Finding TDC with engine in situ
Discussion
Just need a little advice on finding TDC with a dial gauge with the engine in situ. I previously used the 'engineered spark plug method' while the chain was off; however i dont think this will work now as it requires the crank to be rotated both clockwise ,then anticlockwise - which i feel wouldnt be good with the chain in place - moving the tension over the other side etc etc.
Following a rebuild - it has come to light that the TVR workshop manual is pointless with regards to engine timing, as it leads you to believe that the valve overlap on cyl 1 and 8 should be set when the crank is midway between the TDC on both banks. This is subsequently incorrect/or at best; completely pointless!, as it will not allow the engine to rev over 5500rpm, as we've found out the hard way! So now with engine in situ, we must lift the rocker covers and fiddle around setting up each bank in accordance with its own TDC - Hindsight is a wonderful thing!
Any advice on peoples methods of finding TDC's with engine in situ would be much appreciated. Just oredered a Sealey dial gauge etc, but how is best to mount it to get a nice accurate reading?
Cheers
Following a rebuild - it has come to light that the TVR workshop manual is pointless with regards to engine timing, as it leads you to believe that the valve overlap on cyl 1 and 8 should be set when the crank is midway between the TDC on both banks. This is subsequently incorrect/or at best; completely pointless!, as it will not allow the engine to rev over 5500rpm, as we've found out the hard way! So now with engine in situ, we must lift the rocker covers and fiddle around setting up each bank in accordance with its own TDC - Hindsight is a wonderful thing!
Any advice on peoples methods of finding TDC's with engine in situ would be much appreciated. Just oredered a Sealey dial gauge etc, but how is best to mount it to get a nice accurate reading?
Cheers
I use a piece of rubber hose that just fits into the spark plug hole and a bottle of kiddys bubble mix. Screw the hose into the number 1 (or number2) plug hole and turn the crank pulley clockwise until both valves are closed. Dip the tube in and out of the bubble mix to leave a film over the end and keep turning the crank. As the piston rises in the bore a bubble will be blown and as it passes TDC it will shrink again.
As soon as you see the shrinking make a mark on the AC pulley (I use a home made pointer bolted to the washer bottle bracket as a reference mark) This gives you a rough TDC. To get the accurate position I keep turning and when I am nearly at the rough mark, I wipe and re-dip the tube. This gives a much smaller bubble that is far easier to see when it stops growing. Mark again with a scribe for your accurate TDC mark.
It may take a few tries to get the hang of this, but when you do it is as accurate as a dead stop or dial gauge. The longer the lever you have on the crank pulley - the easier it is to make the very fine movements you need to hit exactly TDC.
If you have a thin bore tube with the soap film just over the end - you can see the film moving very accurately indeed - to within a fraction of a degree.
Once you have TDC for the front cylinder on each bank marked, you want to set the cam timing to equal lift on valve overlap at TDC.
Turn the cam so that the followers on cylinder 1 (or 8 - they are 180 apart) are under the cam lobes (one is closing the other opening) and adjust so that they are exactly level. Put the cam pulley back on and tighten the timing chain, then adjust the crank to your TDC mark (with the cam pulley slipping on the shaft). Once you have them lined up you should be able to get the top 2 bolts in (with loctite!!) then turn the crank so the cam turns 180 to get the other two bolts in.
Having just done this job - I found that if you try to over tighten the first cam pulley bolts it is possible to shift the cam slightly and loose your timing, so care is needed.
Repeat for the other bank.
As soon as you see the shrinking make a mark on the AC pulley (I use a home made pointer bolted to the washer bottle bracket as a reference mark) This gives you a rough TDC. To get the accurate position I keep turning and when I am nearly at the rough mark, I wipe and re-dip the tube. This gives a much smaller bubble that is far easier to see when it stops growing. Mark again with a scribe for your accurate TDC mark.
It may take a few tries to get the hang of this, but when you do it is as accurate as a dead stop or dial gauge. The longer the lever you have on the crank pulley - the easier it is to make the very fine movements you need to hit exactly TDC.
If you have a thin bore tube with the soap film just over the end - you can see the film moving very accurately indeed - to within a fraction of a degree.
Once you have TDC for the front cylinder on each bank marked, you want to set the cam timing to equal lift on valve overlap at TDC.
Turn the cam so that the followers on cylinder 1 (or 8 - they are 180 apart) are under the cam lobes (one is closing the other opening) and adjust so that they are exactly level. Put the cam pulley back on and tighten the timing chain, then adjust the crank to your TDC mark (with the cam pulley slipping on the shaft). Once you have them lined up you should be able to get the top 2 bolts in (with loctite!!) then turn the crank so the cam turns 180 to get the other two bolts in.
Having just done this job - I found that if you try to over tighten the first cam pulley bolts it is possible to shift the cam slightly and loose your timing, so care is needed.
Repeat for the other bank.
Edited by Tanguero on Thursday 23 September 09:02
An old guy who lived next door to me (probably long dead now) showed me this when I was working on my first car 35 years ago.
I know it sounds a weird way of doing it - but it always amazes me just how sensitive a method it is.
You are using the hydraulic advantage to 'amplify' the piston movement in the air column in a much narrower tube.
Tanguero said:
I use a piece of rubber hose that just fits into the spark plug hole and a bottle of kiddys bubble mix. Screw the hose into the number 1 (or number2) plug hole and turn the crank pulley clockwise until both valves are closed. Dip the tube in the bubble mix and keep turning the crank. As the piston rises in the bore a bubble will be blown and as it passes TDC it will shrink again.
As soon as you see the shrinking make a mark on the AC pulley (I use a home made pointer bolted to the washer bottle bracket as a reference mark) This gives you a rough TDC. To get the accurate position I keep turning and when I am nearly at the rough mark, I wipe and re-dip the tube. This gives a much smaller bubble that is far easier to see when it stops growing. Mark again with a scribe for your accurate TDC mark.
It may take a few tries to get the hang of this, but when you do it is as accurate as a dead stop or dial gauge. The longer the lever you have on the crank pulley - the easier it is to make the very fine movements you need to hit exactly TDC.
If you have a thin bore tube with the soap film just over the end - you can see the film moving very accurately indeed - to within a fraction of a degree.
Once you have TDC for the front cylinder on each bank marked, you want to set the cam timing to equal lift on valve overlap at TDC.
Turn the cam so that the followers on cylinder 1 (or 8 - they are 180 apart) are under the cam lobes (one is closing the other opening) and adjust so that they are exactly level. Put the cam pulley back on and tighten the timing chain, then adjust the crank to your TDC mark (with the cam pulley slipping on the shaft). Once you have them lined up you should be able to get the top 2 bolts in (with loctite!!) then turn the crank so the cam turns 180 to get the other two bolts in.
Having just done this job - I found that if you try to over tighten the first cam pulley bolts it is possible to shift the cam slightly and loose your timing, so care is needed.
Repeat for the other bank.
I've seen it done that way successfully too, but rather than just stick the hose in the plug hole modify an old spark plug to screw in with the hose through it, simples.As soon as you see the shrinking make a mark on the AC pulley (I use a home made pointer bolted to the washer bottle bracket as a reference mark) This gives you a rough TDC. To get the accurate position I keep turning and when I am nearly at the rough mark, I wipe and re-dip the tube. This gives a much smaller bubble that is far easier to see when it stops growing. Mark again with a scribe for your accurate TDC mark.
It may take a few tries to get the hang of this, but when you do it is as accurate as a dead stop or dial gauge. The longer the lever you have on the crank pulley - the easier it is to make the very fine movements you need to hit exactly TDC.
If you have a thin bore tube with the soap film just over the end - you can see the film moving very accurately indeed - to within a fraction of a degree.
Once you have TDC for the front cylinder on each bank marked, you want to set the cam timing to equal lift on valve overlap at TDC.
Turn the cam so that the followers on cylinder 1 (or 8 - they are 180 apart) are under the cam lobes (one is closing the other opening) and adjust so that they are exactly level. Put the cam pulley back on and tighten the timing chain, then adjust the crank to your TDC mark (with the cam pulley slipping on the shaft). Once you have them lined up you should be able to get the top 2 bolts in (with loctite!!) then turn the crank so the cam turns 180 to get the other two bolts in.
Having just done this job - I found that if you try to over tighten the first cam pulley bolts it is possible to shift the cam slightly and loose your timing, so care is needed.
Repeat for the other bank.
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