Advice on replacing gaskets

If it's broken or just needs tweaked

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jschuk
Posts: 2
Joined: Wed Aug 30, 2017 2:29 pm
Location: Denver/Littleton

Advice on replacing gaskets

Postby jschuk » Tue May 28, 2019 1:44 am

First post here. I have my father's 1981 CB650 standard (some of you have seen his pictures of the bike), and it leaks oil at the cylinder head and oil pan (not uncommon). I bought the full gasket kit from 4into1 and I plan on replacing most of the gaskets. My 1st question is should I replace the gasket for the cylinder block? It is not leaking there so I am leaning towards leaving it alone. My 2nd question is can I replace the oil pan gasket without removing the engine? I only looked down there long enough to see where the oil is leaking from, and not how accessible the bolts are. My last question is am I able to reuse the bolts/nuts/screws or are there other items that have to replaced? As a FYI the gaskets I received look to be D&K gaskets.
https://4into1.com/engine-gasket-set-ho ... 1979-1982/

This is my first motorcycle and I am eager to ride it, but I don't want to damage it. I consider myself mechanically inclined and am fairly certain that this job should be doable at home. I try to do my own maintenance, but besides routine maintenance I haven't done anything more serious than replace axles (bad CV joints) and removed valve covers and intake manifolds. I have the Cylmer manual, and I have been trying to read through the forums to educate myself so I don't ask silly questions.
Thank you,
Jason

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

Re: Advice on replacing gaskets

Postby GeorgeSweety » Tue May 28, 2019 2:01 pm

Hi, I personally would replace the cylinder base gasket because it may not leak now but when you undo the head bolts you may disturb it, imagine how you'd feel after doing the top end gaskets only to have the base gasket start blowing after you've finished the job. Another very important thing to remember is removal of the head bolts, over the years the head bolt tunnels will have filled up with an assortment of debris and road crap which can become baked solid, you will need to clean this out as much as humanly possible before you remove the bolts (should read damn near impossible with the engine in the frame :x ), when you remove the bolts this crap is gonna fall down into the head bolt threads, when you replace the bolts this crap is gonna do its very best to help you strip the head bolt threads.
The sump will come off with the engine in the frame, if you are gonna do the top end gaskets then you'll already have the exhausts off the bike which gives better access and a clearer view of what you are doing.
With the amount of work you are considering I would remove the engine, awkward but manageable, does the starter motor engage perfectly? If not I would consider removing the starter motor clutch through the sump and replacing the rollers, springs and caps while the engine is out if you do decide to remove it, for good measure I would also drill out and helicoil the head bolt threads as the original threads in the casings are usually on the verge of giving out if the top end has previously been off a few times. Long winded reply I know but I wanted to give you as much info as I can before you start. If you lived near me I'd come and give you a hand.

jschuk
Posts: 2
Joined: Wed Aug 30, 2017 2:29 pm
Location: Denver/Littleton

Re: Advice on replacing gaskets

Postby jschuk » Thu May 30, 2019 12:50 am

Thank you for the very quick reply. That makes sense about the cylinder gasket possibly losing its seal. I also appreciate the advice on cleaning the engine 1st. I might remove the engine after all. I could then tip it over to help prevent crud from falling in, plus it would make the oil pan even more accessible for cleaning. The bike has less than 9400 miles on it and has never been opened up. The starter sounds great. The bike actually starts and runs reasonably well, but it does need some carburetor tuning and possibly cleaning (that will be another thread). I just realized I should probably do a compression test before I open it up and then again after I put it together to make sure I didn't screw something up. Is there anything else I am missing?

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

Re: Advice on replacing gaskets

Postby GeorgeSweety » Thu May 30, 2019 2:36 am

The only thing I can think of before you start work is to get a piece of thick cardboard and draw a rough outline of your rocker box cover and punch holes through the card for each of the 22 bolts, the bolts are three or four different sizes and it will save you a lot of fiddling about on reassembly, slacken the bolts in sequence according to your manual and when they are all loose remove them one at a time and push them through the card in their correct location. ps. Take loads of pictures just in case you forget where something goes.........ask me how I know :oops:


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