172 cam timing, cam won’t stay in place

[Alhitch]

Hi

Me and my friend have been trying to time his 172 engine after we had to reseal the rocker cover.

After looking at various videos of how people time them up we got the correct tools and went to give it a go. Only problem is the inlet cam won’t stay in place, it seems to spring back to where we moved it from when trying to move it to line it up with the exhaust cam.

Is there anything in particular we might be doing wrong? The crank is in TDC and we haven’t put the cam pulleys back on yet. Only option left is to refit the pulleys and cambelt and see if that helps. But I’m reluctant to try that as we may potentially cause damage to the engine... if we haven’t already!

Any help would be appreciated

Thanks

Alex

 

[Crayola]

@bloke

 

[JamesBryan]

I doubt it should be springing back.

Have you got the horseshoe tool in the slotted end yet?

 

[Alhitch]

I doubt it should be springing back.

Have you got the horseshoe tool in the slotted end yet?

No that’s why we’re trying to turn it so we can line up the horseshoe tool up but when you get it roughly in place it just goes back to where we moved it from, there not far off. It just makes me think we’ve broke something in the process aha

 

[Crayola]

Have you taken the plugs out?

 

[JamesBryan]

No that’s why we’re trying to turn it so we can line up the horseshoe tool up but when you get it roughly in place it just goes back to where we moved it from, there not far off. It just makes me think we’ve broke something in the process aha

Cams 180 degrees out maybe and it's trying to open the valves as you turn it?

Take a pic of where the slots are now.

 

[Brigsy]

It will spring to a different position with no horseshoe or cam pulleys on due to the valve springs and valves opening. Do it as per the workshop manual

 

[Alhitch]

It will spring to a different position with no horseshoe or cam pulleys on due to the valve springs and valves opening. Do it as per the workshop manual

Thanks pal, that seems logical, where can I get a workshop manual from, that would be a if help rather than relying on YouTube!

 

[JamesBryan]

Thanks pal, that seems logical, where can I get a workshop manual from, that would be a if help rather than relying on YouTube!

The pistons need to be at mid travel before you try and move the cams round, otherwise the valves will hit them. Then set to TDC once the horseshoe is in.

 

[Alhitch]

The pistons need to be at mid travel before you try and move the cams round, otherwise the valves will hit them. Then set to TDC once the horseshoe is in.

Thanks a lot mate, I’ll give a read now and have another, that looks where we’ve been going wrong

 

[JamesBryan]

Thanks a lot mate, I’ll give a read now and have another, that looks where we’ve been going wrong

Page 11 explains what i've just mentioned.

 

[Alhitch]

Page 11 explains what i've just mentioned.

Yeah makes sense now, hopefully no damage has been done. Is there any particular way you know when your pistons are at mid travel? Might be simple but this is all new stuff to me aha

 

[JamesBryan]

Yeah makes sense now, hopefully no damage has been done. Is there any particular way you know when your pistons are at mid travel? Might be simple but this is all new stuff to me aha

Stick a long screwdriver down the spark plug holes and watch it go up and down when you turn the engine over, then stop about middle.

 

[Alhitch]

Stick a long screwdriver down the spark plug holes and watch it go up and down when you turn the engine over, then stop about middle.

Cheers mate

 

[Touring_Rob]

Have you taken the plugs out?

Shouldn't matter at all if the plugs are still in, he is turning the cam not the crank.

Remember to manually rotate the engine by a minimum of two full revolutions BEFORE trying to start it.

 

[Crayola]

Shouldn't matter at all if the plugs are still in, he is turning the cam not the crank.

Remember to manually rotate the engine by a minimum of two full revolutions BEFORE trying to start it.

True just re-read?‍♂️?

 

[Touring_Rob]

True just re-read?‍♂️?

I only picked up on it because the same though popped into my head before having another read

 

[Brigsy]

Make sure you have the crank pin in when the flywheel is on the 0deg mark on the bellhousing, as easy to pin the crank balance hole instead of the actual tdc slot