Topic: '77 CB750 K7 Pistons

[Bl4ckC4t]

Does anyone have any idea where to source pistons for the K7? The one I am buying is seized and I am gathering prices for all the potential needed parts to get it running. However, I am having trouble finding pistons that match OEM for the '77. Any help would be appreciated.

[robvangulik]

What sources did you try, before asking?
Www.cmsnl.com....

[Bl4ckC4t]

Vintagecb750, and similar sites, including the one you listed.

No one seems to have any actual pistons at standard size for the 1977.

Pretty much everyone ends at 76, and under my understanding, 76 and 77 have different sizes due to the compression ratio.

[Airborne 82nd]

Does anyone have any idea where to source pistons for the K7? The one I am buying is seized and I am gathering prices for all the potential needed parts to get it running. However, I am having trouble finding pistons that match OEM for the '77. Any help would be appreciated.

If I'm reading this right it sounds like you have not broken the engine down yet. Don't waste time you may not need them in fact you may not need anything. It could be a boat anchor. I hope not. But if it is seized I would take it apart far enough to see why it is stuck. Then you can make a better list.
 

[Bl4ckC4t]

You are correct, I have not tore it down yet. I am actually waiting on the owner to have title in hand. However, I am only looking in the event that I have to swap pistons. I know the cause of the sieze, but not the extent. It was left outside for a period of time without spark plugs in the rain. While I am hopeful for an easy recovery, I just want to plan for the worst and hope for the best.

[Airborne 82nd]

I would pull the pan to see how bad the water damage is at the bottom end that would concern me more than the top depending how long water has been in it. I don't know why someone does that Good Luck

[PeWe]

Head will most likely need to be refurbished. All seats to be cut. Exhaust valves with guides might need to replaced.

[Bl4ckC4t]

Thanks lieutenant. I will keep that in mind, and thank you for your service. Also thank you for the hard work you put into that batt.

[Bl4ckC4t]

Head will most likely need to be refurbished. All seats to be cut. Exhaust valves with guides might need to replaced.

Had this feeling, but I really hope that it isn't going to be too much more than this.

[PeWe]

Take it apart before deciding. Bores might be damaged, bigger pistons to be used. Or it might have bigger bores than stock.

If OK and bike to be stock.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F132002710167

[Bl4ckC4t]

Take it apart before deciding. Bores might be damaged, bigger pistons to be used. Or it might have bigger bores than stock.

If OK and bike to be stock.
https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F132002710167

I will keep that in mind. However, those are .5 over, would that be a problem?

[bryanj]

If the pistons are stuck chances are it will need aeebore anyway.

[Bl4ckC4t]

Good point. Thank you!

[PeWe]

Fresh bore, new pistons with correct clearance and ring gaps plus a refurbished head will make  good.
Inspect status first. When at it replace both chain tensioners that probably are hard and have left rubber parts in oil pan.

These old engines need some new parts due to age, not only usage. Good idea to read Hondaman's CB750 book before

[Bl4ckC4t]

Fresh bore, new pistons with correct clearance and ring gaps plus a refurbished head will make  good.
Inspect status first. When at it replace both chain tensioners that probably are hard and have left rubber parts in oil pan.

These old engines need some new parts due to age, not only usage. Good idea to read Hondaman's CB750 book before

Talking about this one? ttps://www.amazon.com/CB750-book-Putting-Them-Back/dp/0557310237/ref=asc_df_0557310237/?tag=hyprod-20&linkCode=df0&hvadid=317002210742&hvpos=1o1&hvnetw=g&hvrand=6498158319411224404&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9024228&hvtargid=pla-624928938144&psc=1

[PeWe]

Fresh bore, new pistons with correct clearance and ring gaps plus a refurbished head will make  good.
Inspect status first. When at it replace both chain tensioners that probably are hard and have left rubber parts in oil pan.

These old engines need some new parts due to age, not only usage. Good idea to read Hondaman's CB750 book before

Talking about this one? ttps://www.amazon.com/CB750-book-Putting-Them-Back/dp/0557310237/ref=asc_df_0557310237/?tag=hyprod-20&linkCode=df0&hvadid=317002210742&hvpos=1o1&hvnetw=g&hvrand=6498158319411224404&hvpone=&hvptwo=&hvqmt=&hvdev=m&hvdvcmdl=&hvlocint=&hvlocphy=9024228&hvtargid=pla-624928938144&psc=1

Yes, look for the Hondaman book thread with link to how to purchase with coupon
http://forums.sohc4.net/index.php/topic,65293.425.html

[Bl4ckC4t]

Thank you PeWe