Head Job

[1980cb650]

Well on my last ride the bike turned over 13,000 miles and started leaking oil all over my left foot pretty bad. It had already leaked a little from the head cover, but this new leak is pretty bad. I haven't really checked it out yet but I think it's coming from the head gasket. Is doing a head gasket and all the upper engine stuff a pretty easy job? Anything else I should do while I have it off? Or should I just let it go and try to sell it. I just bought a house so I'm on a really limited budget now.

[Ibsen]

yes, replacing the head gasket is a pretty easy job. You will need a top end gasket kit though, since you should replace all the o-rings and rubber gaskets for the cylinder head and rocker arm cover at the same time.

[DammitDan]

You can buy a top end kit from a lot of online sources (although a lot of them seem to be out of stock for the CB650 right now...) They range from $85 to $125.

Here
or Here
or here
Or here...

[Volker_P]

You can do that job with the engine in the frame so the effort is quite limited. That leak is a typical feature of the CB650, I did work on that 3 or 4 times the last 14 years.
Basically it is only the two 5x2.5mm O-Rings that you have to change so if you work clean and you have a suitable high temperature grease and know how to use it you may also reuse the head gasket if you manage to get it off in one piece.
On the bottom of the cylinder, there are also two 10x2.5mm O-Rings but change them only if required. The reason is that the original (black) main bottom gasket may be a horrible thing to get off, a very time consuming job.
Clean the engine with high pressure cleaner especially at the cylinder head screws which are hard to access in the center front. It is hard to get the mud out of there by hand, but important to get the screws out without damage.
If mud falls in the cylinder screw threads, get it out (e.g. with the help of a long drill). Cylinder head screws should run in about 13 turns easily when the threads are intact and clean, you may use one of the two longer ones in the rear center without washers to check all.
Use a small torque wrench for the cylinder head cover bolts, the threads are very suscreptible. Usually you can reuse the large O-ring gasket there, but clean everything carefully and turn the 22 screws stepwise in the given pattern. This is more effective (and 8-10Nm should be enough) and less dangerous than enhancing the torque to get it tight.
Getting the carbs out may be difficult, plan some time for that. Sometimes it is helpful to remove two carb boots on the left side.
Avoid to remove the camshaft tensioner (just loosen it if required) as it is a bit tricky to get it in again in correct position.

Well, that's what I remember for now, I wrote down my last cylinder head action here:
http://www.hondacb650.com/viewtopic.php?t=52
It's a bit lengthy, but maybe there are some useful hints for someone who tries it for the first time.

Maybe it is also a good idea to try to smoothen the seats of the O-Rings (I remember some traces from machining)
to stretch the change interval. I kept this for the next time.

Good luck!

[1980cb650]

I think I'm going to order this engine gasket kit from Parts N More.
https://www.partsnmore.com/cat_index.ph ... ory=engine
Has anyone had good experiences with them? They're shopping cart says that they are in stock. I want to make sure someone has had good experiences with this company before I order from them.

-Andy

[DammitDan]

I've ordered from Parts n More before, and they're good quality (except the tappet adjustors!)

The Head kit is from Athena, which worked well for me.

[Vatch]

Volker, DD, or Andy, or anyone else that has done the head job,

How long does the head job take for a virgin? I have removed the carbs and have an estimate of the time for that job. If I am going to keep the 650 running I need to do the head job, but with a 1 year old daugher and other obligations, I need to plan time use carefully. I don't want to get started and not be able to finish the job for a month I've been meaing to get to this for months now. Such may be the life of a new father.

Cheers,
-Jeff

[Volker_P]

Such may be the life of a new father.

Congratulations!

If everything just works and carbs are already off, I guess can be done in one day (6-8h) if you work carefully and straightforward.

However there are some points that may cause extra time where preparation/cleaning has much potential to save this.
Especially cleaning the inner head bolts or their threads may take hours (and there is always sand and small stones in the corners of the cylinder head) so I recommend to use a high pressure cleaner there before opening anything. When sand/stones fall down into the threads (and it does), failure of them is almost sure (you need at least 13 turns free depth AFAIR). It is worth to check free running of the threads with one of the two long rear center bolts (with the washer removed) before reassembly. Another thing is the head cover. You should take the time to loosen and tighten all the 22 bolts in about 5 steps with a small enough torque wrench and place it on a perfectly flat board and make sure you don't mix up the bolts.
Similar with the head bolts. You need a slim enough 12mm socket spanner to access the inner head bolts. Make sure that it sits perfectly down (stones/sand!) before you try to turn a bolt. With the head of the bolt damaged, the options not to have to drill it out go poor.
It is also worth spending time on cleaning the surfaces and avoid any bending of head and head cover. I would guess this is even more important than using new gaskets. It also makes sure that you get it tight at the given torques. You should not exceed them neither at head nor at head cover bolts as there is not much reserve. In this sense a small enough torque wrench is the most urgent tool for this job.

So what I want to say ist that this job is not really heavy or time consuming but provides some traps that may cause further damage and additional excessive work or even the help of a workshop. Spending time on preparation and on intensive cleaning of everything is definitively worth it, and the time required for this may exceed the pure bolt turning work time considerably. This must not irritate you at all! The 5x2.5mm O-Rings are the decisive parts to get it oil tight, so if you can get it, use nitrile rubber (as provided by the David Silver gasket set which was recommended by Ibsen) or Viton (to borrow from your local employers workshop. )
Good luck!

[pae]

Hi Volker, this is so useful, thanks for taking the time to share your experiences. Now I've got all the parts cleaned/plated/painted my current task is getting the rolling frame back together. As soon as that's done I'll start on the engine and repalce the head gasket, so I'll soon be printing this off and sitting down alongside the engine to rehearse it in my mind before I start unbolting.

I was thinking of pulling the head off whilst the engine is on the bench, then putting the engine back in the frame. That way, I guess, I'll have a reasonably good amount of clearance to get it in without damaging the freshly painted frame. Then re-fit the head in the bike. Do you think that is sensible?

I've not checked, but I guess from what you say that by removing the head you don't disturb the cylinder base gasket at all? Is the cylinder block torqued down by separate or additional bolts? I hope so as I have no need to strip it down that far.

thanks, Phil

[Volker_P]

Good to hear that one can use that info. I also encourage to use the search function as there are other useful descriptions in this board, even with pictures.
Leave alone the base gasket if you can, especially if it is still the original black, stubborn one. It probably will partly split when you try to lift the cylinders and it was really hard to remove (I spent hours). I never want to do that again.
The cylinder bolts also hold the cylinder block, there are no additional small bolts or so to fix it. If you do not want to remove the cylinders but like to put the engine in the frame like that, you may fix it again with the head bolts using some nuts as spacers or using shorter 10mm bolts. On the cylinder bank I would use the old head gasket and a cut out part of carton for protection of the head surface and to close the openings (pistons and oil lines) during mounting.
Don't get the cam chain tensioner out unneccessarily, there is a good chance to mount it wrongly again without even noticing it.
Getting the front cam chain guide out would require to get the cylinder bank lifted a bit, so just leave it in.
The most dangerous parts for your fresh painted frame are probably the exhaust bolts. They may break during removal efforts in case they are quite stuck so your planned proceeding without the head is probably the more safe one. Oil filter case may also be disturbing.

[pae]

Yes, the oil filter housing will be off when I refit. And there'll be plenty of pictures coming so I can hopefully add my thoughts to help to others in future.

regards, Phil

[Ibsen]

Pics will be great.

I have also posted a few pics in this topic:

viewtopic.php?t=74