What does rebuilding the top end mean?

[cbrsmurf]

?

Why is it more common on two strokes?

[HondaRider22]

OOH OOH pick me pick me

A top is is the upper half of the motor, it includes...

head
valves, valve seats, valve guides

bucket and shims, (the gap between the bucket and cams are measured to determined "valve clearance". Valves wear down after time and replacing the valve shims with bigger ones will make up for this difference and thus restore original engine performance) <---- edited

cams
cam chain and tensioners (which extend to the lower half of the motor)
spark plugs
exhaust manifold (headers)
Intake manifold (carb throttle body booties)
oil lines

etc...

anyways... a top end rebuild involves taking the valves out and grinding the valves and valve seats so that they seal and therefore restores engine compression. It also involves replacing any gaskets and seals including valve stem seals (which would cause your engine to burn oil if they are worn and leak)
A new head gasket is always replased when taking the head off.
If your engine blow a head gasket it would most likely burn water (white smoke).

I hope I came across clear...

[GetnJgyWitit]

good job mikey!

[Bryant]

Originally posted by SuzukiRider22
OOH OOH pick me pick me

A top is is the upper half of the motor, it includes...

head
valves, and valve seats
cams
cam chain and tensioners (which extend to the lower half of the motor)
spark plugs
exhaust manifold (headers)
Intake manifold (carb throttle boddies booties)
oil lines

etc...

anyways... a top end rebuild involves taking the valves out and grinding the valves and valve seats so that they seal and therefore restores engine compression. It also involves replacing any gaskets and seals including valve stem seals (which would cause your engine to burn oil if they are worn and leak)
A new head gasket is always replased when taking the head off.
If your engine blow a head gasket it would most likely burn water (white smoke).

I hope I came across clear...

Give this man a beer!!!

[cbrsmurf]

gracias bro

[GPTECHMAN]

alright next questions what are race cams gonna do?

[Ikazuchi]

Originally posted by GPTECHMAN
alright next questions what are race cams gonna do?

They change the timing on the valves. Usually the lobes are a bit higher/wider which will increase the time the valves are open - increasing breathing..lowering fuel economy, valve life, etc...

[Arnold_R1]

Originally posted by GPTECHMAN
alright next questions what are race cams gonna do?

The camshaft has been called the heart of the internal combustion engine, and there is a great deal of truth in this statement. The camshaft controls the valve train making possible the entire four cycle event. In stock American passenger car engines the camshaft is designed to deliver smooth quiet idling and good low speed performance. To acheive these ends as much as one fifth of the potential horsepower is sacrificed for two basic reasons. First, the valves are not moved off their seats radically, and second, the valves are not left open for long durations. Of course, there is some overlapping of the valves, and this is not particularly condusive to good performance, but at high engine speeds this overlap actually becomes beneficial as will be shown later.

A racing camshaft basically opens the valves higher and leaves them open longer than a stock camshaft. However, the exact profile of the cam, that is, how the cam actually accomplishes this event, is of primary importance. The ideal situation would have the intake valve snap open instantly at approximate top dead center ( TDC ) and remain open until 40° degrees after top dead center ( ATDC ). Unfortunately, such instantaneous action would pound the valve train to pieces and prove completely impractical. Therefore, even racing camshafts are a compromise between stock cams which activate the valve train only mildly and some yet-to-be invented instant valve opener.

Racing camshafts are designed to open the valves sooner and leave them open longer than stock cams, as well as lift the valves higher. The exact number of degrees that the intake valve opens ( BTDC ) and closes ( ABDC ), and the exhaust valve opens ( BBDC ) and closes ( ATDC ), depends of course on the grind. Each shaft is ground for a primary purpose, as explained later, but regardless of the grind there is more overlapping of the valves than with a stock cam. This overlap is inevitable because of the increased duration, but at high engine speeds some benefit is derived from the overlap as there is a mild supercharging effect of the exhaust gases which tends to suck in additional fuel and air. The basic reason for overlap can best be explained by an examination of the four cycle event.

The intake valve starts to open before the piston reaches TDC on the exhaust stroke of the previous cycle. In this way the valve will be fully open by the time the piston moves over TDC and down on the intake stroke. The incoming charge of fuel and air builds up a form of kinetic energy which causes the mixture to continue flowing into the cylinder after the piston has reached BDC and starts up on the compression stroke. The intake valve finally closes at some point 60° degrees or more ABDC so that there is no throttling effect on the incoming fuel which would cause a limitation on the engine's top speed performance. When the piston is at TDC on the power stroke both valves are closed to seal off the combustion chamber for the explosion of the fuel mixture. As the piston travels down on the power stroke the exhaust valve begins to open 60° degrees or more BBDC. A slight loss of power results from this early opening of the exhaust valve, but the overall effect is positive because the exhaust gases begin to escape the combustion chamber under their own power thus avoiding a throttling effect on the piston as it moves up on the exhaust stroke. The exhaust valve remains open after the piston has reached TDC because the kinetic energy built up by the escaping gases actually causes the gases to continue to flow even when the piston has started down on the intake stroke. The piston's transition at TDC from exhaust stroke to intake stroke is precisely the area where overlap occurs. As illustrated by this review of the four cycle event, the exhaust valve is open ATDC to allow more complete scavenging of the chamber, while the intake valve opens BTDC to facilitate the flow of the incoming charge. The actual amount of overlap can be quite large, especially in camshafts designed for top end performance. As previously explained, this large overlap will effect low speed performance to such an extent that the car may even run slower at low r.p.m.'s with the racing cam than it did with the stock cam. For this reason great care should be exercised when deciding which cam should be used in an engine.



WHOA! My fingers are tired!
:rolleyes:

[HondaRider22]

Good job Arnold. Good stuff to know, I sure learned something today.

In addition to the cam question I'd like to add what cam chain (CC) and cam chain tensioner (CCT) are, incase you do not fully understand.

The lower part of the motor consists of an engine block, crank, rods and pistons (lets just keep this simple for now), anyways the crank spins and is linked to the transmission which spins the front sprocket... you know where this is leading...

So, the crank also spins the cams via a chain (there is a gear on the crank and the cam of which the chain rides on). The CCT keeps the CC nice and tight so that the top end of the motor and the bottom half operate in sync. That CCT wears out and therefore doesn't keep the CC as tight and begins to vibrate and "slap" making a noise.

[cbrsmurf]

Originally posted by SuzukiRider22
Good job Arnold. Good stuff to know, I sure learned something today.

In addition to the cam question I'd like to add what cam chain (CC) and cam chain tensioner (CCT) are, incase you do not fully understand.

The lower part of the motor consists of an engine block, crank, rods and pistons (lets just keep this simple for now), anyways the crank spins and is linked to the transmission which spins the front sprocket... you know where this is leading...

So, the crank also spins the cams via a chain (there is a gear on the crank and the cam of which the chain rides on). The CCT keeps the CC nice and tight so that the top end of the motor and the bottom half operate in sync. That CCT wears out and therefore doesn't keep the CC as tight and begins to vibrate and "slap" making a noise.

can a bad cct cause "irregular" timing and would it cause engine damage?

[HondaRider22]

Originally posted by cbrsmurf
can a bad cct cause "irregular" timing and would it cause engine damage?

A bad cct would in theory cause the timing to be off but only to micro amount and would not be noticed by the operator. I'm sure that the highest performance motors with the a highly tuned rider would notice. And no a bad cct wouldn't cause engine damage unless an extreme case would occur in which a cct got really old and worn and broke or the chain snapped...(I really highly doubt that would ever happen)

[deathblow]

Originally posted by cbrsmurf
can a bad cct cause "irregular" timing and would it cause engine damage?

I had the CCT problem on my F4i. I never noticed anything performance or functionaly, but the ticking was sure annoying. The shop replaced it twice for me and the third (updated CCT) worked fine, or at least never started ticking.

[Arnold_R1]

Originally posted by deathblow
I had the CCT problem on my F4i. I never noticed anything performance or functionaly, but the ticking was sure annoying. The shop replaced it twice for me and the third (updated CCT) worked fine, or at least never started ticking.

I think that was common problems with F4i's! I think Honda had a recall on them, fixed for free so I hope you didn't pay each time? :eek:

[deathblow]

Originally posted by Arnold_R1
I think that was common problems with F4i's! I think Honda had a recall on them, fixed for free so I hope you didn't pay each time? :eek:

It was free, it was a well documented problem and the dealerships were aware of the problem.