Timing Belt/Timing Mark Problem!
08-04-2002 | 02:47 AM
#1
Thread Starter
Three Wheelin'
Joined: Jun 2001
Posts: 1,598
Likes: 0
From: San Jose, CA
Timing Belt/Timing Mark Problem!
So, I installed the new timing belt and balancer belt...made sure all the perty marks aligned, then tried to make a couple of turns on the crank to make sure nothing was contacting anything..."clunk". Doh! Looks like the crank got turned somehow during his operation(i didn't use the flywheel lock).
At this point can i just pull the timing belt off and rotate the crank until i see the mark again...then install the timing belt making sure that the cam mark is aligned?
At this point can i just pull the timing belt off and rotate the crank until i see the mark again...then install the timing belt making sure that the cam mark is aligned?
08-04-2002 | 04:18 AM
#2
Race Car
Joined: Jun 2002
Posts: 3,781
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From: Costa Mesa, California
Well yes and no.
With the 1st cylinder a bit down from TDC I think the other three are also sufficiently shy of the top of the block that you can rotate the cam with out more than fighting the valve spring pressure. Remember that every time number one cylinder is TDC the timing mark on the flywheel is in the view port above the two speed sensors.
So take out the spark plugs and get a wood dowel and probe the #1 cylinder as you turn the crank the direction that takes the piston toward the head. By making marks on the dowel you should be able to check that the other three pistons are shy of the top of their stroke too.
What you want is the cam gear mark lining up with the notch on the housing behind it. Then rotate the crank to bring #1 piston to TDC in the shortest movement possible. Use the dowel and the mark on the flywheel to get it right.
I've found that rotating the cam a bit clock wise, slipping the belt on the cam gear and turning the cam counter clock wise to tighten the belt between it and the crank pulley then checking the marks gets it right the first time -- no skipped teeth.
If you find the cam hanging up with #1 piston a bit toward mid stroke try turning the crank a bit either way then try turning the cam again.
Note this is for the 8 valve NA 944 engine.
With the 1st cylinder a bit down from TDC I think the other three are also sufficiently shy of the top of the block that you can rotate the cam with out more than fighting the valve spring pressure. Remember that every time number one cylinder is TDC the timing mark on the flywheel is in the view port above the two speed sensors.
So take out the spark plugs and get a wood dowel and probe the #1 cylinder as you turn the crank the direction that takes the piston toward the head. By making marks on the dowel you should be able to check that the other three pistons are shy of the top of their stroke too.
What you want is the cam gear mark lining up with the notch on the housing behind it. Then rotate the crank to bring #1 piston to TDC in the shortest movement possible. Use the dowel and the mark on the flywheel to get it right.
I've found that rotating the cam a bit clock wise, slipping the belt on the cam gear and turning the cam counter clock wise to tighten the belt between it and the crank pulley then checking the marks gets it right the first time -- no skipped teeth.
If you find the cam hanging up with #1 piston a bit toward mid stroke try turning the crank a bit either way then try turning the cam again.
Note this is for the 8 valve NA 944 engine.
08-04-2002 | 03:46 PM
#3
Racer
Joined: Apr 2002
Posts: 424
Likes: 0
From: Denver Colorado
The first time I changed the timming belt and balance shaft belt I also rotated the crank and heard a "clunk" as it turned out the clunk was the bending of valves. I hope this is not your case. I would reccommend doing a compression test after you are done to make sure everything is ok.
08-05-2002 | 02:57 AM
#4
Racer
Joined: Mar 2002
Posts: 293
Likes: 0
From: San Jose
Mike,
I thought I did the same thing when I was replacing the belts and and I didn't use the flywheel lock. I would recommend using the flywheel lock for sure next time for peace of mind.
I'm still waiting for parts to come in before fully assembling the front-end, but I'm going to do a leak-down test afterwards to check for bent valves. This is the only way to make sure if the valves are bent or not. A compression check will not fully reveal a slightly bent valve since it's checking for maximum pressure.
What was recommended to me from a previous post was to rotate the cylinders until they are half-way up (i.e. all pistons are at equal height -> this should be 1/4 crankshaft revolution from TDC). Then rotate the camshaft to TDC for each of the cylinders to close the valves for those respective cylinders. Do a leak-down test for each cylinder while it's at TDC for that cylinder. All this assumes that the belts are off and you can move the camshaft and crankshaft independently.
BTW, you can make your own leak-down tester and not have to pay the $50 or $100 for what the stores want to charge for this tool. Cost me about $25 to piece the whole thing together. Most parts I got from Home Depot (brass nipples, T and pneumatic quick connects) and regulator and gauge from Harbour Freight ($10 for regulator and $6 for gauge, 2 most expensive pieces). I used the hose from a compression checker I had to couple to the leak-down tester. You have to remove the Schrader valve in the compression checker hose to make it work correctly otherwise you'll always read no-leak condition.
Hope this helps.
*****
I thought I did the same thing when I was replacing the belts and and I didn't use the flywheel lock. I would recommend using the flywheel lock for sure next time for peace of mind.
I'm still waiting for parts to come in before fully assembling the front-end, but I'm going to do a leak-down test afterwards to check for bent valves. This is the only way to make sure if the valves are bent or not. A compression check will not fully reveal a slightly bent valve since it's checking for maximum pressure.
What was recommended to me from a previous post was to rotate the cylinders until they are half-way up (i.e. all pistons are at equal height -> this should be 1/4 crankshaft revolution from TDC). Then rotate the camshaft to TDC for each of the cylinders to close the valves for those respective cylinders. Do a leak-down test for each cylinder while it's at TDC for that cylinder. All this assumes that the belts are off and you can move the camshaft and crankshaft independently.
BTW, you can make your own leak-down tester and not have to pay the $50 or $100 for what the stores want to charge for this tool. Cost me about $25 to piece the whole thing together. Most parts I got from Home Depot (brass nipples, T and pneumatic quick connects) and regulator and gauge from Harbour Freight ($10 for regulator and $6 for gauge, 2 most expensive pieces). I used the hose from a compression checker I had to couple to the leak-down tester. You have to remove the Schrader valve in the compression checker hose to make it work correctly otherwise you'll always read no-leak condition.
Hope this helps.
*****
08-05-2002 | 01:27 PM
#5
Thread Starter
Three Wheelin'
Joined: Jun 2001
Posts: 1,598
Likes: 0
From: San Jose, CA
Thanks for the advice guys. I got her all back together and timed correctly this time. I was turning really slowly when i heard had contact, it was more of a tap and stop of motion. I doubt that i hurt the valves, but i'll give it a check after she's all back together(waiting for plug wires and other miscellaneous parts). I'll definitely be investing in a flywheel lock next time though...for $30, it isn't worth the hassle to not have one.
