Valve/Cam timing Petrol 2.25- am I over thinking this??

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MFC

MFC

Active Member
Posts
161
Timing 2.25.jpg Hi All,
Currently rebuilding my 2a and the engine after a 40thou rebore. All going well and have put the cam in ok. Setting up the valve timing as per book (both green and haynes) lined up the cam sprocket with the P on key and the other P to the bolt hole all ok. AndI have the crank at TDC (keyway up) first by eye and then by dti, and all is as it should be.
My understanding is that TDC is on the compression stroke, right? well if that is the case why is inlet valve 2 open when lined up with the P?????. It looks like it is to my thinking 180 deg out or have I made a school boy error here - a bit confused. Any thoughts??
Cheers
 
Last edited:
A Few other pics of where we are aim to be on the road end of April
 

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MFC said:
View attachment 235591 Hi All,
Currently rebuilding my 2a and the engine after a 40thou rebore. All going well and have put the cam in ok. Setting up the valve timing as per book (both green and haynes) lined up the cam sprocket with the P on key and the other P to the bolt hole all ok. AndI have the crank at TDC (keyway up) first by eye and then by dti, and all is as it should be.
My understanding is that TDC is on the compression stroke, right? well if that is the case why is inlet valve 2 open when lined up with the P?????. It looks like it is to my thinking 180 deg out or have I made a school boy error here - a bit confused. Any thoughts??
Cheers
Click to expand...
yes your 180 degrees out
 
Quick up date - after looking at the picture I posted it looks like, due to the angle of the engine stand I was aligning with the wrong hole on the timing case. Now it seems that when aligned with the top hole, the cam is on the overlap between exhaust and inlet - is this ok?? still seems odd to me
 
I've discussed angular definitions with @jamesmartin here, before! :D

If the cam is 180 degrees out, I think you want to rotate the crankshaft by one turn. 360 degrees on the crank will give you 180 degrees on the camshaft. That's what you need, isn't it?

And you probably don't want to go turning the crank when the timing chain is off. Best part it at 90 degrees off TDC (so the pistons are all at half stroke), and then you can rotate the camshaft to suit, without having to worry about the pistons hitting the valves. If you're moving the crankshaft, you really need to be sure the camshaft is synchronised so the valves are shut enough when the pistons reach the top of their stroke,.
 
MFC said:
Quick up date - after looking at the picture I posted it looks like, due to the angle of the engine stand I was aligning with the wrong hole on the timing case. Now it seems that when aligned with the top hole, the cam is on the overlap between exhaust and inlet - is this ok?? still seems odd to me
Click to expand...
It does sound like you're at the end of the exhaust stroke, not the compression stroke.
 
TheMegaMan said:
It does sound like you're at the end of the exhaust stroke, not the compression stroke.
Click to expand...
I agree, not sure how to proceed as both valves should be closed in compression and I have it set up as per book, can't be the crank in wrong position as chain not on!
 
MFC said:
Quick up date - after looking at the picture I posted it looks like, due to the angle of the engine stand I was aligning with the wrong hole on the timing case. Now it seems that when aligned with the top hole, the cam is on the overlap between exhaust and inlet - is this ok?? still seems odd to me
Click to expand...
you want no1 valve lobes pointing down no4 both pointing up
 
jamesmartin said:
you want no1 valve lobes pointing down no4 both pointing up
Click to expand...
thanks James will have a look tomorrow and see if I can make sense of this. Wonder whether the camshaft sprocket could be a replacement (from another engine) or something like that but I think most cams were the same in the series world at that time.
 
If you need to realign the camshaft and the chain is off, you probably want to back the crankshaft up by 90 degrees, and then it will be safe to rotate the camshaft into the correct position. Lock it in place, and then turn the crank back up to TDC. But you need to be really sure the valves are in a 'safe' position before letting the pistons back up to the top again.
 
TheMegaMan said:
If you need to realign the camshaft and the chain is off, you probably want to back the crankshaft up by 90 degrees, and then it will be safe to rotate the camshaft into the correct position. Lock it in place, and then turn the crank back up to TDC. But you need to be really sure the valves are in a 'safe' position before letting the pistons back up to the top again.
Click to expand...
Ok thanks but at the moment the head is off as is the chain do we should be safe here
 
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