Honda GB400: Replacing Cylinder, Piston, and Valve Seals

[mark247]

Ok so here is where im up to. I have got the head and bore off and have taken the piston out. Its wierd, i havent measured the rings or anything but the bore looks not bad at all and the piston looks alright too. Im guessing most of the oil is gettng through the valve seals at this point in time, i cant get the springs out here because i dont have a compressor, so im going to get the bike shop to do that. Looking at the valves from the bottom they look quite carboned up, and also the spark plug is shocking, and i cant get the spart plug out because none of our spark plug tools things fit in past the head to get to it, another job for the bike shop i guess..

I have had a few minor mishaps on the way, i missed one of the head bolts and was wondering why when i pulled on the head it wasnt coming off, but i finally found it RIGHT IN BY THE SPARK PLUG, bloody hard to get at but i go it. Oh and when i was unscrewing one of the bolts in the head i knocked a piece off the place where the camshaft bearings fit, but its very minor ( see the left point in the pic ) oh and there has been a bit of rubbing going on with the cam chain, i can see wear on the casting. But for all i know that happened a longggg time ago.

So where am i up to?

Well none of my stuff has come in the mail yet, so i need to wait for that, and i cant get the valve springs out. So next thing to do is get the stuff in the mail, take the head into the shop and get them to put the seals in for me, also get them to get the spark plug out ( i might just worry about that later )

I also need a torque wrench so i can put my new second hand bore back on.

The thing im most worried about is getting the camchain, tensioner and camshaft back on correctly, i really dont wanna stuff that up. But ill worry about that when i come to it.

[mark247]

Here are some more pics ( kinda useless ones )

[mark247]

Well sinse last time i posted about this the guy who was sending me the replacement piston and stuff finally looked at the piston he was gonna send me and found it had dents in the top of it ( probably not going to buy anything from them again ) , so i got my money back off him. I thought all was lost, but i found a really good piston and bore in Tauranga that i got cheap, the shop has just finished "refreshing" that which probably means a quick hone, and some other stuff. But the rings are all good so thats whats important! And i have just got my valve guide seals installed. Tomorrow im going to pick it up and hopefully get it all back togeather in the evening in time to go to the kiwibiker meet up in tauranga If i remember i will take photos of putting it back together.

[okeh]

Well sinse last time i posted about this the guy who was sending me the replacement piston and stuff finally looked at the piston he was gonna send me and found it had dents in the top of it ( probably not going to buy anything from them again ) , so i got my money back off him. I thought all was lost, but i found a really good piston and bore in Tauranga that i got cheap, the shop has just finished "refreshing" that which probably means a quick hone, and some other stuff. But the rings are all good so thats whats important! And i have just got my valve guide seals installed. Tomorrow im going to pick it up and hopefully get it all back togeather in the evening in time to go to the kiwibiker meet up in tauranga If i remember i will take photos of putting it back together.

Remember the con rod connects to the exhaust valve via the rear wheel.

[xwhatsit]

^Lol

You can get the valve springs out without a compressor. It's best to do with somebody's help, but put the head so it's sitting on something like a small paint pot (so you aren't resting on the studs, if you have those), and stuff a rag underneath so the valves can't push down. Then get an open-ended spanner and press down on the valves; on my 250 it was relatively easy, on your 400 it might require a bit more strength. Then your helper (or you if you have a articulated tail) just needs to pick out the little split collets (don't lose the bastards). Even easier to put it back again.

The valve seals are also very simple. Some long pliers to pull out the existing ones, and then the new ones are just a press fit. Don't need to spend money at a bike shop for that.

Remember; if you need cheap parts, Econohonda is your friend. http://econohonda.co.nz .

[mark247]

Well first off, i forgot to take photos. But i got it working! I cant believe it actually started first time. Sounded like a fish tank with no exhaust but who cares, it still started! I havent put the fuel tank on properly yet, or the seat, or anything like that, oh yeah and the exhaust obviously. But i managed to fix it! Im so surprised it works, i thought i would stuff something up.

By far the hardest part was the camchain tensioner and getting the chain onto the sprocket, i needed another set of hands for that but dad helped me with that which was good.

Oh and my brother had to help me put the piston into the cylinder, that was a bit tricky with the rings and all.

Other than that stuff it seemed to go smoothly.

I cant believe it actually works!!!!

[Kickaha]

^Lol

You can get the valve springs out without a compressor. It's best to do with somebody's help, but put the head so it's sitting on something like a small paint pot (so you aren't resting on the studs, if you have those), and stuff a rag underneath so the valves can't push down. Then get an open-ended spanner and press down on the valves

or get a tube socket same diameter as the valve collar and hit it with a hammer

[xwhatsit]

or get a tube socket same diameter as the valve collar and hit it with a hammer

Yeah I read that somewhere on the net, I tried it, but I was too scared to belt it with any force so it didn't work lol.


Glad to hear it's all back together. Putting the chain/sprocket/camshaft assembly back together is an absolute arse of a job, at least with that design (mine is the same). Done it a few times now but each time still get pinched fingers. Ghey.

[mark247]

I have a question.

To connect the sprocket for the camchain onto the cam shaft you use two bolts. They spin around and around with the camshaft obviously. I didnt use any locking agent on them at all, i just did them up reasonably tight and put it all together, i have ridden 100km without any problems. I was told it is a good idea to put locking agent on them because they could come lose from the spinning and vibrations.

What do you guys reckon i should do?

Keep riding it how it is or take the tappet cover off and lock tight them on?

Has anyone here not lock tighted them on before?

[okeh]

I have a question.

To connect the sprocket for the camchain onto the cam shaft you use two bolts. They spin around and around with the camshaft obviously. I didnt use any locking agent on them at all, i just did them up reasonably tight and put it all together, i have ridden 100km without any problems. I was told it is a good idea to put locking agent on them because they could come lose from the spinning and vibrations.

What do you guys reckon i should do?

Keep riding it how it is or take the tappet cover off and lock tight them on?

Has anyone here not lock tighted them on before?

Go get them welded with the biggest butiest weld ever! So they may never come out again~!

[xwhatsit]

I have a question.

To connect the sprocket for the camchain onto the cam shaft you use two bolts. They spin around and around with the camshaft obviously. I didnt use any locking agent on them at all, i just did them up reasonably tight and put it all together, i have ridden 100km without any problems. I was told it is a good idea to put locking agent on them because they could come lose from the spinning and vibrations.

What do you guys reckon i should do?

Keep riding it how it is or take the tappet cover off and lock tight them on?

Has anyone here not lock tighted them on before?

Put loctite on! That is exactly what caused my top end to seize. Either that or a loose camchain, I can't make up my mind. It's worth it.

Did you replace camchain btw?