302 timing problem

cobracosta · #1 (**permalink**) 03-30-2013, 05:02 PM

I have had this kit for 10 yrs and it was a basket case when I first bought it ( it still is). My story is I usually have no time or no money and never the enough at the same time. The original owner literally threw this kit together but I wont go into all the issues. the engine has always run hot and at idle is very lumpy. The builder decided to run dual carbs and a large nitrous kit. (I never use the nitrous) I have always assumed it has an aftermarket cam and when setting timing it will not run between 12'-14' BTDC. It seems to like 20' btdc. I had a hydraulic valve go out so I replaced them all. Once I buttoned everything back up I was setting the timing and again it likes 20" btdc. In looking at the distributor the vacumn advance it turned so much Counter clockwise it is pushed against the carb spring bracket. I looked at how the spark plug wires are on the distributor and it all seems right. So the question is if you have an aftermarket cam would that cause you to retard your timing more ( from 12' btdc to 20'btdc). Im almost thinking I need a new distributor or my Harmonic balancer isnt accurate?

blykins · #2 (**permalink**) 03-30-2013, 05:23 PM

Very possible that the balancer could be off. SOP when I assemble an engine is to check the balancer marks against a degree wheel. With a lot of aftermarket SBF balancers having 2-3 sets of marks on them, it would be very easy to mess it up.

Dwight · #3 (**permalink**) 03-30-2013, 05:36 PM

buy or make a piston stop and check you 0 degree mark on the balancer. A lot of timing markers are installed incorrectly and the damper could have slipped or is marked wrong.

Dwight

cobracosta · #4 (**permalink**) 03-30-2013, 05:56 PM

will do. thx for the help.

Dwight · #5 (**permalink**) 03-31-2013, 07:17 AM

If you ready what to get crazy about timing, check your distributor cap and rotor for correct phasing.
This will require an old cap that you can cut a window into so you can look at the plug button to rotor tip gap.
I know this will be hard to believe but sometime they manufacture bad rotors and caps!!

Dwight

zrayr · #6 (**permalink**) 03-31-2013, 07:35 AM

Quote:

Originally Posted by cobracosta

"..........So the question is if you have an aftermarket cam would that cause you to retard your timing more ( from 12' btdc to 20'btdc)..........."[/img][/url]

when going from 12 degrees BTDC to 20 degrees BTDC you are advancing your timing, not retarding it.

terminology aside, yes. A cam with more duration will generally need more timing (advanced) to completely burn the intake mixture, especially at idle

Z.

olddog · #7 (**permalink**) 03-31-2013, 08:09 AM

A Cam with a lot of valve overlap will idle with less manifold vacuum. You may need to adjust or change out the vacuum canister. The Vacuum advance should pull in 20 degrees of advance at idle. It should be pulled in solid at about 1 "Hg less than the engine idles. If not the idle is going hunt all over the place, because rpm changes vacuum, vacuum changes advance, and advance changes rpm. It will chase its tail.

You set the timing with the vacuum disconnected and plugged. Then when you plug it in you should see the timing advance 20 deg and it should be very stable.

vector1 · #8 (**permalink**) 03-31-2013, 08:17 AM

advancing the timing should make it run smoother. disconnect the vacuum advance until you get everything lined out.

cobracosta · #9 (**permalink**) 03-31-2013, 10:49 AM

I did have the vacumn advance disconnected when I was trying to time it. The engine idles well at 20' but has almost no power. I'm thinking I need to get the engine stop and see if the timing mark is accurate. Also I would like to buy a new distributor.

cobracosta · #10 (**permalink**) 04-04-2013, 05:17 PM

well I used a piston stop and the Harmonic balancer is at TDC. it must be something in the distributor. Im going to double check that all cylinders are firing as well.

Wbulk · #11 (**permalink**) 04-04-2013, 08:13 PM

Cobracosta, read this thread, Dist. Advance Re-curve

It sounds like you may have a problem with your distributor. Take the cap off try and turn the rotor counter clockwise by hand. It should turn about 3/8" or so and when you let go return back to the stops. When you let go see if you can turn it clockwise. If you can it's not returning to O and is hanging up.

One other thing, could this engine have a 351 cam in it? The firing order is differant.

cobracosta · #12 (**permalink**) 04-07-2013, 02:33 PM

Ill have to check the distributor..... I have to do a search for valve adjustment. I went and did a comp check to see if maybe the valves werent closing and I think that may be part of it. when I adjust the rockerarm so you can barely spin it and then tighten a 3/4 turn I think it is too much and leaving the valve open. something is not right.

olddog · #13 (**permalink**) 04-07-2013, 06:27 PM

Quote:

Originally Posted by cobracosta

when I adjust the rockerarm so you can barely spin it and then tighten a 3/4 turn I think it is too much and leaving the valve open.

It is very possible you are compressing the lifter as you are getting it to the point where you cannot spin it. The starting point should be where things are touching with no slop, but the lifter is not compressed at all (fully pumped up). Depending on your strength you may be starting with the lifter partially compressed.

Your positive it is a hydraulic lifter aren't you?

cobracosta · #14 (**permalink**) 04-08-2013, 05:15 PM

yep I just replaced them

I think I should not do the extra 3/4 turn once I get the pushrod w/o slop. I noticed when I was replacing the lifters they were all original mighty loose. you could wiggle the rockerarm....... I was thinking of doing a leak down test after I adjust the valves to see if its the valve partially open. I have a compression tester not sure i Have the attachment to put compressed air in the cylinder though.

cobracosta · #15 (**permalink**) 04-14-2013, 05:47 PM

ok I readjusted the valves, I dont have roller rockers so I tried to adjust how the chilton book said with a feeler gauge..... I cant fit a feeler gauge due to 2 ridges on either side of the valve tip. I adjust so there was just no movement of the pushrod. everything seems to be working now. was able to time to 16'. its very lumpy but I think I have Carb issues. I'm going to rebuild and see how lean I can get the two carbs to go. I really would like to go down to one carb.