i can see where Colin is coming from actually cause when
1 is at TDC compression (all closed)
cylinder 2 is BDC power (just about to open for exhaust)
cylinder 3 is BDC intake (intake is just about fully closed)
and cylinder 4 is TDC exhaust (just about to open intake)
so with that being said there are a few points through out the cycle where the valves are either closed or mostly closed or barely open leaving quite a bit of room for the belt to break and stop cam rotation and leave room for the piston to still do its thing
hope that all makes sense and REALLY hope i thought that through right and dont make this worse lol
having two heads in my possession right now that are complete, when I went home for lunch today I tested an idea that I had. I remembered when I was taking the a1 head off of the block, that all of the valves were closed (or near closed). and I have a c1 head sitting on my bench that is still put together and that one is again the same way, all closed. so while I was home I tried spinning the cams a few times, and both heads had the same result.
when turning the cams, you can feel resistance to the valve springs as the valve opens and the lobes on the cams turn. after reaching the apex of the lobe and crossing it, it would rotate itself back into the all closed position. (with a springy like motion)
so, my theory is,
there is a chance that at higher rpms, that if the belt were to break, that the cams are going to continue to rotate until they slowdown enough for the valve springs to have the upper hand, and hold them in that position. but, during that time, there is a chance that your piston will hit a valve, for the fact that it may not take that long for the cams to stop, but, if your driving down the road and it snaps, you still have the wheels turning over the bottom end of the motor until you either stop (for the auto guys) or push in the clutch. there for giving a chance that on any particular cylinder the piston is at full stroke and the valve is fully opened.
so that’s the way I feel about it. there is always a chance, like everyone else has said. get yourself a new belt, get the timing right and do a leak down. that’s the only true way to tell.
Stock b18a’s have a low chance of piston to valve contact due to a lower cam lift and duration and a relatively large piston-to-valve clearance. However, damage may still be possible, especially if the engine was high reving at the time of the break.
As nicholsLS said, with no timing belt, the cams will have a tendency to stop at the point of least net spring load (from the valve springs pushing on it). I dont have a cam with me atm, but this should theoretically be when all the valves are all midway through their lift (slightly open/closed). This theory seems to back up what iRockTheDA9 observed in that the valves were all slightly closed. However, iRockTheDA9’s post is a little bit misleading since it is impossible for ALL valves to be completely closed at the same time. (Honda cam lobes always have an overlap).
This means that the possibility of piston-to-valve contact is relatively low on stock engines, but the possibility will increase depending on the rpm at which the belt broke. With highly modded engines the potential for contact is significantly higher, and is a totally different story.
I did not deny that the B18 was an interference engine. For the last time, IT IS an interference engine. In fact almost all modern engines are interference engines. The definition of an interference engine just means that the valves are able to extend past the face of the head, and have the potential of colliding with the piston upon improper timing.
But the clearances in a stock B18a are loose enough that the possibility of contact when a belt snaps is not that high.
I did say that it is impossible for all the valves to be completely closed simultaneously in Honda’s. All I said was that the cams will have a tendency to stop where all the valves are slightly open. Learn to read before making comments please.
[QUOTE=wise_old_dragon;2175246]I did not deny that the B18 was an interference engine. For the last time, IT IS an interference engine. In fact almost all modern engines are interference engines. The definition of an interference engine just means that the valves are able to extend past the face of the head, and have the potential of colliding with the piston upon improper timing.
But the clearances in a stock B18a are loose enough that the possibility of contact when a belt snaps is not that high.
I did say that it is impossible for all the valves to be completely closed simultaneously in Honda’s. All I said was that the cams will have a tendency to stop where all the valves are slightly open. Learn to read before making comments please.[/QUOTE]
Getting a bit defensive there aren’t you? I never quoted you. I made a general comment on the lameness of this thread.
If you actually read my post it states: [QUOTE=therealkroysc;2175174]This thread is full of lolz. Valves returning to closed when the belt snaps. Non interference engine.[/QUOTE]
Cheers!
I will make a somewhat useful addition to this thread. I have seen a few Honda’s that managed not to bend valves on a snapped belt. A BS1 (mine personally), D17A2 and a JDM F22B. But I have seen about 2 dozen that had valve damage including a B20Z and B18C1. I’ve even seen A H22A1 bust a piston at high rpm under N20 when the belt snapped. It was extremely nasty and trashed the entire inside from the internal shrapnel, even the crank was not salvageable. If a belt breaks and the valves are fine then its like dodging a bullet.
An Interferance motor means that it is POSSIBLE to bend valves is the belt breaks. Is it a guarantee that valves will bend? No… simply that it is possible. As previously stated, different series of motors are going to have a different percentage/chance of this happening.
A Non-Interferance motor means that any piston at its highest point can NOT hit any valve when it is completely open. So no matter the speed/rpm of the motor or mechanical timing or any other reason, there will not be any p2v contact whatsoever.
If the belt has broken, install a new one and properly time the motor, and do a leakdown. That will tell you if more work needs done or not.
I will make a somewhat useful addition to this thread. I have seen a few Honda’s that managed not to bend valves on a snapped belt. A BS1 (mine personally), D17A2 and a JDM F22B. But I have seen about 2 dozen that had valve damage including a B20Z and B18C1. I’ve even seen A H22A1 bust a piston at high rpm under N20 when the belt snapped. It was extremely nasty and trashed the entire inside from the internal shrapnel, even the crank was not salvageable. If a belt breaks and the valves are fine then its like dodging a bullet.[/QUOTE]
these motors that you’ve seen bend valves on a “snapped” t-belt (or at least the ones that you’ve mentioned) are close interference. much less clearance between the valves piston head.
stock b18a1’s are very forgiving.
i’ve personally broken a t-belt in one and everything was fine.
in another, my exhaust cam seized, causing the belt to skip about 180 degrees. i reset the timing and it ran fine (until a couple days later when the cam seized again, of course and it was out with that motor, but you get the point)
they are not close interference.
