Author Topic: '78 750K first project by a car guy... (Read 34217 times)

RandyBMC · « **Reply #25 on:** July 10, 2015, 11:02:18 AM »

A few photos of the work lately. Just cleaning things up. I also cleaned the head, but haven't taken any photos of it just yet. I'm pretty happy with the way the cam cover is working out, but I plan to take the rouge and white to it still.

The cam cover was done with some steel brushes, a dremmel with brass wire wheels, a die grinder with steel wire wheels, and a Scotch Brite pad.

Hopefully I can get some funds put aside for the project to buy the rings, gaskets and machining soon.

HondaMan · « **Reply #26 on:** July 10, 2015, 10:13:43 PM »

For the rings: check on eBay for a seller named "Mrssuperdeals". I get good quality MC rings from there, usually about $25-$30 per set of 4, for the CB750K0-K6 engines.

RandyBMC · « **Reply #27 on:** July 10, 2015, 10:18:25 PM »

Thanks!

Will the K0-K6 rings work on the K8 pistons?

RandyBMC · « **Reply #28 on:** July 30, 2015, 03:41:34 PM »

Got the pistons off the rods and pulled all of the valves/retainers/springs from the head, boxed those, the head and the cylinder up and sent it all off to the machine shop today (Harold's Automotive Machine Shop in Richmond, TX)! Pretty excited to be making some progress.

Here are some photos of the work:

A little worried about this valve seat - coincidentally (or not), it is the same one that had the piston with the dent in the top. If it had been damaged, it was obviously reseated enough to allow the valve to close. Seems to me it was probably rebuilt for a valve issue of some sort in the past.

I can't wait to hear what Harold has to say. Looking forward to getting it back ready for reassembly!

Stev-o · « **Reply #29 on:** July 30, 2015, 05:17:44 PM »

Looks good Randy. Why Harold's? That's on the other side of the world from you.

RandyBMC · « **Reply #30 on:** July 30, 2015, 06:14:38 PM »

I have been told by more than one source that the guy is an artist, so I called him on the phone. I like the way the conversation went, so I shipped off my stuff. I couldn't get a good machine shop recommendation around where I'm located. I can always drive down if I need (or want) to, so I figured it was a good way to go.

HondaMan · « **Reply #31 on:** August 02, 2015, 08:22:32 PM »

Quote from: RandyBMC on July 10, 2015, 10:18:25 PM

Thanks!

Will the K0-K6 rings work on the K8 pistons?

Umm...not usually. There are some cheapie rings out there that do, but I don't use them, as they are Chinese knock-offs and not good quality. They may have the K8 rings, though, and Honda does in the stock sizes, too.

RandyBMC · « **Reply #32 on:** August 06, 2015, 09:30:24 AM »

Got word back from the machine shop. Not good news.

So that valve on number 3 had smacked the piston. The valve bent and hit the seat on the head. Pretty much what I had thought. When they replaced the valve, it was wron with the wrong keepers and retainer. The guide was cracked and it wasn't replaced.

Also, the cylinders need 1 over pistons.

So, I need to have the head and cylinders resurfaced, bore the cylinders, a valve job, and new intake and exhaust valves. That means new pistons are needed (with new rings, wrist pins, etc).

Question now:

CycleX has 2nd over pistons for $199, and they have the 836 Wiseco kit for $449. It includes the new head gasket too. Which one? This is a '78, so I'm worried that I may lose power with the non-domed pistons in the 2nd over kit. But my budget is now getting seriously stretched....

Input please. Thanks!

SOHC4 Cafe Racer Fan · « **Reply #33 on:** August 06, 2015, 09:51:47 AM »

The Wiseco 836 kit has higher compression and will give you a very noticeable performance gain. A port job will enhance that too, but increase your cost. With all that work I would go with the Wiseco for the incremental cost increase.

Stev-o · « **Reply #34 on:** August 09, 2015, 07:36:56 PM »

Sorry to hear the bad news, Randy. Another option is the ebay piston kit from Japan for $130.

There is a thread on here, quite a few guys have used it with success [even Hondaman]

http://www.ebay.com/itm/69-77-HONDA-CB750K-836cc-65mm-BIGBORE-PISTONS-KIT-W-HEAD-GASKET-CI-CB750KBB-/131421590213?hash=item1e995652c5&vxp=mtr

Bottom line, I would def go 836 if you have to bore. And FYI - around here, $50/hole is the going rate for boring.

madmtnmotors · « **Reply #35 on:** August 09, 2015, 08:26:03 PM »

Quote from: RandyBMC on August 06, 2015, 09:30:24 AM

CycleX has 2nd over pistons for $199, and they have the 836 Wiseco kit for $449. It includes the new head gasket too. Which one? This is a '78, so I'm worried that I may lose power with the non-domed pistons in the 2nd over kit. But my budget is now getting seriously stretched....

They also have 4th over (62mm, 761cc) for the same price ($199). I just completed a K8 rebuild with the 4th over CycleX pistons and it runs great. 500 mile break in complete and am working my way to the next oil change (1500-2000 mi). The dome on the K8 pistons is so slight that any loss in compression or power is probably offset by the slight increase in compression and displacement as a result of the overbore. I think it's a wash.

I'm satisfied with mine and would do it again. Mine can still be bored to 836cc (65mm) or 850cc (65.5mm) if so inclined.

RandyBMC · « **Reply #36 on:** August 10, 2015, 10:31:28 AM »

After reading 15 pages on the Japan 836 kit, I pulled the trigger on it. We'll see how it looks, but it sounds decent especially for my budget.

madmtnmotors · « **Reply #37 on:** August 10, 2015, 10:37:24 AM »

Quote from: RandyBMC on August 10, 2015, 10:31:28 AM

After reading 15 pages on the Japan 836 kit, I pulled the trigger on it. We'll see how it looks, but it sounds decent especially for my budget.

I've got a set of those too. In keeping with the "budget" theme of my most recent build, I opted for the 62mm (4th over) pistons since I figured I could use the stock cylinder studs with such a mild overbore. The 836 (65mm) pistons will go into my next build with HD cylinder studs, HD valve spring caps, and undercut gears.

SOHC4 Cafe Racer Fan · « **Reply #38 on:** August 10, 2015, 11:07:48 AM »

Note: a 4th over or a cruzinimage 836 kit will increase displacement -- but not compression. You will get an overall increase in power and torque, but not as much as with a high-compression kit like the Wiseco 836 kit.

madmtnmotors · « **Reply #39 on:** August 10, 2015, 12:06:28 PM »

Quote from: CB750 Cafe Racer Fan on August 10, 2015, 11:07:48 AM

Note: a 4th over or a cruzinimage 836 kit will increase displacement -- but not compression.

The compression increase is slight as a result of any overbore, provided there have been no changes to the combustion chamber (head). If we were talking about a 76' or older (just for comparison's sake) where you would be going from an old flat top piston to a new flat top piston, after the overbore you would be compressing a greater starting volume (increased cylinder volume as a result of the overbore) into the same size finished volume at TDC (provided the combustion chamber was not changed)

= a theoretical compression increase, even if it's just a little.

RandyBMC · « **Reply #40 on:** August 10, 2015, 01:16:45 PM »

I saw that - it should be a slight increase in compression. The machine shop is also decking the head and cylinders (just to have a perfect surface). The only worries I have there are cam timing and the size of the inserts for he oil passages - do I have to machine those the same distance as was removed from the cylinder? And with a stock cam and sprocket, how do I time the cam?

From what I gathered, here are the pertinent numbers and concerns for the Japan 836 kit:

Hand chamfer the oiling holes
Hand file the rings to .012" (about .5mm too big) which is about .002"-.003" more than stock ring gaps
Hand chamfer the holes on the wrist pin feeds underneath
Check for sharp edges on he piston skirt
With the microgrooves the new sets seem to have the piston clearance to the cylinder should be set to .0008"-.0012"
Torque the head stud nuts to 20 ft-lbs (corrected)
Use HD studs

calj737 · « **Reply #41 on:** August 10, 2015, 01:29:10 PM »

If you duck the head and block, the oil jets also need to be trimmed.

Head studs don't get "an extra" 20# of torque, they stay with the stock torque basically, but the nuts can see a little more. The torque of the stud into the block is determined largely in part by the metal/alloy of the threads.

If I recall correctly, 18# is the correct torque for these studs.

SOHC4 Cafe Racer Fan · « **Reply #42 on:** August 10, 2015, 01:34:04 PM »

Quote from: madmtnmotors on August 10, 2015, 12:06:28 PM

Quote from: CB750 Cafe Racer Fan on August 10, 2015, 11:07:48 AM
Note: a 4th over or a cruzinimage 836 kit will increase displacement -- but not compression.

The compression increase is slight as a result of any overbore, provided there have been no changes to the combustion chamber (head). If we were talking about a 76' or older (just for comparison's sake) where you would be going from an old flat top piston to a new flat top piston, after the overbore you would be compressing a greater starting volume (increased cylinder volume as a result of the overbore) into the same size finished volume at TDC (provided the combustion chamber was not changed)

= a theoretical compression increase, even if it's just a little.

Slight in comparison to 10.25:1.

madmtnmotors · « **Reply #43 on:** August 10, 2015, 01:43:46 PM »

Quote from: RandyBMC on August 10, 2015, 01:16:45 PM

The machine shop is also decking the head and cylinders (just to have a perfect surface). The only worries I have there are the size of the inserts for he oil passages - do I have to machine those the same distance as was removed from the cylinder?

You would only have to check these if they mill anything off the top of the head (the valve cover surface). Milling is usually only done to the bottom surface that mates to the cylinders. You can check the oil jets by inserting them in the head and use a straight edge to verify that the do not sit "proud" (above) the top of the head surface. If they do (not likely) a few passes with a hand file across the top should eliminate any potential interference with the cam tower. Only take off what is needed to make them flush. Again, I do not believe this would be necessary....

but I've been wrong before!

Quote from: RandyBMC on August 10, 2015, 01:16:45 PM

with a stock cam and sprocket, how do I time the cam?

You could grind the bolt holes in the stock sprocket into an oblong shape. The alternative would be to procure an adjustable cam sprocket with the holes already slotted ($35 from A.P.E). I would install the stock sprocket first and check the cam lobe degrees. If they are off by more than a couple of degrees then you can decide whether you want to slot the stock sprocket or buy one already slotted.

Quote from: RandyBMC on August 10, 2015, 01:16:45 PM

From what I gathered, here are the pertinent numbers and concerns for the Japan 836 kit:

Hand chamfer the oiling holes
Hand file the rings to .012" (about .5mm too big) which is about .002"-.003" more than stock ring gaps
Hand chamfer the holes on the wrist pin feeds underneath
Check for sharp edges on he piston skirt
With the microgrooves the new sets seem to have the piston clearance to the cylinder should be set to .0008"-.0012"
Torque the head studs and extra 20 ft-lbs
Use HD studs

Yep, that's pretty much what I gathered as well, but the torque reading is misrepresented. The new torque value for HD studs would be 20 ft/lbs. If you were to use an extra 20 ft/lbs then your torque value would be 35 ft/lbs (15 ft/lbs plus an extra 20 ft/lbs would be 35 ft/lbs). Way too high.

I suggest that the extra torque only be applied to the HD studs (which appears to be implied). Some have applied higher torque to the stock studs without problems, while others have snapped them off at stock torque

calj737 · « **Reply #44 on:** August 10, 2015, 01:55:01 PM »

A little clarification: randy are you referring to the knock pins between the cylinders and the head, or the oil passages? My reference was to trimming the knock pins, but said oil jets (550 feature). Wilbur is correct, the oil passages are in the head above..

madmtnmotors · « **Reply #45 on:** August 10, 2015, 02:06:19 PM »

Quote from: calj737 on August 10, 2015, 01:55:01 PM

A little clarification: randy are you referring to the knock pins between the cylinders and the head, or the oil passages? My reference was to trimming the knock pins, but said oil jets (550 feature). Wilbur is correct, the oil passages are in the head above..

Oh yeah! Most definitely check ALL dowels (or knock pins) for proper length. You can test fit the head, or break out the calipers measuring the dowel lengths vs the dowel bore depths.

RandyBMC · « **Reply #46 on:** August 10, 2015, 02:10:31 PM »

Knock pins. I believe I even read at one point that the knock pins weren't totally necessary (maybe at the Cycle X website?), but I would rather use them.

I believe it was HondaMan that said the torque value should be given an extra 20 ft-lbs, and I believe I may have misspoke. It would be the torque of the nut on the stud, not the stud itself.

madmtnmotors · « **Reply #47 on:** August 10, 2015, 02:20:46 PM »

Quote from: RandyBMC on August 10, 2015, 02:10:31 PM

Knock pins. I believe I even read at one point that the knock pins weren't totally necessary (maybe at the Cycle X website?), but I would rather use them.

Those would be the dowels where the rubber "barrel" seals are used at the oil returns. I'm with you, I would use them too. There are also two alignment dowels at the front corners between the head and cylinders. I highly recommend that those be used.

All dowels, whether at the oil returns or at the alignment dowel position, should be checked for length. The knock pins (at the oil returns) should finish flush with the head surface. They could extend above, but no more than the compressed thickness of the head gasket! I would just make sure they finish flush.

As for the alignment dowels, they must extend into both the cylinders and up into the head. Here is where I add the bores in the head and cylinders and compare them to the length of the dowel.

Quote from: RandyBMC on August 10, 2015, 02:10:31 PM

I believe it was HondaMan that said the torque value should be ~~given an extra~~ 20 ft-lbs, and I believe I may have misspoke. It would be the torque of the nut on the stud, not the stud itself.

Correct.

RandyBMC · « **Reply #48 on:** August 10, 2015, 05:13:48 PM »

Since I got such a great deal on the pistons from asking here - any good suggestions on heavy duty valve spring retainers?

Retro Rocket · « **Reply #49 on:** August 10, 2015, 05:19:54 PM »

Try APE Engineering, they have titanium retainers for our bikes.. Half way down the page.

http://cbrzone.com/sohc.html

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Author Topic: '78 750K first project by a car guy... (Read 34217 times)