.  BUT.....If I have these Cycle X849cc high compression (high dome, I guess) pistons could I use the F2 heads and therefore NOT have to use the .040 base gasket I was GOING to use to lower compression?  Hmmm?  Thoughts? 

[MCRider]

so maybe the moral of the story is that a cam alone will not make big hp diff ,carbs and head come into play among other things.these cams mentioned have been around awhile so they cant be all that bad.the mild one seem to sell well?bill

I know the 41s and similar are sold as "dropin" cams. Expect power increases with little work. Maybe so, but in my limited experience, it just doesn't work that way.

I'll be quiet now.   

[Nic]

the bike with the stock cam was faster and ran better.
The CB750 head hides a lot of pent up horsepower.

Yep, absolutely my experience, my head has only deshrouding and a little porting and chamber work. Anyway, I can't really add anything to what I said previously but the difference is huge with the stock cam.

Wobbly, no worries mate, I wasn't having a go at you, more the cam.

Just as an aside, couple of days ago I fitted up the Yamiya no number 4 into 4 exhaust, I had a straight through 4/2 before, the bike now goes better again with the added back pressure of the narrower headers and the little more restrictive baffles. I think I won't need to play with jetting now.

[MRieck]

If all you want is torque put an automatic cam in.

[74750k4]

That's beautiful paint

[MRieck]

Wha?

[HondaMan]

Here's another wrinkle:  Measuring the F2 cam for journal clearance.  All surfaces look normal, no galling or weird scratches.  I use the green plasti-gage.  I torque down the 6mm nuts and bolt to roughly 6-8ft/lbs.  I guess that because of 40 years of heat cycles about half the threads start to strip and come up.  On the journals that I cannot torque down the plasti-gage barely flattens.  On the journals that do torque down it shows about .003" clearance. 

I looked at the official Honda CB750 manual from 1977 and it says that camshaft to camshaft journal clearance should be no more than .0083".  .0083"?  That's a lot isn't it?  I should be happy with .003", even .004" shouldn't I? 

Also, I have the F2 head.  There's no damage, valves all look good.  They would probably need to be looked at carefully and lapped in. 

Here's a new question:

I know that you cannot use standard 836 kit (flat) pistons with an F2 head because the shape of the combustion chamber would lower the compression considerably therefore negating any (practical) power increase.  BUT.....If I have these Cycle X849cc high compression (high dome, I guess) pistons could I use the F2 heads and therefore NOT have to use the .040 base gasket I was GOING to use to lower compression?  Hmmm?  Thoughts? 

The .0083" max. clearance value went away with the no-oil-jet sandcast heads(!). Those were the only heads (towers) that I ever saw from Honda that had less than.005" on the inner 2 cam bearings, because the inner 2 journals on the stock cams became smaller than the outer 2. Many folks today presume that since they measure the cam and find the inner journals smaller than the outer, it is toast: I beg to differ - it's probably brand new!

I recently rebuilt my trusty K2, approaching 140k miles, with the same cam bearings (aka Rocker Towers) it had when new. The outers are at .0045" clearance with the new K4 cam installed, the inners are at .0080", which didn't change even .001" from the old cam. The old cam had lost between .018" and .026" of lobe height (intakes), so I thought I'd install a newer one this time.

The reason for low bearing wear is: the shaft itself is so stiff (and heavy!) that it doesn't flex much until the RPMs are way up there. The up-down loads across the cam are largely balanced by the 1-3-4-2 firing order of the engine, much like my old Ford 2000cc OHC 4-cylinder's engine was: at more than 300k miles the cam bearings on that one (also aluminum head) showed only a couple thou of wear. Only the front bearing wore, where the timing belt was tensioned against it (end-driven camshaft). Starting in the K3, the springs became tapered and the seat pressure dropped even more, and the cams lasted longer yet. This changed in the F2/3 engines, though.

The 836 pistons: when you install those into the F2/3 engine, mill the head .040" to .060" at the same time. At .040" it works out to 9.04:1 CR with the F2/3 cam, and 9.2:1 with the K0-K5 cam. I've done several this way, and it really helps. If you don't mill the head at all, it comes in around 8.85:1 CR with the flat-top 836cc pistons and the F2/3 cam. With a Webcam 41, this would drop close to 8.0:1 CR.

[PeWe]

Very nice discussion here as it should in a technical forum.
Guys with 41 cam and late power.... maybe the cam is timed too late (retarded? Advance the timing and get more on low
If way to rich on idle. Check the ignition if F is spot on at idle AND full advance NOT BEFORE 2500rpm. Too early full advance tighten the spring(s) in the advancer unit.
I had that problem with my CB750 plus flowing carbs (clear tube showed how too much and when floats adjusted OK)

[banzaibob]

Just so we're clear, this is the 849cc high-compression kit.  The pistons are domed.  My understanding is that in using them in a standard '69-'76 head they would be hi compression.  Using them in an F2-F3 head would mean that the compression ratio would be more akin to what is stock in the F2 models.  I guess that there is a way to determine the actual compression ratio but at this point it seems a bit moot.  The salient issue is that I would not have to pull the cylinders and install a new base gasket (PITA).  The reason I don't necessarily want to do this is that the bores look perfect!  I do not want to take a chance on Occum's razor by wearing new ring end gaps where before there were none before.  Plus, I have a friend who will let me borrow his hot-shot Wiseco ring compressors but I would have to load the engine up and take it downtown to his shop (Invitation to Murphy's law) 

I would also not have to use my old head which now requires the installation of at least 4 or 5, 6mm thread inserts.  However I do think that the valves on the F2 head may be shot.  It appears that the previous owner ran with way too much valve clearance and mushroomed the stem tips.  See: http://forums.sohc4.net/index.php?topic=134581.0 The rocker arm adjusters look hammered also.  I have plenty of those.  The valve seats on the F2 head actually look pretty decent.  (Is there a way to save those kind of valves?)  The valve guides all appear to be decent, too.  The CycleX $150 valve set for the F2 looks like a hell of a value though.  When this is all over I'm going to want a free T-shirt from them for all the money I've spent. 

Correct me if I'm wrong:

My thinking is that by using the F2 head with its bigger valves and hotter cam, I can realize all of the low end torque increase one may get from increasing overall displacement and also enjoy the higher revving, better breathing characteristics of the F2 motor.  Since the compression ratio is more street friendly, this also would solve my initial problem of spark knock under heavy load. 

However one should probably by ready for my next thread which will probably be titled, "How do I get valve clearance using these pistons/F2 head?"  I'm hoping not......