Author Topic: Knock pins and cylinder stud packing rubbers F2 motor, advice please.  (Read 247 times)

0 Members and 1 Guest are viewing this topic.

Offline Old Moe Toe

  • Hot Shot
  • ***
  • Posts: 483
Between the cylinder block and the head on an F2 there are 4 knock pins and 8 cylindrical shaped rubbers that are called "Packing,cylinder stud" on the parts diagram. See first picture.
On the top surface of the cylinder block there are 8 holes that will accept both the knock pins and the 8 "Packing, cylinder studs". See picture 2.
I am interested in knowing which of the 4 holes the knock pins should actually be located in?. They will fit in all 8 of them but there are only 4 pins.
Also when seated in the holes the knock pins sit proud of the surface (see 3rd picture). I have not had the cylinder block machined. I have read on this forum somewhere that they should sit flush with the mating surfaces so wondering if I should shave them flush?. The gap from an eye measurement is about a mm and the head gasket I have is slightly thicker than that.
Pretty keen to only do this job once for now, so thanks in advance.
Brad

Offline 754

  • Really Old Timer ...
  • *******
  • Posts: 28,058
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #1 on: October 23, 2020, 06:48:01 pm »
Let's get this one sorted out, I would like to know as well..
Maker of the WELDLESS 750 Frame Kit
dodogas99@gmail.com
Kelowna B.C.       Canada

My next bike will be a ..ANFOB.....

It's All part of the ADVENTURE...

73 836cc.. Green, had it for 3 decades!!
Lost quite a few CB 750's along the way

Offline trigger

  • Enthusiast
  • **
  • Posts: 184
  • Engines built on reputation, not advertising.
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #2 on: October 24, 2020, 01:07:29 am »
The knock pins go through the head gasket and support the packing rubbers. If using a aftermarket head gasket which is thicker than the OEM one then, the rubbers will not seal to the head. The pins are fine as long as the rubbers are sealing the head. 

Offline onepieceatatime

  • Hot Shot
  • ***
  • Posts: 567
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #3 on: October 24, 2020, 04:24:33 am »
On my K5 and on my K7, there are 8 pins, and 8 rubbers, one of each for each hole. They are slightly proud of the holes, but I didn't try to measure by how much.

Sent from my Pixel 4 XL using Tapatalk

1972 CB750K
1974 CB450K7
1977 CB750K
1977 CB750K
1978 CB400A
1980 CB650C
1980 CB650
1982 CM450A
1997 GL1500SE

Offline madmtnmotors

  • When did I get to be a
  • Really Old Timer ...
  • *******
  • Posts: 5,673
  • Sunny Central Florida
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #4 on: October 24, 2020, 06:09:46 am »
The F2/F3 only require four since there are only four oil returns in the F2/F3 head as opposed to the eight oil returns on the K models. You will also need to be aware of the acorn head nuts and the copper head nut washers that are required at the four abandoned oil return locations. If memory serves, it is the four inner locations, but I'll try to find a pict to back up my spotty memory...  :o
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
                                           http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
                                           http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                           http://oldmanhonda.com/MC/wiring750K1.html
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline madmtnmotors

  • When did I get to be a
  • Really Old Timer ...
  • *******
  • Posts: 5,673
  • Sunny Central Florida
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #5 on: October 24, 2020, 07:31:47 am »
Okay, here ya go:



EZPZ  8)

If you are having trouble sorting the copper head nut washers from the steel ones a magnet might be able to help. A P.O. on one of my bikes used the acorn nuts and copper washers to attach the exhaust headers...

PHHBBBTTTT...  ::)

Note: You are only looking at the 1/2 side. The 3/4 will be similar in that the deleted oil return is the pair closest to the cam chain tunnel. NOT the closest set of cylinder studs, but the closest pair of studs where the barrel cutouts are in the cylinder block. The picture only shows one of the two oil returns that remain per side as opposed to the four per side on the K models.
« Last Edit: October 24, 2020, 07:36:10 am by madmtnmotors »
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
                                           http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
                                           http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                           http://oldmanhonda.com/MC/wiring750K1.html
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Old Moe Toe

  • Hot Shot
  • ***
  • Posts: 483
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #6 on: October 24, 2020, 05:03:18 pm »
Thanks for the replies.
It is interesting that some people leave the pins and packing rubbers out all together and say there is no issue doing this (see Brandens leak free top end sticky thread on this forum).http://forums.sohc4.net/index.php/topic,107040.0.html
As it had taken some time to get a response for this thread I had in the mean time decided to grind the knock pins flush with the top of the cylinder block as I was worried they may have prevented the head from sitting flat on the mating surface. My head needed to be machined flat as it was warped and perhaps the protruding knock pins were a possible reason. I had an extra 4 knock pins lying around so ground all 8 of them to be flush and thought it could do no harm to put them and the 8 packing rubbers in all 8 holes. Sure only 4 of them have oil returns in them but the other 4 are open to the atmosphere as the studs that go through them are open to the air and water on the F2/3 motors.
Maybe I am overthinking all this?. I don't know, this is what the shaved pins with the packing rubbers look like in situ (see first picture). The pins will not now stop the head from bolting down flat but now the packing rubbers sit just proud of the pins. Any comments here would be much appreciated.
« Last Edit: October 24, 2020, 10:50:31 pm by Old Moe Toe »

Offline madmtnmotors

  • When did I get to be a
  • Really Old Timer ...
  • *******
  • Posts: 5,673
  • Sunny Central Florida
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #7 on: October 25, 2020, 05:56:31 am »
You should be fine. Early models did not use these hence the discussions about whether they are necessary or not. Your understanding of the cylinder studs exposed to the atmosphere is correct and is the reason for the acorn nuts with copper washers to prevent weeping oil leaks at these four locations.
« Last Edit: October 25, 2020, 08:24:18 am by madmtnmotors »
TAMTF...


Wilbur



Projects:
"Evolution": http://forums.sohc4.net/index.php?topic=100352.0
"P.O. Debacle": http://forums.sohc4.net/index.php/topic,126692.msg1441661.html#msg1441661
F2/F3 O-rings: http://forums.sohc4.net/index.php?topic=113672.msg1300721#msg1300721
Cam Tower Studs: https://www.mcmaster.com/#93210a017/=t19sgp
Clean up that nasty harness: http://forums.sohc4.net/index.php?topic=137351.msg1549191#msg1549191
                                           http://forums.sohc4.net/index.php/topic,148188.msg1688494.html#msg1688494
                                           http://forums.sohc4.net/index.php/topic,139544.msg1579364.html#msg1579364
                                           http://oldmanhonda.com/MC/wiring750K1.html
Charging system diagnosis: http://forums.sohc4.net/index.php?topic=1012.msg8345#msg8345
Get the manuals: http://manuals.sohc4.net/cb750k/
The Dragon: http://forums.sohc4.net/index.php?topic=45183.msg1571675#msg1571675
Headlight Switch: http://forums.sohc4.net/index.php?topic=113986.msg1283236#msg1283236
Branden's leak free top end thread: http://forums.sohc4.net/index.php?topic=107040.0
Engine Lifting Made Easy: http://forums.sohc4.net/index.php/topic,58210.msg1684742.html#msg1684742
                                      http://forums.sohc4.net/index.php/topic,100352.msg1675840.html#msg1675840
Static and Dynamic Timing: http://www.hondachopper.com/garage/carb_info/timing/timing1.html
Airbox Gasket Replacement: http://forums.sohc4.net/index.php/topic,114485.msg1290000.html#msg1290000
"Café" : http://forums.sohc4.net/index.php/topic,84697.msg953814.html#msg953814
PD Carb Choke Linkage: http://forums.sohc4.net/index.php/topic,100352.msg1669248.html#msg1669248
                                    http://forums.sohc4.net/index.php/topic,110931.msg1248354.html#msg1248354
                                    http://forums.sohc4.net/index.php/topic,48858.msg515204.html#msg515204
Follow up on your damn posts: http://forums.sohc4.net/index.php/topic,144305.msg1791605.html#msg1791605
Taiwanese Cam Chain Tensioners:  http://forums.sohc4.net/index.php/topic,155043.msg1774841.html#msg1774841
Gumtwo Seat Cover: http://forums.sohc4.net/index.php/topic,164440.msg1897366.html#msg1897366
Primary Drive: http://forums.sohc4.net/index.php/topic,166063.msg1919278.html#msg1919278
Tank Latch: http://forums.sohc4.net/index.php/topic,165975.msg1919495.html#msg1919495
Shorten your forks: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-shorten-forks-td4042465.html DO NOT CUT THE SPRINGS!
Clutch How To: http://vintage-and-classic-honda-s.456789.n3.nabble.com/How-to-change-and-adjust-a-clutch-SOHC-td4040391.html
Late model K7/K8/F2/F3 front sprocket cover removal: http://forums.sohc4.net/index.php/topic,178428.msg2072279.html#msg2072279
630 to 530 conversion: http://forums.sohc4.net/index.php/topic,180710.msg2094423.html#msg2094423

Sent from my Tandy TRS-80!

Offline Jerry Rxman Griffin aka MuthaF'er

  • This MuthaF'er is getting to be a
  • Really Old Timer ...
  • *******
  • Posts: 14,202
  • Bought her new 4/75
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #8 on: October 25, 2020, 08:03:51 am »
Knock pins serve a purpose of locating/positioning the 2 pieces together correctly also
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline HondaMan

  • Someone took this pic of me before I became a
  • Really Old Timer ...
  • *******
  • Posts: 10,171
  • ...not my choice, I was nicknamed...
    • Getting 'em Back on the Road
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #9 on: October 25, 2020, 02:37:56 pm »
The knock pins (aka dowels) are used on the 4 oil return holes that DO NOT have the exposed cylinder studs. You can see the studs from outside the engine on 4 of them on these late heads.

Don't shorten the dowels: they help to hold back the crankcase pressure at high RPM by supporting the rubber dowel seals. This was started in the late K2 heads to prevent weeping at (then) Interstate 75 MPH speeds all day, especially caused by using too-thin oils (10w40).
The demons are repulsed when a man does good. Use that.
Blood is thicker than water, but motor oil is thicker yet...so, don't mess with my SOHC4, or I might have to hurt you.
Hondaman's creed: "Bikers are family. Treat them accordingly."

Link to Hondaman Ignition: http://forums.sohc4.net/index.php?topic=67543.0

Link to My CB750 Book: https://www.lulu.com/search?adult_audience_rating=00&page=1&pageSize=10&q=my+cb750+book

Link to website: www.SOHC4shop.com

Offline trigger

  • Enthusiast
  • **
  • Posts: 184
  • Engines built on reputation, not advertising.
Re: Knock pins and cylinder stud packing rubbers F2 motor, advice please.
« Reply #10 on: October 25, 2020, 11:55:27 pm »
The knock pins (aka dowels) are used on the 4 oil return holes that DO NOT have the exposed cylinder studs. You can see the studs from outside the engine on 4 of them on these late heads.

Don't shorten the dowels: they help to hold back the crankcase pressure at high RPM by supporting the rubber dowel seals. This was started in the late K2 heads to prevent weeping at (then) Interstate 75 MPH speeds all day, especially caused by using too-thin oils (10w40).

In the UK and europe, we never had the oil return dowels or the rubbers until the K6. Though the K2 was still in production for the UK and european market until early 1975, it still used the same barrels but the later head from the USA K3/K4  ;)