Topic: 836 Clearance? Thicker head or base gasket???

[HondaMan]

Don, I actually could use a lil' levity as this "cheap" kit is TAXING my brain.

Ok, I procrastinated tearing the top back down in hopes those little gnomes or elves or whatever that fixed all the cobbler's shoes as he slept would appear. Didn't happen.

First, to shut Terry up about my machinist (no offense, mate- actually, thanks for getting me off my arse...)
Got three other heads laying about the shop, so I measured them:
K1: 3.343"
K3: 3.341"
K3: 3.339"
The one in question:
K5: 3.337" (that's post deck, Terry!)
I measured the piston above deck height and got .013" as I had guessed with Don's info.

Here ya go Don- the root of the problem:
Measured some stock pistons and these from the top of the pin bore to shoulder. I went for the smallest numbers (closest to edge) on both as getting a reference point due to diameter difference was difficult (as in using the circlip to stop the caliper won't work 'cause it's deeper in the 836):
Stock: .664"-.666"
836:   .679"-.680"
A .013"-.016" difference.

My base gasket was .019-.020" post-squish.

So what's the fix?

HM, by turning the shoulders do you mean it that simply? Turn a 2mm band by .013" cut around the shoulder and that's that? Or would the cut need blending or ramping (for lack of better words)? Would adding a .015" Cometic base to a Honda or Vesrah base cure my ills?

The simpler approach would be the base gasket shims, like MRieck's describing. And, yes, the band can be cut off, like with a Prototrak, but I would certainly smooth off the edges outside with some 80 grit and the edges inside with a small rounded file, just to reduce their sharpness.

All this said, I just got 2 more sets of those 836 pistons in (still in their wrapping), might have to go measure them. I also have one set of the "old" ones from May of this year, will have to measure them and see if they are now different. When did you get yours? I sure haven't seen this before now.

[Terry in Australia]

Don, I actually could use a lil' levity as this "cheap" kit is TAXING my brain.

Ok, I procrastinated tearing the top back down in hopes those little gnomes or elves or whatever that fixed all the cobbler's shoes as he slept would appear. Didn't happen.

First, to shut Terry up about my machinist (no offense, mate- actually, thanks for getting me off my arse...)
Got three other heads laying about the shop, so I measured them:
K1: 3.343"
K3: 3.341"
K3: 3.339"
The one in question:
K5: 3.337" (that's post deck, Terry!)
I measured the piston above deck height and got .013" as I had guessed with Don's info.

Here ya go Don- the root of the problem:
Measured some stock pistons and these from the top of the pin bore to shoulder. I went for the smallest numbers (closest to edge) on both as getting a reference point due to diameter difference was difficult (as in using the circlip to stop the caliper won't work 'cause it's deeper in the 836):
Stock: .664"-.666"
836:   .679"-.680"
A .013"-.016" difference.

My base gasket was .019-.020" post-squish.

So what's the fix?

HM, by turning the shoulders do you mean it that simply? Turn a 2mm band by .013" cut around the shoulder and that's that? Or would the cut need blending or ramping (for lack of better words)? Would adding a .015" Cometic base to a Honda or Vesrah base cure my ills?

Thanks mate, do you have another cylinder block to compare yours to? (I was actually questioning the amount taken off your block, not your head?) Anyway, I can't help but wonder why the manufacturer of those cheap 836 kits got the height wrong? I guess it's another one of those "you get what you pay for" lessons? Cheers, Terry.

[Don R]

I guess the question is did they change the piston or did a couple of us just have an unfortunate tolerance stack? It's easy enough to shim the cylinder, if you're going to be a big boy engine builder, things like this pop up. Literally.

[Terry in Australia]

I guess the question is did they change the piston or did a couple of us just have an unfortunate tolerance stack? It's easy enough to shim the cylinder, if you're going to be a big boy engine builder, things like this pop up. Literally.

Hmmnnnn, no offence Don, but I don't think too many "Big Boy Engine Builders" would be using those kits. Cheers, Terry.

[Brantley]

The simpler approach would be the base gasket shims, like MRieck's describing. And, yes, the band can be cut off, like with a Prototrak, but I would certainly smooth off the edges outside with some 80 grit and the edges inside with a small rounded file, just to reduce their sharpness.

All this said, I just got 2 more sets of those 836 pistons in (still in their wrapping), might have to go measure them. I also have one set of the "old" ones from May of this year, will have to measure them and see if they are now different. When did you get yours? I sure haven't seen this before now.

I'm weighing both options. I like the simpler fix, but only buying one base gasket next I tear the top down would probably be the smarter option. If you consider May the "old" ones I'd definitely recommend whipping the calipers out: I got mine first week of March, this year. The sticker on the box reads, "C I CB750KPS", if that helps. I think I might post a heads up for folks that haven't fitted theirs, yet, to check 'em.

Thanks mate, do you have another cylinder block to compare yours to? (I was actually questioning the amount taken off your block, not your head?) Anyway, I can't help but wonder why the manufacturer of those cheap 836 kits got the height wrong? I guess it's another one of those "you get what you pay for" lessons? Cheers, Terry.

Ahhh, another failed attempt at being a smartarse and interjecting a bit of humor... I actually meant "cylinder". I get confused enough under a pile of numbers... add wordz? Forget it. I AM paying for it now, to be sure. I did recently read one of HM's posts about receiving a set of Wiseco pistons that had no wrist pin oil holes drilled. I sure would be a lot more pissed off spending four or five times what I did on these and still have to monkey around with finish and fit...

I guess the question is did they change the piston or did a couple of us just have an unfortunate tolerance stack? It's easy enough to shim the cylinder, if you're going to be a big boy engine builder, things like this pop up. Literally.

Hmmnnnn, no offence Don, but I don't think too many "Big Boy Engine Builders" would be using those kits. Cheers, Terry.

Don, the fun police from down under might not have caught that, but I did. Lemme know what fix route you take and the results. I'll post mine when it happens.

Thanks again, all, this has been a huge help.

[Don R]

You might notice I didn't say professional engine builder Terry. Jeez, someone woke up grumpy. Where is the sarcasm or humor alert button? Will do Brantley, I've been in the house sick so far this week. bleagh.

[CB750F2]

I have been watching this post with interest and concern as I am in the process of replacing standard F2 pistons with the cheap 836 pistons. I have measured the height of my F2 barrels  and a spare. They are both 3.344". I received my
pistons in early July this year. This morning I compared the F2 piston with one of the new 836 pistons by joining them together with a piston pin and eye balling the top edges. They look very close to being equal. If anything the 836 piston is a little lower. I did the same comparison with a 392 piston and it is obvious that the 392 is lower than the F2 piston by around a millimeter. I have attached a photo showing the comparison. It is a pity that I don't have a 300 piston for comparison.
          I hope this helps. Pat

[Don R]

Good idea! I can do that too. I have 836kit, stock 750 and 812 kit f2 pistons loose at the moment.

[Terry in Australia]

I have been watching this post with interest and concern as I am in the process of replacing standard F2 pistons with the cheap 836 pistons. I have measured the height of my F2 barrels  and a spare. They are both 3.344". I received my
pistons in early July this year. This morning I compared the F2 piston with one of the new 836 pistons by joining them together with a piston pin and eye balling the top edges. They look very close to being equal. If anything the 836 piston is a little lower. I did the same comparison with a 392 piston and it is obvious that the 392 is lower than the F2 piston by around a millimeter. I have attached a photo showing the comparison. It is a pity that I don't have a 300 piston for comparison.
          I hope this helps. Pat

Thanks Pat, it's good to see someone posting nice clear pics which positively illustrate the problem, and not have to interpret the technically incorrect ramblings of those poor silly buggers from across the pond. With their lack of attention to detail and poor communication skills, it's no wonder they're always in so much trouble!

Now while those slugs would work in your F2, you can clearly see from your pics that your compression ratio is going to fall through the floor if you do. Considering that big bore kits are available for F2's from CycleX etc for not too much money now, why would you want to? You're not considering a turbo application are you? Cheers, Terry.

[CB750F2]

Terry, the stock compression ratio for the F2 is 9.0:1. The 836 kit will still give me 9.0:1 because these pistons are compressing a much bigger volume than standard into a slightly bigger combustion chamber. I realise that with an 836 kit with domed shaped pistons the compression ratio will be in excess of 10.0:1. I am OK with the lower CR because I am looking for a good reliable motor that runs the way it should rather than a high performance machine. I will be also be taking a small cut off the head so I will recover some of the lost compression. I was not prepared to spend the extra dollars for the dome shaped kit.
Terry, I would agree with you about the CR dropping through the floor if I was replacing standard bore F2 pistons with flat topped ones from the K models but that's not what I am doing. Thanks, Pat

[Terry in Australia]

No worries Pat, as much as I doubt the 9.0:1 CR figure that's been bandied about, and as much as I know first hand that a good F2 engine loves 10.25:1 or higher compression with no affect on reliability or longevity, I'll concede that these pistons are cheap, and if you're on a budget, they're a good deal. Cheers, Terry.

[dave500]

i cant help with 750 info but use plasticene,oil the piston and combustion chamber so it dosent stick,rotate the engine over a few cycles,this is a 500 with xl125 pistons which are domed the 500 ones are flat but share the same gudgeon height,i ended up having the combustion chambers milled out as the edge of the piston ran too close to the head with the stock gasket like 3 thou,the valves cleared well going by the little pricks i dug into the plasticene,,before terry says anything smart im a bit of a little prick myself.


it can be seen here how the outer edge plasticene has peeled away as the head has been lifted off,it turned over fine by hand,this is too close and carbon and expansion will soon close the minimal clearance,,just because it turns over freely isnt a 100% its ok,,this must be checked and seen.

[Terry in Australia]

As long as you're happy Dave, that's the main thing.

[dave500]

ha!the main thing is that brantleys engine dosent prove to be short lived through a rushed or mis guided assembly.

[Brantley]

Thanks Pat, it's good to see someone posting nice clear pics which positively illustrate the problem, and not have to interpret the technically incorrect ramblings of those poor silly buggers from across the pond. With their lack of attention to detail and poor communication skills, it's no wonder they're always in so much trouble!

Terry, Stop with the sweet talk, you'll make me blush. Would not a lack of attention to detail mean I had not noticed something amiss and not started this thread, thereby precluding you from further vaulting your post count into the stratosphere? Hmmm? Now go listen to Colin Hay's latest solo record (whenever that was- we across the pond stopped caring in '82). Take that!

ha!the main thing is that brantleys engine dosent prove to be short lived through a rushed or mis guided assembly.

Thanks for the pix and input, Dave. Again, if I were rushing I would have glossed over it with the fact that it turned without hitting the HEAD. If I decide to have the shoulders turned I will "clay" the pistons. I don't see the need if I stack base gaskets and the shoulders are no longer proud of the deck, as the dome is the same shape as stock and the valve reliefs are on the order of .024" deeper than stock on the intake side and .015" exhaust.

[Terry in Australia]

Terry, Stop with the sweet talk, you'll make me blush. Would not a lack of attention to detail mean I had not noticed something amiss and not started this thread, thereby precluding you from further vaulting your post count into the stratosphere? Hmmm? Now go listen to Colin Hay's latest solo record (whenever that was- we across the pond stopped caring in '82). Take that!

Ha ha, I thought you were serious for a minute, as I think Colin Hay (who's a nice bloke for a Scotsman, but what's that got to do with anything?) has just released a new record?

Now I don't know if you're entitled to a "Attention to detail" award for noticing that your pistons are thumping into your head when you turn the engine over though, lets face it, you would have eventually found out when you'd installed your camshaft and rockers anyway, although to be fair you probably would've assumed that you'd fcuked up your cam timing?

Speaking of cam timing, what's your plan for correcting your cam timing, which will probably be off a little after you stack several base gaskets under the cylinder block, are you gonna slot the holes in your cam sprocket slightly and use a degree wheel to dial in your cam? I expect that you were going to anyway as you're probably going to run a higher lift cam to get all the benefits of Mike's head? Anyway, all the best mate, I'm looking forward to seeing a youtube clip of that baby running! Cheers, Terry.

[HondaMan]

Just to add to the general numerical 'din': I measured the F2 I'm doing now, which has not the 836 pistons, but their [prettier] Z1 Enterprises little brothers, in 1.00mm oversize. The cylinders are 3.353" tall. The pistons are -0.007" from the deck. These pistons' shoulders match exactly the same height as the June 836 set I last had, as I did the wristpin-to-crown side-by-side test on them when they arrived.

BTW: By going to 1.00mm oversize and milling the head 1.08mm in the rebuild, it comes back to 9.0:1 CR. The chambers cc out to 22.7cc volume. Since the F2/3 head added about 1.00mm between the edge of the larger intake valve and the high-dome piston, this make sense. I have conflicting specs (even from Honda(!) about the CR on these bikes. Some say 9.2:1, some 9.6:1, and some 9.0:1. 

I suppose one value is the dynamic compression, one is the static compression, and one is a mistake in marketing?

[Brantley]

Terry, Stop with the sweet talk, you'll make me blush. Would not a lack of attention to detail mean I had not noticed something amiss and not started this thread, thereby precluding you from further vaulting your post count into the stratosphere? Hmmm? Now go listen to Colin Hay's latest solo record (whenever that was- we across the pond stopped caring in '82). Take that!

Ha ha, I thought you were serious for a minute, as I think Colin Hay (who's a nice bloke for a Scotsman, but what's that got to do with anything?) has just released a new record?

Now I don't know if you're entitled to a "Attention to detail" award for noticing that your pistons are thumping into your head when you turn the engine over though, lets face it, you would have eventually found out when you'd installed your camshaft and rockers anyway, although to be fair you probably would've assumed that you'd fcuked up your cam timing?

Speaking of cam timing, what's your plan for correcting your cam timing, which will probably be off a little after you stack several base gaskets under the cylinder block, are you gonna slot the holes in your cam sprocket slightly and use a degree wheel to dial in your cam? I expect that you were going to anyway as you're probably going to run a higher lift cam to get all the benefits of Mike's head? Anyway, all the best mate, I'm looking forward to seeing a youtube clip of that baby running! Cheers, Terry.

Cam... tie... ming...? Do I have to wind it like a watch? Or is that chain thingy like the bits in a grandfather clock?

[Terry in Australia]

Cam... tie... ming...? Do I have to wind it like a watch? Or is that chain thingy like the bits in a grandfather clock?

Dunno mate, I wear a digital watch. Hey I forgot to check, how did your ebay auction go for your K0? Cheers, Terry.

[Kickstart]

Just to add to the general numerical 'din': I measured the F2 I'm doing now, which has not the 836 pistons, but their [prettier] Z1 Enterprises little brothers, in 1.00mm oversize. The cylinders are 3.353" tall. The pistons are -0.007" from the deck. These pistons' shoulders match exactly the same height as the June 836 set I last had, as I did the wristpin-to-crown side-by-side test on them when they arrived.

BTW: By going to 1.00mm oversize and milling the head 1.08mm in the rebuild, it comes back to 9.0:1 CR. The chambers cc out to 22.7cc volume. Since the F2/3 head added about 1.00mm between the edge of the larger intake valve and the high-dome piston, this make sense. I have conflicting specs (even from Honda(!) about the CR on these bikes. Some say 9.2:1, some 9.6:1, and some 9.0:1. 

I suppose one value is the dynamic compression, one is the static compression, and one is a mistake in marketing?

Was the 22.7cc volume after the 1.08mm milling, or before?
I'm getting approximately 22.5cc (as best I can measure) in my F0 head after a 0.005" mill and some de-shrouding/quench band dremel work.  I guess the stock F2/3 chamber is a lot larger if you're getting a similar volume reading after milling that much off.

Sorry about the Hijak

I'm really enjoying this thread... I'm also looking forward to Brantley getting this worked out.

[Terry in Australia]

I guess the stock F2/3 chamber is a lot larger if you're getting a similar volume reading after milling that much off.

The F2/3 combustion chamber is huge compared to your F chamber mate, which is the root cause of my cynicism regarding the 9:1 CR figure quoted by Pat and others using those flat top pistons in an F2/3. Here's a link to a pic of Dynoman's new 10.5:1 CR 836cc F2/3 pistons, check out the dome on these beauties, if those flat tops are really 9:1 CR in an F2, then the Dynoman slugs are obviously under-rated......... http://www.dynoman.net/images/engine/piston/DP836/2010version/DP836-4.jpg

[CB750F2]

      OK, my F2 manual says the CR of the F2 is 9.0. Using that piece of information and the swept volume of each cylinder the combustion chamber volume is calculated as 23.0cc. I started to calculate the combustion chamber using flat topped pistons and was coming up with a figure close to 26cc. At this point I was in contact with Mark(HM) who confirmed that the combustion chamber volume using flat topped pistons was indeed 26cc. This gives a CR of a little greater then 9.0. In my case I am also taking 0.015" off the head which will increase it a little more.
      I will be away for a few weeks but when I return I intend to cc the combustion chambers after the milling has been done. I will do the four chambers. This will confirm the CR and also check to see if they are all equal. If there is a problem with CR it can be fixed at this point without too much trouble. The ccing of the combustion chanbers has probably been done many times by others but I will do it anyway to satisfy my curiosity and to make sure that they are equal. Thanks, Pat

[Don R]

I cut the head .010, finished the quench  band and assembled the engine, with the F model cam installed straight up. I used plumbers putty to clay the pistons. The thinnest puty looked to be about .055 thick at the valves. I checked it 3* advanced too. looked good and the edges were fine so I'm gonna put it together. The APE adjustable timing gear and cylinder studs worked great.

[CB750F2]

OK we are back from our trip to Canadaand the US I said before we left that I would CC the combustion chambers when we returned. I have done that as well as measureing/calculating the volume of the dome of a 61mm F2 piston. The combustion chamber volume measured 28.5cc and the dome volume measured/calculated to be 9.35cc. The volumes were measured using a Burette.
Attached are two work sheets. One is used to calculate the CR using 61mm bore F2 pistons and the other to calculate the CR using the flat topped 836 pistons.
It would be good if someone else repeated the tests to confirm or otherwise my results.
The results are surprising - to me anyway.
I will probably assemble the top end and measure piston to valve clearance to see how much can be milled off.
Another option is to find a set of standard bore cylinders and reuse my F2 pistons.
PS
The system will not allow me to post attachments.
Thanks, Pat

[CB750F2]

I was unable to post the attachments in my previous reply. The CR using 61mm F2 pistons calculated out to 9.0 to 1 and the CR using the flat topped 836 pistons calculated out to 7.65 to 1. Thanks, Pat