Sanity check on engine geometry

Portofino said:
There will be no position on the cross planed crank whereby all the valve s are closed
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Agreed.
I don't think I'll ever bother going through the math, but unless someone knows better, I think the right answer to the question about the position where all valves are closed in a V8 is, more than likely, "none". :encouragement:

I also agree that the whole barring exercise is very far from being essential, of course.
Then again, neither is pleasure boating as a whole... :D

On a different note, a W16?
You had a Bugatti and never published a thread with a lot of pics about it?
Shame on you, PF! :rolleyes:
 
petem said:
Why are we even discussing MapisM's pointless barring
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Oi, careful there.
If we should refrain from posting pointless debates (like those on silly outdrives powered boats, just as another example :p) we could as well shut the whole asylum down... :cool:
 
MapisM said:
PS: coming to think of it, another interesting question would be is there's any crankshaft position in which ALL valves are closed.
Of course, this DOES depend on the number of cylinders (obviously such position exists, in a single cyl engine, but that becomes more difficult to guess as the number of cyl grows). And of course, knowing the initial position would be a must.
I'm just wondering if in a V8 there's any position inside the whole 720° cycle where all valves are shut.
Gut feeling tells me it's unlikely, but this time I really have no idea - any thoughts welcome!
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As you say, depends on number of cyls and lots of other factors, unlike the prev Q. The valves are open for 1/4 of the 720 deg cycle, and on same precise assumptions as before, if an 8 cyl engine were set up to fire in 4 pairs of 2, then there is a point at which all valves are shut. But in real life with valve timing overlaps, and the 8 cylinders firing sequentially, the answer is no.
 
jfm said:
As you say, depends on number of cyls and lots of other factors, unlike the prev Q. The valves are open for 1/4 of the 720 deg cycle, and on same precise assumptions as before, if an 8 cyl engine were set up to fire in 4 pairs of 2, then there is a point at which all valves are shut. But in real life with valve timing overlaps, and the 8 cylinders firing sequentially, the answer is no.
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Without looking up the firing order ,I think they will fire seperately ,
Imagine the unnecessary potential twist on the crank if a pair fired off together , ( one in each bank ) particularly if not next to each other .
Worse still in a V 12 ,
I reckon they take it turns one at a time .
I realise all is nice n tight crank tightly clasped to its journals , big end bearings all new n shiny not a 0.000001 mm or what ever of play when new and 20 hrs old .——when the factory sign it off and the engineers disappear :)
— But 10 y later or more -after a few dodgy oil changes , more of low load ,useage than expected , abrasive and acid contamination of the oil , with the thing sat doing nothing for months on end , then things start to loosen up .
A couple of pistons boxing it out , there is in fact 4 sets is gonna swing the longevity meter to the left .
 
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jfm said:
As you say, depends on number of cyls and lots of other factors, unlike the prev Q. The valves are open for 1/4 of the 720 deg cycle, and on same precise assumptions as before, if an 8 cyl engine were set up to fire in 4 pairs of 2, then there is a point at which all valves are shut. But in real life with valve timing overlaps, and the 8 cylinders firing sequentially, the answer is no.
Click to expand...
I like your reasoning method - straightforward and uncomplicated.
Agreed 100%, that's already enough to tell that such point doesn't exist! :encouragement:
 
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