Author Topic: 75 Super Sport Pistons  (Read 11749 times)

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Online MRieck

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Re: 75 Super Sport Pistons
« Reply #25 on: January 27, 2016, 04:52:16 AM »
If anything the -392 head has fewer cc's and will bump your compression slightly not decrease it. The -392 engine is 9.2:1 and the head is part of that reason. Now, my disclaimer, I have not measured combustion chambers but have owned a 75 750F for 41 years.
Don't have to cc a chamber Jerry....you can tell just by looking at it. ;)
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Offline BPellerine

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Re: 75 Super Sport Pistons
« Reply #26 on: January 27, 2016, 05:38:49 PM »
If anything the -392 head has fewer cc's and will bump your compression slightly not decrease it. The -392 engine is 9.2:1 and the head is part of that reason. Now, my disclaimer, I have not measured combustion chambers but have owned a 75 750F for 41 years.
Don't have to cc a chamber Jerry....you can tell just by looking at it. ;)
I may be wrong but compared to a ko head the 78 392 head looks to have been decked a little to get compression.billp
1978 CB 750K ard and webers
another anfob

Offline RodSOHC750

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Re: 75 Super Sport Pistons
« Reply #27 on: January 29, 2016, 01:17:52 PM »
Any carb modifications with the 836cc conversion?  Carbs have stock #105 jets.  A rebuild kit I bought includes #110 jets.
1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline HondaMan

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Re: 75 Super Sport Pistons
« Reply #28 on: January 29, 2016, 05:55:49 PM »
Any carb modifications with the 836cc conversion?  Carbs have stock #105 jets.  A rebuild kit I bought includes #110 jets.
No. The airflow ratios remain the same, unless you change either the cam, or the size of the inlet valve. That said, many people change to different jets just 'cuz they want to.

Most of the Keyster kits I have seen lately (if that's what yours is?) have come with #110 mainjets, but they have different taper entry vents, so they act leaner than #110 size, confusing the issue. Stick with genuine Keihin jets: hard to find right now, but they are around.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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

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Offline RodSOHC750

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Re: 75 Super Sport Pistons
« Reply #29 on: January 29, 2016, 06:07:26 PM »
I have K&L carburetor kits. 
1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline Kawahonda

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Re: 75 Super Sport Pistons
« Reply #30 on: January 29, 2016, 10:15:47 PM »
I think K&L and Keystar are very compatible if not the same parent company, but Hondaman could confirm.

I'd trust the washers and the o-rings...maybe the gaskets...but nothing else.

Offline Jerry Rxman Griffin aka MuthaF'er

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Re: 75 Super Sport Pistons
« Reply #31 on: January 29, 2016, 10:58:36 PM »
Compare the air screws. Holes or no holes?! Don't think I'd worry about the mains. I'd guarantee the needles are not as smooth or the same -392 profile as the F.
As of today 3/13/2012 my original owner 75 CB750F has made it through 3 wives, er EX-wives. Free at last.  ;-)

Offline RodSOHC750

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Re: 75 Super Sport Pistons
« Reply #32 on: February 01, 2016, 11:29:24 PM »
I have been unsuccessful so far in locating a piston kit for the 836cc conversion that maintains the stock compression ratio of 9.5 and under $250.  As a fall back, I am able to locate 61.5mm pistons. 
1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline SOHC4 Cafe Racer Fan

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Re: 75 Super Sport Pistons
« Reply #33 on: February 01, 2016, 11:41:56 PM »
Rod,
Cruzinimage on eBay.
1975 CB550K1 "Blue" Stockish Restomod (http://forums.sohc4.net/index.php?topic=135005.0)
1975 CB550F1 frame/CB650 engine hybrid "The Hot Mess" (http://forums.sohc4.net/index.php/topic,150220.0.html)
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Offline Retro Rocket

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Re: 75 Super Sport Pistons
« Reply #34 on: February 03, 2016, 02:36:48 PM »
I have been unsuccessful so far in locating a piston kit for the 836cc conversion that maintains the stock compression ratio of 9.5 and under $250.  As a fall back, I am able to locate 61.5mm pistons.

Rod, you'd better be quick mate....

http://forums.sohc4.net/index.php/topic,154912.0/topicseen.html
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline Kawahonda

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Re: 75 Super Sport Pistons
« Reply #35 on: February 04, 2016, 10:45:49 AM »
Yeah, what retro said.

But I wonder why the Cruizin image kit is no longer on eBay. The dude had 10+ left and the next couple days it's no longer there. I'd email the seller and ask him.

Offline Ilja

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Re: 75 Super Sport Pistons
« Reply #36 on: February 04, 2016, 11:58:30 AM »
Ok, from a guy with a very modified cb836 turbo, my view on the subject... spend a little bit more money and buy the 0.5mm oversize pistons if you have no interest in tuning.

The 836cc kit is nice, but requires 4mm of boring which will cost you more than a normal 0.5mm overbore.
The sleeves will be very thin after boring... to be honest, to my opinion it is really on the edge. My 836cc is running ok so far, but I'm afraid if I will push it hard, the sleeves will deform because they can't take as much heath as sleeves that are e.g. 2.5mm thick.
Also, if you screw up, you can't go bigger. So in that case you will need new cylinders or resleeving ($$).

If you don't want too complicate things, don't go up and just stay with stock.
If you like to experiment (like I do hehe), go ahead and buy the kit. ;-)

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Re: 75 Super Sport Pistons
« Reply #37 on: February 04, 2016, 04:33:16 PM »
I have been unsuccessful so far in locating a piston kit for the 836cc conversion that maintains the stock compression ratio of 9.5 and under $250.  As a fall back, I am able to locate 61.5mm pistons. 

Rad: Did you write to me about the cost of modifying the DOHC750 (62mm) pistons to use in "F" engines? I just got my set back: he charged $60 for it.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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 madmtnmotors

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Re: 75 Super Sport Pistons
« Reply #38 on: February 04, 2016, 08:05:36 PM »
I have been unsuccessful so far in locating a piston kit for the 836cc conversion that maintains the stock compression ratio of 9.5 and under $250.  As a fall back, I am able to locate 61.5mm pistons. 

Rad: Did you write to me about the cost of modifying the DOHC750 (62mm) pistons to use in "F" engines? I just got my set back: he charged $60 for it.


I was at least one of those that had reached out inquiring about those. That's not a bad price. If it still holds once I get my 79' motor torn down and am able to asses the condition of the pistons I will likely be reaching out to you again. Thanks Mark!
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
                                          
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 HondaMan

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Re: 75 Super Sport Pistons
« Reply #39 on: February 05, 2016, 07:45:59 PM »
I have been unsuccessful so far in locating a piston kit for the 836cc conversion that maintains the stock compression ratio of 9.5 and under $250.  As a fall back, I am able to locate 61.5mm pistons. 

Rad: Did you write to me about the cost of modifying the DOHC750 (62mm) pistons to use in "F" engines? I just got my set back: he charged $60 for it.


I was at least one of those that had reached out inquiring about those. That's not a bad price. If it still holds once I get my 79' motor torn down and am able to asses the condition of the pistons I will likely be reaching out to you again. Thanks Mark!

Ah...I knew it was SOMEone here: I get so much e-mail now that I often can't find who it was who asked me, a month later!
Just let me know if you want to send some: it always takes him a while to do them, as he waits until it is slow in his shop, and nothing is in the lathe.
See SOHC4shop@gmail.com for info about the gadgets I make for these bikes.

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 madmtnmotors

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Re: 75 Super Sport Pistons
« Reply #40 on: February 05, 2016, 08:13:41 PM »
Ah...I knew it was SOMEone here: I get so much e-mail now that I often can't find who it was who asked me, a month later!
Just let me know if you want to send some: it always takes him a while to do them, as he waits until it is slow in his shop, and nothing is in the lathe.

These would be for future use, so turnaround time is not critical.
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
                                          
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 RodSOHC750

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Re: 75 Super Sport Pistons
« Reply #41 on: February 27, 2016, 12:14:06 PM »
Well, I bought a set of .5mm oversize pistons for a 1975 750K for my 1975 750F.  There are apparent differences namely in the valve recesses and the F pistons having a slightly higher deck height.  Trying to figure if I should machine the new pistons valve recesses. 

1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline RodSOHC750

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Re: 75 Super Sport Pistons
« Reply #42 on: February 27, 2016, 12:18:57 PM »
Also, I notice the top edge of the F piston is beveled where the K piston is not.
1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline BPellerine

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Re: 75 Super Sport Pistons
« Reply #43 on: February 27, 2016, 05:25:13 PM »
check the the pistons for height diff by putting a wristpin in both the f and k pistons side by side,chances are the f pistons have deeper valve recess cause they are taller,you should not have to machine the k pistons.billp
1978 CB 750K ard and webers
another anfob

Offline RodSOHC750

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Re: 75 Super Sport Pistons
« Reply #44 on: February 27, 2016, 07:11:35 PM »
I compared the two pistons side by side with the upper ring in both piston grooves.  As you run your finger tip along the piston top from one piston to another, you can feel the F piston is slightly higher. 

I don't want to reduce the 750 F's 9.2:1 compression ratio.  Will the K piston affect the compression ration being it is slightly shorter but has less valve recess volume. 

1979 Honda CB750L Limited Edition
1975 Honda CB750F Super Sport
1972 Honda CL450
1970 Honda CT70

Offline Retro Rocket

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Re: 75 Super Sport Pistons
« Reply #45 on: February 27, 2016, 09:50:15 PM »
I compared the two pistons side by side with the upper ring in both piston grooves.  As you run your finger tip along the piston top from one piston to another, you can feel the F piston is slightly higher. 

I don't want to reduce the 750 F's 9.2:1 compression ratio.  Will the K piston affect the compression ration being it is slightly shorter but has less valve recess volume.

To check the piston height you have to do as Bill said, put the wrist pin in both pistons, side by side,  then measure...
750 K2 1000cc
750 F1 970cc
750 Bitsa 900cc
If You can't fix it with a hammer, You've got an electrical problem.

Offline madmtnmotors

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Re: 75 Super Sport Pistons
« Reply #46 on: February 28, 2016, 06:39:02 AM »
I don't want to reduce the 750 F's 9.2:1 compression ratio.

Then you are going to have to pony up for a set of Wiseco 10.25:1 836cc pistons.

Otherwise, deal with a little loss of compression by using K model pistons.
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
                                          
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 Stev-o

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  • Central Texas
Re: 75 Super Sport Pistons
« Reply #47 on: February 28, 2016, 07:47:57 AM »
As a proud owner of an 836cc motor, I highly recommend it. 
'74 "Big Bang" Honda 750K [836].....'76 Honda 550F.....K3 Park Racer!......and a Bomber!............plus plus plus.........

Offline Kawahonda

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Re: 75 Super Sport Pistons
« Reply #48 on: February 28, 2016, 09:21:38 AM »
There are lots of conflicting information in this thread (and in your other). Earlier part of thread says no compression loss with k Pistons. Some say gain. Now, the fact is that f pistons are not the same as k Pistons all along.

I guess the truth is that you should order some NOS oversized ones...

Offline BPellerine

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Re: 75 Super Sport Pistons
« Reply #49 on: February 28, 2016, 10:41:34 AM »
I cannot see it reducing comp that much to be worried about,if you are getting your head surfaced as part of the build,it will make up for a little,and new bores with fresh pistons are going to bring your numbers up to as new specs,so don't overthink it too much.billp
1978 CB 750K ard and webers
another anfob