SpitfireS

It is a popular myth: during an overrev the valves stay open or “they float” long enough for the cam to come around and hit them on the head.
This repeated “hammering” during the overrev cracks retainers.
This is not true.

The short explanation is this: the valve spring will accelerate the valve upwards as soon as it gets the chance.
Once this has started it simply does not decelerate the valve somewhere during the valve stroke to not close it or make it “float”.

The longer explanation is this:
Let’s divide the cam’s cross section up into 4 quarts: 1 quart opens the valve, 1 quart closes the valve and 2 quarts do nothing.
Okay.. this is wrong as explained in post #52.
It is less, one piston cycle is 1/2 a crank turn = 1/4 cam turn so everything has to happen in about 1/4 cam turn, opening and closing.
See post #52 for details.
In a 4-stroke engine this nothing bit is either the intake-compression-combustion cycle when we look at it from the exhaust valve’s point of view or the compression-combustion-exhaust cycle when we take the intake valve’s point of view.
In either case: the piston moves up and reaches TDC once during the nothing bit of the cam.

From now on I’m only talking about the exhaust valve.
Our engine is an interference motor, IOW when the valves do not move up enough they get hit by the piston.
This is the danger zone.
Overrev high enough and you will end up with bend valves: how much more proof do you need?

The danger zone is not the full stroke of the valve, IOW the valve does not have to be fully closed to not get hit by the piston.
I don’t know exactly how long the danger zone is, people that have swapped retainers without removing the head could tell if the tried moving the valve down with the piston at TDC.
It doesn’t really matter how long the danger zone is either, it is there.

So during an overrev without piston & valve contact the valve was able to move up fast enough to stay out of the danger zone while the piston moves up.
Yet, according to the myth, it did not close during the 2 quarts of the nothing bit of the cam.
The myth suggests the valve will decelerate once it is out of the danger zone and linger around or float and not close.

Another way to show the non logic of the floating valve myth is the difference in time it has to take to close the valve below overrev situation and above overrev situation (but below piston & valve contact)
Normally, the closing time of a valve is a quarter cam turn.
To float it suddenly has to take 3 x more time and still not close.
This can not happen and it does not happen.

Myth busted.


How do retainers get cracked during an overrev?
Easy.
The valve does accelerate all the way up but can not keep up with the cam.
This results in the valve hitting its seat at speed, instead of being guided onto its seat by the cam.
So the valve, reatainer and spring are at high speed and suddenly stop.
This cracks retainers.
And.. it could damage valve seats if it happens often enough.

So, does it really matter why retainers crack?

Yes it does.

If you are the first owner and are truly sure you never overrev’d and find cracked retainers you have a problem with valves moving too slow for some reason.
One of those reasons can be bad valve guides.
A reason for bad guides can be fuel or oil - or both - related: during the exhaust stroke deposits left on the exposed valve stem wear out the valve guide.
Maybe, eventhough you have 3 bars (or whatever AP2’s have J ) of coolant temperature your engine is still to cold for VTEC.
This means you may have damaged seats and damged guides as it may have happened more than once and who knows for how long.

If you are not the first owner and you find cracked retainers it means the engine may have everything mentiond above and add overreving.
If your solution is to replace retainers - or have it done - without removing the head and call it a day you are taking a risk IMO.
To reduce this risk a leak down test can show some problems, if it is clear the leak is caused by the valves.


Oh.. btw.. to use valve clearance as a check for cracked retainers is a BIG FAIL.
Cracked retainers move up the valve stem and do not change valve clearance.
There are lots of posts with exellent explanations and clear photo’s to find about this.


Another thing about AP1 (early F20) retainers: they are not weak.
A weak retainer would break in 2 pieces as soon as the crack is there.
You will notice this as the valve will drop = engine toast.
If parts get damaged because they are forced to deal with situations they were not designed to deal with does not mean they are weak.

zeroptzero

I always thought the move to ap2 retainers on an ap1 would increase the cnances of valve float if they are a heavier part. We haven't seen many examples of that so your theory could help explain why we haven't seen increases in valve float. Feel free to correct me if I'm wrong.

davidc1

Interesting.....but it was really hard to read this because of all the bad grammar, spelling, punctuation, etc. Where did you copy it from?

davidc1

And some of it simply doesn't make sense because of the bad English. Like this:

Another thing about AP1 (early F20) retainers: they are not weak.A weak retainer would break in 2 pieces as soon as the crack is there.

So....a crack is there....but it's not "weak"....but it's cracked.....but it's not in two pieces [or three or four, or "quarters" (like in the beginning of the post, whatever that meant)]....so it's not weak....but it's cracked....don't get it....

You will notice this as the valve will drop = engine toast. If parts get damaged because they are forced to deal with situations they were not designed to deal with does not mean they are weak.


But the valves have dropped slightly.....and some more so....and people have had toasted engines.....so what are AP1's subjected to that AP2's aren't?

zeroptzero

Not totally unreasonable from someone that lives in Euorope, so English wouldn't be his first language. Cut him a bit slack, just a bit though

davidc1

Ok, you're right. I didn't notice that. My apologies to the OP.

Although it was copied from somewhere, so I'm still curious about that....

nofearofdanger

Ok, you're right. I didn't notice that. My apologies to the OP.

Although it was copied from somewhere, so I'm still curious about that....
[/quote]

What makes you think it was copied? Maybe the different font meant he wrote it in a word processing program before he pasted it onto here... who knows
Either way, good read.

zeroptzero

I think he had a few Heinekens when he was writing it, lol . j\k

davidc1

Ok, you're right. I didn't notice that. My apologies to the OP.

Although it was copied from somewhere, so I'm still curious about that....
[/quote]

What makes you think it was copied? Maybe the different font meant he wrote it in a word processing program before he pasted it onto here... who knows
Either way, good read.
[/quote]

It's possible, but, I feel like I've read it somewhere before.

Also, he doesn't "introduce" the subject or his post at all. It's just, bam, and it's there.

We'll see when the OP comments.

davidc1

heh heh....I always like the cool tops on the Grolsch bottle better!