Front Fork Strip

[mcconnellfrance]

Hi all, I have started to overhaul my front forks on my 1964(5) CB77 Frame/No 401130. I was not impressed by the damping on the front suspension which seemed very poor compared with my memory of the CB72 I owned in 1969. (Maybe my memory has improved the CB72 over time!).

I started the strip down today having loosened the fork seal housing with a strap wrench before removing the forks from the bike. These loosened quite easily which I was not expecting.

https://www.flickr.com/photos/131927779 ... res/9X2T7j

Then I ran into the well known problem on this forum. The lower case has been distorted by someone installing a too long bolt to attach the mud guard. Perhaps rather brutally, I used a piece of wood and a mallet to remove the lower case. Both the forks have this problem.

https://www.flickr.com/photos/131927779 ... res/U2B87g

I was expecting to find that the Fork piston was staked onto the fork pipe but surprisingly the fork pipe is a later part number with the piston fixed by the snap ring. Looking at the parts book, this configuration was used with the later alloy lower case.

https://www.flickr.com/photos/131927779 ... res/T23ZXS

Examining the pistons, it is clear that the distortion on the lower case has damaged the pistons, one of them being clearly distorted.

https://www.flickr.com/photos/131927779 ... res/680k6y

I have not had a chance yet to really assess the distortion in the lower case but it was sufficient to make the withdrawal of the fork pipe very difficult.

https://www.flickr.com/photos/131927779 ... res/p07s58

I then had a try at removing the fork seals from the fork seal housing. The spring clips which locate in the internal groove came out easily enough. I have not posted a photo but the seals are stuck very firmly in the housing despite trying to use a screwdriver and mallet to hammer out the seal outer ring. They appear to have been installed aith a black sealant. I saw a post from LM which advises that he uses a 1/8 inch chisel to remove these seals. After having a good whack at them, I am concerned not to distort the housing so I gave up tonight.

So my questions for the learned members of this great forum are:

1. Is there any problem to combine the later fork pipe configuration with the earlier steel lower case?

2. Would the distorted lower case and piston cause a oil leakage past the piston resulting in the poor damping that I experienced?

3. Is there a way to correct the distortion in the lower case?

4. Any means to support the seal housing while trying to chisel out the seal?

Thanks in anticipation of your advice.

[PhilD]

Hi, re. Q4 regarding removal of fork seals I too have had great difficulty in removing these from the seal holders after 30 plus years of standing in a garage. If you intend to rechrome the holder then you can apply heat from a propane or MAP torch to expand the holder and melt the outer part of the seal to free it. If that doesn't work then you can carefully cut through the metal part of the seal with a rotary cutter to release it. You need to be careful if you just try to remove the seal with a chisel and brute force as it is very easy to damage the fork holder as I've done that myself and replacements aren't easy to find. Sorry I can't help with your other queries as fortunately I've not encountered the problem of too long bolts damaging the forks.
PhilD

[mcconnellfrance]

Phild,

Thank you for the advice on the seal removal. I want to avoid damaging the seal holders so heating seems the best option even if I have to rechrome afterwards. I will perhaps have a go with the Dremel to try to cut the metal part of the seal, taking care not to cut into the seal holder. If that is too difficult, heating is the next step.

Thanks again.

[PhilD]

I've found that fitting the new seals can also be tricky as they are a tight fit and it's easy to get them at a slight angle so that they jam and then you end up damaging them to get them out to try again. I now cool the new seals overnight in a domestic freezer, warm up the fork seal holders with a hot air gun, apply some lubrication and after carefully lining up the seal pull it into place with a bearing puller (threaded bar with suitably sized washers). Hope this is useful.
PhilD

[G-Man]

Gordon

There are 'very' early and early type of fork tubes for the bikes with steel lowers. Only the fatter (38mm) type had the riveted lower bush. Later steel types had the snap ring.

The distortion should be just limited to the inside of the slider next to the fender bolts. I managed to get a small grinder in the gap and remove some of the 'pip' on some sliders I had a problem with.

G

Hi all, I have started to overhaul my front forks on my 1964(5) CB77 Frame/No 401130. I was not impressed by the damping on the front suspension which seemed very poor compared with my memory of the CB72 I owned in 1969. (Maybe my memory has improved the CB72 over time!).

I started the strip down today having loosened the fork seal housing with a strap wrench before removing the forks from the bike. These loosened quite easily which I was not expecting.

https://www.flickr.com/photos/131927779 ... res/9X2T7j

Then I ran into the well known problem on this forum. The lower case has been distorted by someone installing a too long bolt to attach the mud guard. Perhaps rather brutally, I used a piece of wood and a mallet to remove the lower case. Both the forks have this problem.

https://www.flickr.com/photos/131927779 ... res/U2B87g

I was expecting to find that the Fork piston was staked onto the fork pipe but surprisingly the fork pipe is a later part number with the piston fixed by the snap ring. Looking at the parts book, this configuration was used with the later alloy lower case.

https://www.flickr.com/photos/131927779 ... res/T23ZXS

Examining the pistons, it is clear that the distortion on the lower case has damaged the pistons, one of them being clearly distorted.

https://www.flickr.com/photos/131927779 ... res/680k6y

I have not had a chance yet to really assess the distortion in the lower case but it was sufficient to make the withdrawal of the fork pipe very difficult.

https://www.flickr.com/photos/131927779 ... res/p07s58

I then had a try at removing the fork seals from the fork seal housing. The spring clips which locate in the internal groove came out easily enough. I have not posted a photo but the seals are stuck very firmly in the housing despite trying to use a screwdriver and mallet to hammer out the seal outer ring. They appear to have been installed aith a black sealant. I saw a post from LM which advises that he uses a 1/8 inch chisel to remove these seals. After having a good whack at them, I am concerned not to distort the housing so I gave up tonight.

So my questions for the learned members of this great forum are:

1. Is there any problem to combine the later fork pipe configuration with the earlier steel lower case?

2. Would the distorted lower case and piston cause a oil leakage past the piston resulting in the poor damping that I experienced?

3. Is there a way to correct the distortion in the lower case?

4. Any means to support the seal housing while trying to chisel out the seal?

Thanks in anticipation of your advice.

[mcconnellfrance]

Graham, Thanks for the good advice as usual! I was thinking of getting a broach made up to the inside diameter of the lower case and trying to restore the internal shape. I don't have a grinding tool with that sort of reach. Was it a special tool you made up?
Regards,
Gordon

[mcconnellfrance]

PhilD,
Still not got the old seals out yet. Going to try again tomorrow. Your process for the seal replacement looks good and I will adhere to it when the time comes. My major issue is how the get the lower case back in shape. Graham has done it by grinding so it is possible to recover them which is a relief! Thanks again for your kind advice.
Regards,
Gordon