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Can anybody here help me out on finding top dead center on the HT4100?

The car is an 1987 FWD Fleetwood Deville with 137,000 miles on it. My little brother bought it a couple weeks ago but it needs the distributor assembly replaced. The former owner tried to fix it himself by replacing it with a new one but messed up and turned it over after forgetting to tighten the distributor bolt and gave up on it. We know it runs as we know the previous owner, but I have no clue on how to find TDC on this motor and he does not have a manual for it as of yet. We can't see a mark on the crank pulley so are wondering if there is a specific position a piston should be in and how we could tell where it was.

Thank you in advance for your input.

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Typically, TDC is when the number 1 cylinder is at the top of its compression stroke, and both valves are closed.

Mark the number 1 tower position from the distributor cap on the frame of the distributor. At that point, I would line up the contactor on the rotor with the mark you put on the distributor frame distributor, that will give a rough starting point, then I would fine time it with a timing light as detailed in the manual.

I stand corrected if I am wrong

I don't know which cylinder is #1, but I believe the firing order is 1,8,4,3,6,5,7,2 and you should be able to find #1 using that, check the intake for a verification of the firing order

Pre-1995 - DTC codes OBD1  >>

1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm

How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/

Cadillac History & Specifications Year by Year  http://www.motorera.com/cadillac/index.htm

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I had a 1984 HT 4100.

Mike is right... the firing order is stamped on the intake.

I think the intake is also "STAMPED" with a number "1" to show you which cylinder number "1" is.

Look on the crankshaft pulley again for markings.

It "SHOULD" be marked.

One way to tell top dead center... pull number one plug...put a broom straw in the hole...pointing down towards the top of the piston.

Bump the starter... a little at a time...till the straw quits rising...if it starts back down... you passed TDC.

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Thanks for the quick response, I have limited experience with the old distributors except for when I replaced the cap and rotor on my old Caddy, so it's difficult trying to help him out on this one.

Might be a stupid question though, but is there a way tell if the piston is on the compression stroke and not between the exhaust and the intake strokes? Just wondering if there is a trick to the trade here without removal of the intake or exhaust manifold on the front end for Cyl #1. I have a small pipe camera I can drop through the spark plug hole, but that will only let me know when the piston is at the top of the combustion chamber which could either be in the compression stroke, or between the exhaust and intake strokes.

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With the spark plug "REMOVED"... stick the end of your finger in the hole.

Bump the starter again.

When it comes up on compression stroke... the pressure will push against your finger.

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You can also use a breaker bar and socket in the balancer pulley bolt to rotate the engine. Look for the timing mark on the balancer pulley - when the timing mark on the balancer pulley is lined up with the marks on the block, you will be very close. Use a wood dowel in the no. 1 spark plug hole to monitor the movement and get it exactly at top dead center.

It has been so long since I worked on a HT-4100, I forgot what cylinder is no. 1.

Kevin
'93 Fleetwood Brougham
'05 Deville
'04 Deville
2013 Silverado Z71

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Good news! The thing is running now, has a bit of a high idle but the TPS seems to be making a bit of a grinding noise so he'll try replacing that as the car id presenting no current codes and unrelated history codes.

He took the FR wheel off to get at the front of the engine with some engine brite and a pressure washer and couldn't find any marks on the pulley (aftermarket we assume) so we followed the advice of everyone here and brought this beauty to life again.

Thank you everyone for being such a great help.

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  • 1 year later...

Good news! The thing is running now, has a bit of a high idle but the TPS seems to be making a bit of a grinding noise so he'll try replacing that as the car id presenting no current codes and unrelated history codes.

He took the FR wheel off to get at the front of the engine with some engine brite and a pressure washer and couldn't find any marks on the pulley (aftermarket we assume) so we followed the advice of everyone here and brought this beauty to life again.

Thank you everyone for being such a great help.

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