Topic: 836 kit options

[SOHC steve]

Hi guys,I am thinking of running a 836 kit in my K6,but have read in the archives that some have oil leaks,blow by probs.I was wondering if this was caused by the sleeves becoming too thin due to the overbore and causing rigidity probs,especially in an aircooled engine.Just thinking out loud,but,has anyone bored out a block to take modified DOHC900 sleeves or something similar? Im just thinking that by restoring the sleeve thickness back to something like a standard engine,bore rigidity would be improved with less blow byand.......more power .
    Also,with all the brands out there that do 836 kits,has anyone found one brand to be better than others? (Ive used JE stuff in cars and found it to be very good,but have never used Wiseco or Arias)
                  Thanks.....Steve

[sandcastcb750]

I think the success of the 836cc job is a matter of how good the engine builder is rather than parts, but I may be wrong. My 836cc didn't leak until it I ran it into Boston, during the day, stuck in terrible traffic and it was 95 deg F in August. Overheating could be a problem.

[Soos]

Definately might think of an oil cooler if you do overbore that big.

There isn't much left of the cylinder wall at that point.
Much bigger and you have to re-sleeve.
For 200.00 cycle-X has 85.5mm pistons for sale. on e-bay.

l8r

[SOHC steve]

Where did your leaks come from...was it the head gasket or did you mean leaking as in blow by? Overheating would be a real issue for me,fairly high temps are typical over here,maybe a thicker sleeve would help keep the heat transfer down? What brand kit did you fit by the way.

[joeb]

Alot of people get oil leaks from under the cam towers the round rubber disks leak.  Wiseco 836 kits I think are the best. 

[eurban]

The 836kitted engines can be done up as a reliable motor.  Probably no need go to the trouble and expense of installing thicker sleeves etc.  The Wiesco kits use high quality forged pistons and are probably a bit better than the less expensive cast Cycle Exchange ones but I am no expert.  The larger displacement and higher compression will certainly generate more heat and stress on the motor and of course performance people will probably work there motors harder.  An oil coiler and the setup of the motor with proper fuel and ignition is a must.  I am just now discovering that on my wieseco 836 that colder plugs and a bit less timing advance are the difference engine self destruction and smooth running.  You will also probably benefit from chromoly cylinder studs and good quality (OEM except for head gasket of course) and properly installed gaskets and seals.  These will help to minimize the chances of leaks.  I have never seen a discussion focusing on the thickness of the cylinder walls as the culprit for leaks and most seem to be either caused by the cylinder head pucks under the towers or are seeping from the valve cover etc.  The higher compression engine and the nature of the piston rings may contribute to increased blowby and crankcase pressures.  I have also heard it postulated that the profile/ shape of the backside (down side) of the Wiesco piston may generate an increase in pressure as it is works it way back down.  Some have suggested drilling  the 2 & 3 tappet covers and installing vent hoses to help releave some of the additional pressure and I may eventually give this a shot.  So far the only areas where I have had any seepage has been the valve cover and I stupidly used an aftermarket gasket there.  Good luck

[joeb]

What plug are you runnung in your motor. Thanks

[Sam Green Racing]

The 836kitted engines can be done up as a reliable motor.  Probably no need go to the trouble and expense of installing thicker sleeves etc.  The Wiesco kits use high quality forged pistons and are probably a bit better than the less expensive cast Cycle Exchange ones but I am no expert.   I have also heard it postulated that the profile/ shape of the backside (down side) of the Wiesco piston may generate an increase in pressure as it is works it way back down.  Some have suggested drilling  the 2 & 3 tappet covers and installing vent hoses to help releave some of the additional pressure and I may eventually give this a shot.  So far the only areas where I have had any seepage has been the valve cover and I stupidly used an aftermarket gasket there.  Good luck

As eurban stated, put vents on the 2 and 3 inlet tappet covers and fit a decent oil cooler.

Are you doing any other mods to your motor ?

Sam.

[SOHC steve]

Thanks for all the input.I will def go for an oil cooler(thanks soos and sam).Interesting point about the bottom of the Wiseco pistons...I wonder if the other brand pistons have a better design? It sounds to me like oil leaks are certainly more of a prob with the 836,I guess fitting extra breathers is a big help,but I was looking at hopefully reducing blow to start with and keep it all looking stock.
     836 is a fairly big increase in capacity and the crankcase area is probably fairly small,prob doesnt help much either,but,even with this overbore,its still a small diameter in comparison to other engines and surely ring sealing to the point where there is not a prob with blowing oil out past seals and gaskets should be achievable


Are you doing any other mods to your motor ?

Sam.

          As far as the motor goes,well,Im open to suggestions.I basically want a nice original looking K6 with extra power.I was thinking of;
836 kit,mild cam (open to experiences,suggestions!),porting,polish/shot peen rods,balance,pod K+N filters enclosed in original air box,possibly bigger carbs if recomended,good ignition (maybe MSD?)and hopefully stock 341pipes.I really want to keep the stock exhaust,to the point that if you guys think they would be too restrictive for the 836 I would prob cut back on the mods a bit to keep things better suited to them.
      I might see if I can get hold of an old block to play with,it wouldnt be too expensive to try the thicker sleeves (a few friends I know could prob help out there).It might be worth a try...Thanks again for all the input........Steve

[RRRToolSolutions]

Steve,

I was going to stay away from his thread when I first saw it because I didn't want to come across like "do what I did". I spent an insane amount of money on my K4, but will likely put less than 2-3 thousand miles on it in the next 20 years.

Make darn sure you add the later model, higher strength rod bolts. Find Mike Rieck and he'll tell you which ones to use because at anything hogher than stock rpm - those old rods will fail. Anyway, start with the head. Absolutely do not start a build unless you make the head a part of the plan. The stock head already won't feed 736cc's very well, let alone 836cc. Adding a cam won't fix the head's restrictions and shortcomings. You can read the Jerry Branch flowbench article that's linked on the faq thread. It's not speculation - there are flow numbers to support. Horsepower is rpm x torque / 5252, so an rpm increase must be part of the plan.

You will not be happy with an 836cc bigbore or new camshaft, I mean you will be able to feel it slightly and it's nice to tell the buddies, but neither of these is worth the expense or trouble.....unless you port! I've never been impressed with increased displacement. Yes, same weight and a littlemore uumph, but maybe 5-10% at most. Ok, on a good day with the wind at your back it will feel stronger. Add professional porting, good cam (I love my Megacycle cam), Kibble White springs, and you will be amazed! You don't even have to go bigbore to get good great results.

That plan for stock pipes is not idea. You certainly will need to do some work to improve breathing on the intake side (you're "pumping it up"), so you have to get more in and more out. Neither the stock pipes or the air filter is going to help you there. I think the header diameter will work, but the baffles in the pipes would be restrictive for a fire-breathing 736 and almost suredly an 836.

I don't buy the 836 causing oil leaks. You have 1&4 going up while 2&3 are going down. There is a constant balance of crankcase pumps (pistons coming down). My leaks came from mistakes on the sealing rubbers under the towers, being too careful about cam break-in and over-oiling the topend and laying the gasket over oil-slicked surfaces, and not sealing the small 6mm studs for the cam towers over the sparkplugs. I'm at 400 miles and I'm convinced I'll never see a leak.

I'd like to see you do a higher compression 736cc, ported, mild cammed motor with your stock pipes and airbox for starters. At least your engine will be done and the other items will bolt on/off. If you're not satisfied, you could simply add the pipes and the K&N's. Figure modern 600cc bikes make 108 horses - you don't have to have 836cc to make it perform. Porting is the absolute "bang for the buck" out there. It makes monsters out of little motors.

I should add that I am not an old hand at the CB750. The one I bought on EBay last year was my first. I've built it twice now going for more and more go-fast goodies. I do have many, many years of outboard and motorcycle engine performance building experience. These principals are applicable to all engines - 2 stroke and 4.   

Best of luck and keep us posted.

Gordon

[Jerry Rxman Griffin aka MuthaF'er]

Do any of you guys talking extra vents on tappet covers have any pictures of what you have done? How are you actually doing this and how are you routing the hose/adding filters?

Jerry

[SOHC steve]

Hey Gordon,thanks for your input...your info is very much appreciated.....other peoples experience is exactly what I am after! I probably should have been a little clearer about the pipes and "cutting back on the mods" comment I made,I  did mean capacity as well.....I really want a well mated package with the original pipes included (when you said the baffles are restrictive,did you mean the rear removable baffle or is there others inside the 341 pipes?could they be modified?),any suggestions are all good to me Steve

[RRRToolSolutions]

Steve, go read here then come back. It will clear the mind and give you a new perspective on your project -

http://members.tripod.com/cb750k2/Technical/porting/Porting_the_Honda_Head.htm


I know the ration of exhaust port area to expansion chamber volume and length, but not for the Honda. It would seem to me that you could have the flow of your stock or modified pipes measured and as long as they met or exceeded your planned head flow, you'd not hurt performance. Smaller pipes generally improve mid-range torque while large diameter headers allow unimpeded flow for higher rpms. Heat and velocity are good things when trying to evacuate the cylinder.

For example, a smallblock 350 Chevy used for street riding loves 1 5/8" headers in the 2,500 to 5,500 range. Spin one up for the dragstrip and design it to turn 6,500-8,000 rpm - you better have 1 3/4" headers. If you're going after a high rpm, ported, screaming, sleeper bike and plan to turn some serious rpm to make the horsepower, you better re-think those stock rods. Falicon or Carillos will be necessary for serious rpm increases. Ask Hondaman (Mark) what his experiences are with stock pipes. I've never done that before. A build for me has always included the pipe and carburetion to feed the "monsters" I've created.

Anyone know the ration of head flow to exhaust flow? Is is 60%?

Regards,
Gordon

[Big Jay]

An 836 will not cause leaking. As for blow-by that needs to be vented, you absolutely have to have cylinders bored by an expert ( not the local automotive shop) to best deal with this problem. Wiseco and JE are both excellent pistons. Wiseco can be set up a little tighter because of the material, 4032 vs 2618 for JE. The other big advantage of Wiseco and JE is the latest state of the art piston rings. Far superior than anything that was oem in the 70s.

As far as not being able to notice an 836 if the head is not done, simply not the case. If you take an engine with an inadaquate head like the Honds, and increase the displacement without increasing the breathing, you will not increase hoesepower. You simply take the power and move it down the RPM scale. This makes the motor feel like a stump puller. The increase in the low and mid range makes them very fun on the street. Add a Web cam and some of our springs and that will wake it up some on the top. There is, however, no substitute for increased breathing.

Best bang for the buck. If you could only do one, 836, or headwork, you would be much happier with the piston kit.

Jay

[SOHC steve]

Thanks for the relpies....at this stage I would really like to go the 836 kit with head work and a mild cam,not looking for a real beast,just something with a nice wide torque curve and power improvement,decent idle,you know the deal.As far as beefing up the engine goes,I guess the stronger studs,oil cooler and what about those rods...wil they be OKwith normal performance prep work (polish/shot peen etc) or should I go stronger? What model bikes did those stronger rods come from? I really think the Carillos would be overkill for a streeter,or are those stock rods really that weak? Will my stock 341 pipes kill the breathing,Im sure guys have run them on big bore engines before...comments?      Steve

[Sam Green Racing]

Steve, I have just found an old thread that was doing the rounds when I first joined the forum.

I gave it a bump and you should find it in the first few pages in this section.

It's titled 836 big bore and oil leaks.

Sam.

[JP]

Ilbikes, Gordon-

How do you seal the small 6mm studs above the spark plugs in the cam tower?  Please expand on this as I am putting my engine together right now.

JP

[RRRToolSolutions]

Blue Loctite. A very wise man taught me that. Absolute no leaks and still removable.

Gordon

[SOHC steve]

Steve, I have just found an old thread that was doing the rounds when I first joined the forum.

I gave it a bump and you should find it in the first few pages in this section.

It's titled 836 big bore and oil leaks.

Sam.

Hey Sam,thats good reading...did you modify your pistons to remove the excess flat areas? How did it turn out,do you think it helped? It seems to me that anything you can do to reduce the blow by/excess crankcase pressure the better...bigger breathers help obviuosly,but if you can fix he cause,so much the better.I think I will have a play with the thicker sleeve idea,I really think its a biiig ask on an air cooled engine to run thin sleeves in a aluminium block and expect really good sealing.It seems like the smaller big bore kits dont have the same hassles,so maybe the 836 is on the ragged edge of what can be done with a standard sleeve. I guess I keep reverting back to my experiences with other engine types....I used to build light aircraft engines years ago,they are air cooled,steel barrel,alloy head engines,but the typical bore had about.007" of taper in them to allow for expansion when at operating temp,without this taper they typically blew oil out the breathers and burned oil as well.The bores were 5" diameter,hence the huge amount of taper,but what Im getting at is there is a lot of expansion there in an air cooled engine and with the thin sleeves in the 836 it would probably exagerate the prob.The really definitive way of checking would be to do a "leakdown" type comp test when the engine is cold,warm and hot an see if the blow by gets worse and measure the crankcase pressure as well.
                Steve
     

[KB02]

The further I dive into the K8 that I have, the more ideas I keep coming up with. One idea wad an overbore kit... so this thread has been very interesting to me.

One question that I have, is has anyone had any experience with the Cycle-X 850 overbore kit? It's alot cheaper than the 836 kits that I have seen (most likely because of the pistons being cast rather than forged). What is the difference between cast rather than forged pistions? Obviously I know the forming differences (the way they are made), but how does that relate to being used in the engine?