Topic: A Wiseco 836 kit ordered by Wednesday if possible. Need feedback please.

[DoctorMuffn]

Some may remember my "Compression..." thread posted a couple weeks back showing the catastrophic failure of my .25mm over pistons where the c-clip broke in half scoring the cylinder wall of cylinder No 2. Here's a link; it's long:
http://forums.sohc4.net/index.php?topic=93700.msg1043858#msg1043858

I'm looking into this Wiseco kit on ebay:
http://cgi.ebay.com/ebaymotors/_W0QQcmdZViewItemQQ_trksidZp3984Q2em1438Q2el2649QQitemZ260779396941QQsspagenameZSTRKQ3aMEWAXQ3aIT

It seems very reasonably priced (as long as it's new). And what I'm looking to do is make for myself a reliable runner that still gets about 50mpg while chugging along at 70mph here on Cali freeways. But it shouldn't be afraid of being pegged out either. I'm not competing, but if I wanted a moped I'd have gone out and bought one.

I've searched these forums, and I'll PM a few individuals for their input. But let me lay out what I have to see what those who are in the know think about placing this kit in my motor:

I'd be running stock coils, wires (OEM, 1 1/2yrs old, less than 7k miles use so far), and plugs (NGK D8EA, about 3k miles use); stock breaker plate with points/breakers ignition (well maintained of course - meaning sanded, cleaned, and regapped by dwell measurement every 2500 miles with the oil change); and a mostly stock head as far as shape with no port work. The head however has the CycleX valvespring and valve upgrade/replacement (part numbers RS-001 and VL-100 respectively). The big, outer springs measured 44-45kg when compressed to 28mm (spec is 45.6-51.6kg) and the small, inner springs measured 24-25kg when compressed to 26mm (spec is 22.8-25.8kg). These were much more consistent than the stock springs they replaced which were also much higher/stronger than spec. And I've installed a Web Cam camshaft with a .360 lift and 270deg duration or 237intake and 234exhaust durations @ 0.050" lift (Grind #41).

I've decked the block and resurfaced the head to clean up warpage. From this I derived the cam and crank are .013" closer so I slotted the cam gear bolt holes accordingly to compensate at ~.008" on the bolt hole circumference and then advanced the cam roughly 4deg for a little more lower end grunt. This however can be returned to stock if warranted depending on where the cam gear is when I tighten its two retaining bolts.

I've been in touch with a local retailer/machinist who advised me that the Wiseco 836 65mm 10.25:1 compression kit would ultimately be lower compression than advertised, in fact lower than stock, since I have an F motor and they're designed for K motors.

Is this true?
And how would this build look reliability-wise?

Also, part of my build would be determining the proper piston to cylinder clearance which in my research on this forum I noted HondaMan stating it should be .0008"-.0012". This is new to me as I learned in blueprinting class that .001" clearance per 1.0" of bore was standard for forged pistons.

Which clearance is right for a reliable build seeking 100k+ miles service commuting to and from work in a sort of cafe racer fashion?

[HondaMan]

I've built a couple engines with similar parts, lately. A couple of things to think about:
1. The piston clearance on the forged Wisecos is more than on the cast pistons: about 0.0018"-0.0022" because of the differing materials. This means they will always sound a little "slappy" when cold, and act slightly tight when the engine is first started up warm (not hot) after it was fully warmed, then parked a while (because these pistons cool slower than the fins and liners). So, don't fire it up warm and rap it up tight: give it a minute or two for the heats to rematch first. If you don't, over time it will scuff the wide sides of the piston skirts and start damaging the rings. This has always been the hallmark of forged pistons in these engines, when not run "just so" in daily riding. (I hope this doesn't start an argument...)
2. Those Wisecos work fine in the "K" engines as 10.25:1 compression with the stock cam, unless you also add a quench band around the circumference of the chambers to match the bores: then it comes down to about 10.1:1. With the "F" engines and that stock cam, they come in at about 10.1:1 compression without quench and 10:1 with quench bands. With the #41 Webcam, it drops to about 9.7:1 because of the excessive overlap of that cam. In any case, the compression goes WAY up, because the bores are so much larger than stock while the chamber remains the same size. Even the flat-topped 836cc (65mm) "cheapie" pistons raise the compression ratio to almost 9.5:1 with the stock cams in the "K" engines (150 PSI test pressures).
3. The #41 cam noticeably drops the midrange torque. In turn, it causes the Four to act like a Kawasaki Mach III at 6500 RPM, launching it to 8500 RPM with a sudden lunge. This is even more pronounced with the Wiseco pistons due to the extra compression. Advancing the cam is a good idea to try to tame this down, else it may be a handful in heavy city traffic situations, which was what largely caused the demise of the original Blue Streak.

Overview comments: if using the cast 836cc pistons, stick with the 0.0008" to 0.0012" clearance, break it in properly and it will become 0.0015" quickly. If using the forged pistons, the harder metals heat and cool differently from the cast versions, and do not wear in so quickly, so it takes a little more space at first to let things settle in. But, the forged pistons are not 100,000 mile pistons, primarily because they are not a matched-metal system. They will wear the steel liners faster than the softer aluminum pistons will over time, where the soft ones fairly polish themselves smooth against the harder steel bores, making them last longer.

[DoctorMuffn]

Thank you so much for your response, HondaMan. I guess this leads me to my next question...
Where do I get a Wiseco 836 kit with cast pistons if that's what I need for a 100k+ mile engine?

[MRieck]

Thank you so much for your response, HondaMan. I guess this leads me to my next question...
Where do I get a Wiseco 836 kit with cast pistons if that's what I need for a 100k+ mile engine?

I won't find one. CycleX makes a cast 850 kit

[Terry in Australia]

I'm guessing you've got an F2 or F3 engine mate? If so, your mechanic is correct, using the Wiseco "K" series CB750 big bore pistons will drop your compression ratio considerably, due to the much larger combustion chambers in an F2/3 head.

Wiseco discontinued production of their F2/3 836cc kits many years ago, but I've got a feeling that either APE or Dynoman do a big bore kit specifically for your engine. I was lucky, the guy who rebuilt the F2 engine in my K2 found a NOS Wiseco 836cc kit for an F2 engine in a Honda dealers for 100 bucks in a clearance sale. Cheers, Terry. 

[HondaMan]

Keep in mind about compression numbers: if all else is equal (like not running on nitro or something), increasing compression from 9:1 to 10:1 in any given engine yields less than 3% HP increase. It is only when this is combined with wider cams, changed timing, larger inlet valves that change volumetric efficiency, etc., that it starts making a big difference, like 10%. Mostly, it makes more heat: managing that heat into power is what increases the HP rating.

The 100cc increase of the typical 836 kit adds about 8 HP if all you do is plunk in bigger pistons, just from the displacement increase. If you increase the compression by one digit, you add around 1.5 HP more. If you add a quench band, deshroud the stock valves clear into the bores, polish those valves, fix up the typical port breathing problems, improve the chamber (in the case of the "K" bikes), set up the jetting to match, improve (i.e., ensure a long-duration) spark, and a few more 'little' tricks, you can bump into the 80 HP range with the 750 pretty quickly. Adding a high-lift cam makes sense if the inlet valves are bigger, too, else just go for a little more (+5 to +10 degrees) duration to keep the midrange power up.

[Terry in Australia]

I don't disagree Mark, but my point is that using a Wiseco "K" series 836cc kit with an F2 head will drop the compression ratio due to the F2's much larger combustion chambers.

The F2 only ran 9:1 compression with much higher dome pistons than the K series engines, so it wouldn't surprise me if using the "K" series Wiseco 836cc kit dropped the F2 engine back to 8:1 compression or even less.

Not a real performance increase, and would negate any benefit from an increase in capacity, I wouldn't have thought? Still, with compression that low it'd be a good start for a turbo project, ha ha! Cheers, Terry.    

[Jerry Rxman Griffin aka MuthaF'er]

Did we determine whether doc has a F/F1 or F2/F3? Obvious differences that need to be addressed to correctly answer questions. Whats up doc?

[lucky]

Just look at the top of the 836 pistons compared to the stock pistons. It is the shape of the top of the pistons.

As far as piston to wall clearance remember the Honda is a air cooled engine, not water cooled like a car engine or water cooled motorcycle. It is not about cast or forged pistons.
Honda  Pistons are about 22% silicon to reduce expansion.  The engine cases can expand .004-.019 thousandths.

See what I mean?

[DoctorMuffn]

Here are a couple pictures of the only original piston I kept (as a souvenir in fact).

And the number on the crank case is CB750E-3111180. I'll research what this means in dates and engine specifics. Thanks to all for the incredible feedback.

[DoctorMuffn]

http://www.sohc4.net/?p=36

According to this information my engine (crankcase at least) is an F3 from late '77 to '78.

Hey, Terry, is that 8:1 figure a shot from the hip or well-founded?

And, lucky, I think I understand that what you're saying is stock Honda pistons are hypereutectic (silicon levels above 12% I believe thinking back on my blueprinting class and the field trip through CP Pistons' factory). This makes them more brittle but less expansive when heated and therefore more consistent in performance and quieter within the engine for their intended applications. They're perfect for NA applications with low risk of pinging/pre-ignition (note knock sensers, automatically/electronically adjusted timing, and liquid-cooling in modern automotive engines by both Honda and Toyota [in my experiences]). Awful for turbo motors, but now I'm generalizing.
Anyway... What are you getting at with the expansion of the case? Do you mean the cylinder block expands that much? Are these the cylinder bores expanding outwards from the pistons within at anywhere from .004"-.019"? How much do pistons expand? I get confused here...

Thanks again.

[Terry in Australia]

G'Day Doc, yeah mate, the 8:1 compression ratio estimate was a guess at best, it could well be lower.

The piston pic that you posted is an F2/3 item, so your mechanic (and me) was correct in his assumption that the Wiseco "K" series pistons would drop your compression ratio dramatically. I tried running stock F2 pistons in my F2 that I'd converted to a K6 head and cylinders, and shut the engine off real quick on it's first run because the valves were smacking into the pistons.

With that knowledge, it's obvious that the "K" series Wiseco pistons, even with their slightly higher domes, are still way lower than the stock F2 piston domes and will provide a lower than 9:1 compression ratio in an F2/3 engine like yours. As I previously mentioned, Wiseco built a special kit for the F2/3 at one stage, but it's been discontinued for some time now. Have a look at the APE and Dynoman sites (and maybe CycleX as well) as I'm sure they do kits specifically for the F2/3 now. Cheers, Terry.