4 Stroke Top end rebuild

[smegballs]

My mate has a superdream that is burning oil, not too much but it is noticeable - especially up hills. We were perhaps thinking of giving it a bit of TLC but not too much as it is old and pretty wanked.

We was thinking of having the head off and cleaning it up, lapping in the valves, new valve stem seals, and a hone and re-ring.

I've done valves before so I know whats going on there but I'm not sure whats the deal with the bore. If its gets measured and the pistons/bore is wanked then will a hone and re-ring make much difference? Or would it definately need a rebore? The bike is pretty old as it is so its not worth spending the money on rebores and pistons, but 40 quid of rings and seals might make it a bit better (and its something to do over xmas break).


Is it worth bothering with or will it just open a nice big can of worms?

[hmmmnz]

well if you don't mind taking the head off to do the valve seats ect,
then you may as well do the rings, they wear quicker than the barrel... usually
____________________
the humans are dead
I kick arse for the lord
Wiring Diagrams BIDNIP it bitches

[smegballs]

Yeah I know on lots of four strokes just re-ringing gives a nice compression boost on a tired engine.

Only thing I'm wary of is it being taken apart and then not functioning once its all back together. I think I'll comp test it to get an idea wether its valves or rings that are leaking.

[unitybiker]

if the compression test says knacked then just put some molyslip or slick 50 in it and thrash it till it starts smoking .


or , if you are going through all that trouble on the head then why not bung a couple of new pistons in it as well ,



it's not my money and time being spent but for a few dollars more?

[smegballs]

Well I've priced up a set of rings for about a tenner each and piston kits are like 40 each.

So while 20 quid on rings isnt that bad, 80 quid with new pistons is 4 times as much and probably more than its worth. Certainly more than my mate will want to spend.

[unitybiker]

yup you 're right u could get a sechand engine for that ,If it;s a nice bike it can be worth cleaning and spraying engine and doing a bit of nimor paint work on the inaccessable bits of the frame

[.Chris.]

Depends what the bores are like (which obviously you're not going to know until you take the head off). If the bores are badly worn then putting new rings on might work in the short term but probably won't last very long, so you may as well go for a rebore and new pistons. If the bores are OK then new rings would be fine.

A secondhand engine is an option, but a bit of a gamble - it could be equally as knackered or have other issues.
____________________
Chris
1985 Kawasaki Z550F

[Vincent]

Best way to find out if it needs a rebore is to buy a new set of rings, place the top one inside the bore and use the original piston to push it in square. Measure the end gap on the ring about 1/4 down from the top of the cylinder and again about 2/3ds down. Then consult your workshop manual, (I'm sure you have one), for the tollerances. There are Bore Guages but I've found them to be pretty useless.
Check for marks on the piston crown to see if and by how much, the cylinders have been rebored before.