How not to install cams
02-20-2004, 08:43 AM
#1
Drifting
Thread Starter
How not to install cams
The cams were installed at the weekend at 45BTDC and yesterday I managed to do a dry run on installing the cam belt. It was only a dry run because I hadn't yet received the Loctite 574 so the cam towers couldn't be installed. Once the cam sprockets were on I lined them up with the 45BTDC marks that I'd already added and put the belt on. Then I turned the crank carefully through 90 degrees at which point the TDC marks were aligned on the cam sprockets.
At this point I thought I'd better put the harmonic balancer back in place too, and as I did I saw that the crank was NOW at 45BTDC!!! Somehow I had managed to convince myself that the crank was at 45BTDC when I installed the cams when it was actually 90 degrees before that. I've spent several months getting to this stage and I could now feel my blood freeze as I realised I might have ruined everything.
Installing the cams with the crank exactly 90 degrees out was not in itself going to damage anything (as long as they were immediately removed) as there must be four crank positions where you can spin the cams without physical contact. However turning the crank through 90 degrees with the belt installed would bring two pistons through the top of their stroke. The question in my mind was obviously had any of the valves in either of those cylinders been open as the pistons moved.
I didn't have much time to think about it as the daylight was now fading and I had to pack up, but I have thought about it a lot since. I don't think I have caused any damage for the following reason. The car has S4 cams which have 8mm lift, none of the hydraulic followers have any oil in them and so you can depress them at least 4mm by hand and the only thing that happens is that the spring in the follower compresses. I think, or at least I hope, that you can drop a valve about 4mm before it reaches the recess in the piston crown. There's maybe a 1.5mm recess in to the head, 1mm gasket, and 2mm or more recess in to the piston crown. That should account for very slightly more than the 8mm cam lift, I think or rather I hope it will be ok...
At this point I thought I'd better put the harmonic balancer back in place too, and as I did I saw that the crank was NOW at 45BTDC!!! Somehow I had managed to convince myself that the crank was at 45BTDC when I installed the cams when it was actually 90 degrees before that. I've spent several months getting to this stage and I could now feel my blood freeze as I realised I might have ruined everything.
Installing the cams with the crank exactly 90 degrees out was not in itself going to damage anything (as long as they were immediately removed) as there must be four crank positions where you can spin the cams without physical contact. However turning the crank through 90 degrees with the belt installed would bring two pistons through the top of their stroke. The question in my mind was obviously had any of the valves in either of those cylinders been open as the pistons moved.
I didn't have much time to think about it as the daylight was now fading and I had to pack up, but I have thought about it a lot since. I don't think I have caused any damage for the following reason. The car has S4 cams which have 8mm lift, none of the hydraulic followers have any oil in them and so you can depress them at least 4mm by hand and the only thing that happens is that the spring in the follower compresses. I think, or at least I hope, that you can drop a valve about 4mm before it reaches the recess in the piston crown. There's maybe a 1.5mm recess in to the head, 1mm gasket, and 2mm or more recess in to the piston crown. That should account for very slightly more than the 8mm cam lift, I think or rather I hope it will be ok...
02-20-2004, 09:14 AM
#2
Racer
Join Date: Mar 2003
Location: Columbus Ohio
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Paul,
If you didnt feel any interaction between the pistons and the valves while rotating the crank by hand you should be ok. Generally you would come to a point that the engine wouldnt rotate if they collided. Most of your major damage occurs when the engine is under power and they collide through inertia.
Hope this helps
Z
If you didnt feel any interaction between the pistons and the valves while rotating the crank by hand you should be ok. Generally you would come to a point that the engine wouldnt rotate if they collided. Most of your major damage occurs when the engine is under power and they collide through inertia.
Hope this helps
Z
02-21-2004, 04:45 PM
#3
Your probably Ok Paul, and you should have felt extra resistance when turning the engine. Worst case is that you have slightly 'tipped' some valves, but it will still run.
If you want to be sure before starting the car, then do a compression test on each cylinder first.
Adrian
If you want to be sure before starting the car, then do a compression test on each cylinder first.
Adrian
02-21-2004, 05:26 PM
#4
Drifting
Thread Starter
Thanks Z & Adrian, there was no extra resistance when turing the crank through 90 degrees, I hope I would have felt something obvious if there had been any interference.
Today after my earlier mistake I even remembered to spin the oil pump before fitting the belt until oil was coming out of the all the lifters. I had to do it by hand as there wasn't quite enough room to get my drill in to do it the lazy way.
By the end of tomorrow I'm hoping to hear it the engine run for the first time in three months, but I'll be checking for fuel leaks first, I couldn't bear to see it all go up in flames now...
Today after my earlier mistake I even remembered to spin the oil pump before fitting the belt until oil was coming out of the all the lifters. I had to do it by hand as there wasn't quite enough room to get my drill in to do it the lazy way.
By the end of tomorrow I'm hoping to hear it the engine run for the first time in three months, but I'll be checking for fuel leaks first, I couldn't bear to see it all go up in flames now...