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i suspect the timing mark on my harmonic balancer is not accurate i would like some input as to determine the correct location on the balancer. the method i used was to hold my finger over the plug hole and watch for full compression and taking note of the marks location. it seems to be at the top of the plate about 16 degrees off. is there a way to more accuratly determine this. i am reluctant to use a wire rod to follow the piston as when i tried i found it hard to follow as they are not flat top pistons. it is a L72, i suspect this to be the cause of my stumbling issue as advancing the timing corrects it. bill
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Re: timing mark off?
Bill
I check the TDC mark as follows.
1. disconnect the battery. Never use the starter for this procedure.
2. remove #1 sparkplug and rotate engine by hand until you are near BDC for #1.
(It may be easier turning the engine if all spark plugs are removed)
3. Insert piston stop into sparkplug #1. and rotate engine backwards until the piston meets the stop. Do not force. I made a piston stop out of an old spark plug.
4. Place a 4” piece of masking tape on the edge balancer and rig a pointer and make a mark on the tape. I like to use the top end of the timing tab as the pointer.
5. Now rotate the engine forward until the piston again meets the stop. Make a second mark at the pointer and find the center between the two marks and mark it. I use a pair of dividers to find the center.
6. Remove the piston stop. And rotate the engine until the center mark is lined up with your pointer mark. If the balancer has no error, the timing marks should be lined up on TDC. If there is error it can be easily compensated for when timing the engine.
For example if the timing mark is 2 deg advances, add the error to the base timing.
Example: base timing is 6 deg plus 2 deg error make base timing 8 deg. If retarded subtract the error.
Good luck
BV. -
Re: can you explain piston stop?
can you tell me what a piston stop is? i cannot quite picture it, billComment
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Crank keyway lines up with timing mark
On BB Chevy, the crank keyway lines up with the mark. Remove the lower pulley and the big bolt/washer from the center of the crank and the answer will be obvious.
Good Luck,
MarkComment
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Re: can you explain piston stop?
Bill,
A piston stop is a simple depth gauge device that threads into the spark plug hole. It provides an accurate reading of piston TDC without fear of damage or scoring by poking a wire or having a pencil break off inside the cylinder. They are cheap to buy and may even be available for loan at places like NAPA and Autozone.
For reference Summit Racing has several. Here is a link to one:
Take your time...you waited this long!
MikeComment
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Re: can you explain piston stop?
Try this link instead. If this doesn't work just search on "piston stop"
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Re:what thread size do i have?
on the 858 heads?Comment
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Re:easy wait!
we have 12 inches of snow on the ground. unbelievable! more coming. this a been a long winter in vermont.Comment
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Re:what thread size do i have?
I'm 99.99% sure it's 14mm. Do you have a caliper handy? It will tell you close enough compared to 18mm.Comment
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Re:easy wait!
Bill, I'm over here in NH. The lawn is white again. This is really getting on my nerves.
HarryComment
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Re:what thread size do i have?
Bill,
What plugs are you running? If they are delco 44, 45, etc. or a different make's equivalent plug, then you have 14mm threads. The 4 in R45 represents 14mm, and the 5 is the heat range.
JoelComment
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GM sells a nice piston stop part# 12364087
you need one with a hole in it so the compression can come out easily as you turn the engine overComment
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Re: GM sells a nice piston stop...12364087
You can't beat the price...$9.09 through GMPartsHouse.com. Of course, the shipping will probably be more than half the price.
GMPartsHouseComment
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Re: GM sells a nice piston stop...12364087
$8.01 at GM parts Direct
http://www.gmpartsdirect.com/results.cfmComment
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A Good Example Of...
Why GMPartsDirect Never Gets Any Orders From Me...I always compare SHIPPED prices when buying parts on the internet. GMPartsDirect shipping/handling charge for 12364097 is $9.95! Final shipped prices: GMPartsHouse = $17.04; GMPartsDirect = $17.96
In fact, if you're willing to wait a week or so, always compare internet shipped prices with the price your local dealer quotes. In this case, you can probably save money by buying at the dealer...GM list price is only $11.00 FOB his parts counter (assumes the "gouge" is not in). Of course, internet orders are delivered to your door, and you'll have to drive down to your dealer at least twice to get it...six of one, half dozen of the other.Comment
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