My engine will need a re-build soon.

What I wanted to know is from people that have re-built previously is will I need new pistons?

I can tear down the engine and do measurement that will tell me if I need to go oversize, but for you engine was the bore that bad that it required it?

 

I'm surely no expert, but if your rings are shot you'll get blowby and lose compression and thus lose power. However, if this is the case and if the cylider and pistons are within factory spec and not otherwise damaged, you shouldn't need to bore out or to replace the pistons. You would need to replace the rings, though,which probably can be done with the engine in the frame. You will have to pull the head.

 

Trips how many miles are on your bike? What makes you think that you will need a rebuild soon?
Yes you can measure the bores, but unless you have a real accurate bore dial indicator and experience, this is a job for the machinist. He'll be able to tell you if you need to overbore. If that's the case then you'll need pistons.pins and rings. You might as well also check the rods and crank and see if you need to resize the rods as well. Valve job and probably all new valves, springs retainers, etc.
It might be less expensive to find a low mileage engine and swap it out.

 

Trips, it depends on the engine. How often was the oil changed and with what, how high of an RPM was the bike shifted at or how burdened was the engine at low RPM and things like operating temperature and air filter quality are factors in engine life.

As an engine ages, the bore wears more on top than on the bottom due to the higher stresses mostly caused by the air/furl mixture being ignited at the top of power stroke and becoming exhausted more toward the bottom of the stroke. How many times the piston goes up and down contribute to this ring to wall wear. This is the cylinder run out. Most engines allow .015� from top to bottom run out. It can be measured by measuring the bore diameter just under the ridge and at the bottom of the stroke where the rings still contact the cylinder wall.

Also, due to the stress of the piston being pushed in a downward direction against the connecting rod which is connected to the crank shaft, the angle of the connecting rod causes the piston to tilt and this in turn creates wear on the front of the cylinder wall. This is measured in cylinder ovality and is attributed to how much throttle is being used.

Overall cylinder wear can be measured buy the difference between the diameter just below the ridge and the ridge itself.

You may already know this, I am only trying to state the fact that engine wear depends on how you ride and maintain the bike. For the forum members shifting in the red all the time, 30,000 miles may equal a lot of wear. For others shifting around 4,500 to 5,000 RPM, they may see the same amount of wear at around 100,000 to 120,000 miles. The bikes shifted at the lower RPMs will have far less stress on the lower bearings than the high RPM engines. When you think of it, an engine turns twice as much at 10,000 RPM than it does at 5,000 RPM and those Revs are very stressful ones causing a lot of wear compared to low RPM.

The only way to predict your engine wear is to ask yourself how you have been treating your bike and wonder how other owners have been treating it.
If you decide to rebuild without boring it out, don’t forget to break the ridge.

EDIT: spelling

 

Bikes only done 100k's.

When commuting and normal riding its ridden sedately. But on weekends I do 300-400km's of open roads with the rpm rarely below 8,000rpm.

I scored an engine of Ebay for $130 . So I am going to re-build that and swap it. The engine doesn't need rings atn but I want to be able to drop in an engine that is in new condition so I can forget about anything other than maintenance for a few years.

But because I am a tight **** I can save a lot of $$$ if I only need to re-ring it and give it a hone.

 

It looks like you can do a lot without removing the upper and lower cases. I dropped a nut while changing the CCT and pulled the lower pan off to look for it. While I was looking up I noticed that it looks like it is possible to unbolt the connecting rods and pull the pistons out the top with the head off. If your transmission is working fine you may want to save work and take that route.

 

To get the pistons off you must take the pots off as these only go in one way. Once the head is off then there is only one retaining bolt at the front of the engine. Careful of the locating dowels as these may have rusted in, and then you may need to give it some incouragement to seperate. As a footnote, if the y shaped waterpipe at the front does not wany to move then dont force it as it is only a mild chrome steel (as I found out to my cost) £57))[sm=nothatway.gif] and bends like you would'nt beleive, sh*t[sm=boosign.gif], and they are not always available. Some parts of the engine are no longer made, so take care.

I would post some pics, but for some reason I can't remember how. Please adise[sm=Flahssssss.gif]




[sm=bounceybounce.gif]

 

The replacement motor has a dud starter clutch so I'll have to split the cases anyway.

BTW if you ever need to replace that chrome waterway pipe a radiator shop may be able to make some for you. They have a tool that puts a lip on pipe to give hose something to slip over and be clamped.

 

It is possible to take out the starter clutch without seperating the crank halves, just remember that you must lock off the alternator tensioner first, (easier said than done I know). What year is the new engine Trips?

 

Is this tensioner manual or automatic?