Topic: Opening an engine, what should I check/replace/look for?

[ncstatecamp]

Ive just "finished" my lil 5000 mile jaunt around the eastern seaboard on my 750k2 and I have an oil leak. Its more then likely the pucks that go over the studs below the rockers, but while I have the engine out and the cover off what else should I change/measure/look at/service? I know the old saying is if its not broken dont fix it, but theres something to be said about preventative work too.

this is my first time diving into an engine, but Ive rebuilt the rest of the bike so I'm fairly certain I can handle it. Yes I do have the manual as well, though I can't always follow it very well.

Things I think I should check/change but tell me if Im wrong.

Cam chain - not sure how to check - anybody got suggestions?
cam chain tensioner - more then likely replace
piston heads- at least clean, not sure how to check
rings - more then likely replace?
gaskets - im assuming pretty much all have to be replaced (base, head, cover, any more?)
stud pucks - replace all?
valves - not sure...
valve springs - I can just measure I believe?
cylinder walls - measure but not sure what to do

any more suggestions on things to check?

I wasnt planning on ordering parts til I get it open and know what I need

what are the little white rings between the fins on the front? a couple have expanded due to oil saturation, not sure what they do...

as Ive mentioned it a 72 cb750. I received the bike as rolling frame and engine, which Ive spent the last 1.5 yrs restomoding. Previous milage unknown, except the 5k I put on it - which besides the leak ran like a champ. The previous pressure test ran 120 psi across the board but I'll be doing another before I crack it open. I do not wish to split the case.

[cakey]

I have just about putting my K1 engine back together but it was seized and not running. My list included:

Rebored .50 oversize
.50 oversize new pistons ( I did this to guarantee roundness of cylinders)
New valves (had these cut into the head)
11 helicoils on the head
Head re surfaced
New heavy duty cylinder studs
New primary chains
New primary chain tensioner and rubber
New cam chain
New cam chain tensioner and rubber
New transmission bearings set (7 I think)
New transmission springs (return springs etc)
New con rod bearings
New mains bearings
All new oil seals including oil pump
New locating dowels
New knock pins
Mew cover screws
New gaskets and o rings
Bead blasted heads and barrels


More than likely other stuff I have forgotten.

[ncstatecamp]

Luckily mine isn't seized so the bearings and anything below the shouldn't be necessary. Did you all of that bc it was needed or you thought might as well? Where did you end up purchasing stuff? When is an over bore needed?

[Jayelwin]

Replying to tag myself as a participant as this is a future question of mine.

[bjatwood]

If the compression is still good I wouldn't go any deeper than the head pucks. You say it's is running well right? 5K is a pretty good shake down test for a 41 Y.O. motor IMO Did yhe bike use much oil in the 5K?
If it aint broke don't "fix" it!

[ncstatecamp]

The oil it used was from it leaking out of the vents near the exhaust, never smelled like oil, though I'd get a bit of white out the tail pipe when it started up cold, and I believe the compression has gone down a bit as its a true #$%* to start cold.

Even if I don't go further then the pucks the info would be good.

[cakey]

Luckily mine isn't seized so the bearings and anything below the shouldn't be necessary. Did you all of that bc it was needed or you thought might as well? Where did you end up purchasing stuff? When is an over bore needed?

I am only an enthusiast when it comes to rebuilding so in saying that I have an opinion that if you are going to the trouble of splitting the cases then you should replace all internal rubber parts and orings as they get old and brittle so this is a must.

If there was any doubt about the bearings then it would be worth replacing ( if they are scratched up or any copper showing) this did not have anything to do with seizing just age and wear and tear.

I replaced all the transmission bearings because in my research I had read that they can go and the final drive bearing was susseptable to wear.

I had pitting in cylinder one where the rings had sat and rusted so getting it bored oversize was best option.

If I was going to only put new rings in then I would get it measured by a professional first to see if all cylinders were round. After getting them measured I would then decide which way to go.

I replaced valves because mine were crap.

I replaced with heavy duti cylinder studs because of the research I had done indicated it would assist with getting rid of oil leaks on the future.

I got the head re surfaced because a professional measured and set it had a low spot.

Helicoiling the threads in the head is a pretty common problem I think.

I replaced transmission springs because it made the world of difference to gear changing on my GL1000.

Open it up, check all measurements to specs in the manual and go with your gut.

I also really enjoy working on the engine and bike, it's my hobby so having it off the road is not an issue I have other bikes to ride. Even if it wasn't broke I would still do it because I enjoy it.

My stuff was purchased between

eBay
David Silvers
CSMNL
Honda shop
And other CB experts here in Australie

[Kickstart]

I think it really depends what your goal is.

I'm pretty much doing the same thing as Cakey, but my goal is two-fold:
1. I want to restore my engine to original "like new" performance (well, actually better than like new)
2. I want the learning experience of doing a complete rebuild.

But 1 & 2 come at a pretty hefty price, and admittedly it's really overkill for a bike that I will probably only take on 1 or 2 long rides per year (in addition to many shorty rides).

I recommend you purchase Hondaman's book "My CB750 book" if you haven't already.  It contains excellent set-by-step instructions for the tear-down, inspection, and re-assembly.  It also has explanations on certain service limits (i.e. acceptable levels of wear based on planned riding style an/or when should you replace/machine something).

Good luck!

Word of warning...  I didn't plan to replace so many things on my bike when I first started, but the temptation to make it perfect while you've got the engine open (i.e. "well I might as well get the crank balanced while I'm in here") is hard to resist... at least it is for me

[ncstatecamp]

Well I did a compression test and I'm pretty much 90's across the board. So definitely rings and at least lapping valves. The one thing I'm truely worried about in all this is the reassembly with correct timing. Can somebody give me a step by step on that?

[Don R]

On these small cylinder engines the volume of the tube on a tester can greatly affect the numbers. Low even numbers aren't neccessarily an indicator of a problem. Equal numbers are good.  Did you have the throttle open while testing?

[flybox1]

I'm doing this now...if it aint broke, dont open it!!!! 
bought my engine in pieces, so its going back together with bullet proof reliability in mind.

BUT, if you open the lower cases, and this is just for the bottom end....be prepared to write an $800 +/- check for:
HondaMans book - $80 +/-
crank and rod bearings $200
oil seals and various OEM o-rings needing replacement $60
HD primary and cam chains $150
rollers/tensioners for said chains $180
complete gasket kit $100
HD studs $80
roller Bearings (yamiya) - $?  (mine were good)
solvents, cleaners, paints,  tools (to do this all yourself)  $100
time -  lots

[ncstatecamp]

On these small cylinder engines the volume of the tube on a tester can greatly affect the numbers. Low even numbers aren't neccessarily an indicator of a problem. Equal numbers are good.  Did you have the throttle open while testing?

I did not have the throttle open but ran the test several times. Before my trip I was running 120's across the board. The bike now takes quite a few cycles to start when before it started up like a champ. I have to open it just to replace the stud covers anyway.

[ncstatecamp]

I'm doing this now...if it aint broke, dont open it!!!! 
bought my engine in pieces, so its going back together with bullet proof reliability in mind.

BUT, if you open the lower cases, and this is just for the bottom end....be prepared to write an $800 +/- check for:
HondaMans book - $80 +/-
crank and rod bearings $200
oil seals and various OEM o-rings needing replacement $60
HD primary and cam chains $150
rollers/tensioners for said chains $180
complete gasket kit $100
HD studs $80
roller Bearings (yamiya) - $?  (mine were good)
solvents, cleaners, paints,  tools (to do this all yourself)  $100
time -  lots

Yeah no way am I cracking open the bottom end, no need too.

[Vinhead1957]

When you open it up look for damage and condition it will guide you.  Check tolerances before replacing things.  The condition of the valves will indicate if a valve job is needed.  Exhaust valves will be lighter grey than intakes. Check intakes and exhaust for the condition of the seals. Some carbon is ok. But wet carbon around the seats is clue of leaky seals. 

[ncstatecamp]

When you open it up look for damage and condition it will guide you.  Check tolerances before replacing things.  The condition of the valves will indicate if a valve job is needed.  Exhaust valves will be lighter grey than intakes. Check intakes and exhaust for the condition of the seals. Some carbon is ok. But wet carbon around the seats is clue of leaky seals.

I've started to make a list of things to check and their service limits: valve guide, valve springs, rings, ring seats, going to get the cylinders measured, cam chain, cam chain tensioner. Anything else?

[flybox1]

add guide seals and HD studs to your list.

[ncstatecamp]

add guide seals and HD studs to your list.

Uhh, not sure what those are....

[cakey]

The studs are the long rods that hold your barrels and heads down on the case. The HD studs are thicker in the shaft than the originals.

The valve seals are the rubber seals that are under your valve springs and go over your valve guides

[ncstatecamp]

I knew what studs were just wasn't sure what hd studs were. So those should be replaced? How often?

[ncstatecamp]

I guess I'll see the valve seals when I take it all apart. So check those or just straight up replace?

[cakey]

Always straight up replace the valve seals. They normally come in gasket kits or are not too much to buy anyway, but don't waste time checking them just replace.

HD studs are a debatable subject of wether to use or not use. I used them but plenty of people don't. Do some research on the forum and get some different opinions.

[ncstatecamp]

Sounds good. Any brand of gasket I should absolutely stay away from?

[cakey]

Nah sorry dont know the answer to that.  I use a mixture of OEM stuff and a Vesrah kit. I have never had problems with Vesrah but it's a lot more affordable to use where. I live than OEM.

[flybox1]

your first choice for gaskets, seals, and orings should be OEM.
if no, then go for good, known kits, like the ones by vesrah or athena, or the one by cyclex
each of the kits has been know to lack something, either a specific item, or an item that just isnt up to snuff for our applications.

plenty of threads out there on this...

[Don R]

If I didn't replace the studs,w/ Heavy Duty, I'd use MLS (multi layer steel) gaskets on the head and cylinder so you don't need to retorque. I did both. In my case I opened a 14,000 mile engine just for nickel washers and ended up going with a port job, 836 kit and a cam and spring kit. But that's just how I roll. HA! It goes like stink now!