Top end rebuild, my discoveries and disappointments

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Surfdad
Posts: 4
Joined: Thu Feb 02, 2017 4:36 pm

Top end rebuild, my discoveries and disappointments

Postby Surfdad » Sun Dec 16, 2018 8:36 pm

I just finished a top end rebuild of by 1982 CB650SC and wanted to share some things I discovered, was worried about and disappointments.

The first thing I found was decent oversize pistons:

https://www.cruzinimage.net/?s=cb650+pistons

Original, .5 and 1.0 mm over. Good quality with fast shipping. Do allow 10 days for USPS to deliver to your door once thru customs.

46961245_2040267096030945_1365556663892836352_n.jpg
46961245_2040267096030945_1365556663892836352_n.jpg (56.87 KiB) Viewed 1219 times


I read so much about the cam chain tensioner missing the lower slot. I even watched YouTube videos of folks having trouble. I was freaking
out! If you follow the technical guide, you're golden. BEFORE sliding the cylinders over the first set of pistons, make sure the cam chain
tensioner is installed into the cylinders finger tight. It slid right in for me.

I read a lot of confusing inormation about aligning the index mark on the cam. That index mark is 1/4" wide. It should point forward towards the exhaust and the MIDDLE of the Index mark aligns with the surface of the head. Not the top or bottom of the index mark with the head surface. Basically the top of the index mark will be parallel with the head surface and about 1/8" above it.

While I had my head and head cover off, I polished the head cover and also removed the tach drive. The CB550 tach drive block offs work perfectly, but of course you have to completely remove the tach drive. I saw several, and bought one that was polished aluminum like my head cover.

44951244_2001472429910412_5091243546799767552_n.jpg
44951244_2001472429910412_5091243546799767552_n.jpg (44.63 KiB) Viewed 1219 times


http://www.fastfromthepast.com/dtdbop-cb5c

I purchased a top end gasket set off ebay, but it seems to be offered on many of the parts houses. Here is a link to one at 4into1.com

https://4into1.com/top-end-gasket-set-h ... 1978-1982/

honda-cb650-top-end-gasket-set-SP09-2700__68569.1527013621.1280.1280.jpg
honda-cb650-top-end-gasket-set-SP09-2700__68569.1527013621.1280.1280.jpg (556.69 KiB) Viewed 1219 times


It's good quality, but it doesn't include the two 11 x 2.5 mm o-rings that go around the oil delivery channels. It has the base gasket, just not the o-rings. You can still source them at Bike Bandit, etc. but that's pricey and irritating! The full gasket set, however, does include those o-rings.

That's my 2 cents for anyone undertaking this same task.

User avatar
GeorgeSweety
Posts: 391
Joined: Tue Aug 08, 2017 11:47 am
Location: UK.

Re: Top end rebuild, my discoveries and disappointments

Postby GeorgeSweety » Thu Dec 20, 2018 2:51 am

Hi Surfdad, how did that head gasket work out for you? I bought an NE gasket set for my 82 SOHC CB650SC Nighthawk but the head gasket was wrong, the cam chain tunnel cut out was a different shape, the cylinder holes and front bolt holes didn't line up.
In the pic below the top gasket is a genuine Honda gasket and the bottom gasket is from the NE set which looks identical to the one in your kit.

head gasket difference.jpg
head gasket difference.jpg (129.58 KiB) Viewed 1194 times

Surfdad
Posts: 4
Joined: Thu Feb 02, 2017 4:36 pm

Re: Top end rebuild, my discoveries and disappointments

Postby Surfdad » Sun Dec 23, 2018 9:08 am

That wasn’t my actual gasket set, just a depiction. My head gasket aligned fine. Perhaps they’ve fixed that problem? I’ve had no leaks and no shredded gasket material in my oil!

Surfdad
Posts: 4
Joined: Thu Feb 02, 2017 4:36 pm

Re: Top end rebuild, my discoveries and disappointments

Postby Surfdad » Mon Dec 24, 2018 9:42 pm

GeorgeSweety,

I didn't take any pictures of my head gasket installed, but I did take a picture of the bottom of my head after I finished the valve job. The bottom of the head is basically a rectangle around the cam chain opening. See below. I'm not sure, but that weird gasket you got would seal when flipped over, right? It looks to my bifocals, that the basic rectangle would be covered and the pivot for the front cam chain guide is effectively covered by the head, so maybe the lack of cut out is inconsequential? The weird indent, when flipped, I think doesn't impact the seal nor get in the way of the cam chain. I could be wrong, but it looks like it would work flipped over.

45098227_2005052169552438_8671273996911640576_n.jpg
45098227_2005052169552438_8671273996911640576_n.jpg (38.13 KiB) Viewed 1147 times

User avatar
GeorgeSweety
Posts: 391
Joined: Tue Aug 08, 2017 11:47 am
Location: UK.

Re: Top end rebuild, my discoveries and disappointments

Postby GeorgeSweety » Wed Dec 26, 2018 8:48 am

Surfdad wrote:GeorgeSweety,

I didn't take any pictures of my head gasket installed, but I did take a picture of the bottom of my head after I finished the valve job. The bottom of the head is basically a rectangle around the cam chain opening. See below. I'm not sure, but that weird gasket you got would seal when flipped over, right? It looks to my bifocals, that the basic rectangle would be covered and the pivot for the front cam chain guide is effectively covered by the head, so maybe the lack of cut out is inconsequential? The weird indent, when flipped, I think doesn't impact the seal nor get in the way of the cam chain. I could be wrong, but it looks like it would work flipped over.

45098227_2005052169552438_8671273996911640576_n.jpg


Nope! It wouldn't work flipped over, I tried before I had to hunt down an original Honda gasket.

Dustin
Posts: 15
Joined: Sat Mar 22, 2014 5:51 pm

Re: RE: Top end rebuild, my discoveries and disappointments

Postby Dustin » Sun Apr 14, 2019 11:10 am

Surfdad wrote:I just finished a top end rebuild of by 1982 CB650SC and wanted to share some things I discovered, was worried about and disappointments.

The first thing I found was decent oversize pistons:

https://www.cruzinimage.net/?s=cb650+pistons

Original, .5 and 1.0 mm over. Good quality with fast shipping. Do allow 10 days for USPS to deliver to your door once thru customs.

46961245_2040267096030945_1365556663892836352_n.jpg


I read so much about the cam chain tensioner missing the lower slot. I even watched YouTube videos of folks having trouble. I was freaking
out! If you follow the technical guide, you're golden. BEFORE sliding the cylinders over the first set of pistons, make sure the cam chain
tensioner is installed into the cylinders finger tight. It slid right in for me.

I read a lot of confusing inormation about aligning the index mark on the cam. That index mark is 1/4" wide. It should point forward towards the exhaust and the MIDDLE of the Index mark aligns with the surface of the head. Not the top or bottom of the index mark with the head surface. Basically the top of the index mark will be parallel with the head surface and about 1/8" above it.

While I had my head and head cover off, I polished the head cover and also removed the tach drive. The CB550 tach drive block offs work perfectly, but of course you have to completely remove the tach drive. I saw several, and bought one that was polished aluminum like my head cover.

44951244_2001472429910412_5091243546799767552_n.jpg


http://www.fastfromthepast.com/dtdbop-cb5c

I purchased a top end gasket set off ebay, but it seems to be offered on many of the parts houses. Here is a link to one at 4into1.com

https://4into1.com/top-end-gasket-set-h ... 1978-1982/

honda-cb650-top-end-gasket-set-SP09-2700__68569.1527013621.1280.1280.jpg


It's good quality, but it doesn't include the two 11 x 2.5 mm o-rings that go around the oil delivery channels. It has the base gasket, just not the o-rings. You can still source them at Bike Bandit, etc. but that's pricey and irritating! The full gasket set, however, does include those o-rings.

That's my 2 cents for anyone undertaking this same task.
Hey Surf,

I am a total newb getting into this. My 1982 cb650 is apart right now and I'm reading yo refurb the engine.

I am not entirely sure of what I need to order before I start the project. Would appreciate your help.

I know u meantioned one kit not having a couple of parts. I'd like to order everything before I get started. Which kit is it I should order? I am guessing this one?
https://4into1.com/engine-gasket-set-ho ... 1979-1982/

I don't know where to get piston rings or if I should replace the Pistons. I'm kind of lost.

Dustin.

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