472 TUNRS OVER SLOW

[honeymonster]

HI GUYS GOT A SMALL PROBLEM
IVE GOT A 472 MATED TO A TH400 WITH THE PLUGS IN IT TURNS OVER VERY SLOW TAKE THEM OUT SPINS EASY COMPRESSION TEST SHOWS NO1 AT 180 NO 3 AT 156 NO5 AT 166 NO 7 141 NO 2 AT 156 NO 4 AT 159 NO 6 AT150 NO 8 AT 148 PSI GOT GOOD OIL PRESSURE ENY SUGGESTIONS PLEASE GUYS THANKS HONEYMONSTER :twisted:

[Nashalac]

Battery, battery connections, battery cables, starter, starter connections, engine ground. Sounds like a voltage problem or starter/battery.

[honeymonster]

TESTED ALL CONECTIONS EVEN WITH BOOSTER BATTERY ON STILL SLOW ARE THE COMPESION TESTS ALRIGHT OR IS IT WORTH INVESTING IN A HIGH TOQUE STARTER THANKS HONEYMONSTER :twisted:

[Nashalac]

Compression does not appear to be the problem

[STDog]

HI GUYS GOT A SMALL PROBLEM
IVE GOT A 472 MATED TO A TH400
What compression ratio? Is it a high compression from 68-70, or one of the 8.5:1 engines?
They both list the same starter, but the high compression engine will turn noticably slower.


#1 @ 180
#3 @ 156
#5 @ 166
#7 @ 141
#2 @ 156
#4 @ 159
#6 @ 150
#8 @ 148

#1 looks kind of high compared to the others. 157 is the average, so #1 is 23 psi higher, nearly 15% above the average. #7 is low by 16 psi, or 10% below average.
you might have some problems on those cylinders.

I'm not sure what the average should be, nor the range, but 10% seams high.
What's the history on the engine? Have you had the starter tested? How old is it, was it new or rebuilt, by whom?

I'd still check the wire from the battery to the starter. It get's hot, and becomes resistive. Try a multimeter with pos at the battery(+) and neg at the starter. What's the voltage drop across the cable? Try the same with post on the starter housing and neg on the battery(-). What's the voltage there? Both should be nearly zero.

[STDog]

Compression does not appear to be the problem
What's the variation supposed to be? 15% sound high to me.

[Nashalac]

Although the compression does vary quite a bit I don't think that is the CRANKING problem. May have other issues with the engine but the voltage drop tests should at least ck the wiring. That is an excellent test most people never do.

[STDog]

Although the compression does vary quite a bit I don't think that is the CRANKING problem.
Yaeh, different problem. But still probably should be looked into.

but the voltage drop tests should at least ck the wiring. That is an excellent test most people never do.
All those years to get my BSEE were not wasted :)
First place I look with any starter problems.

[Terrible One]

Still sounds like the starter to me.

[DV8]

Checking for voltage isn't enough, IMO.

You need to remove ALL connections and clean them with some sandpaper. Get a ternimal scraper if you are top-post. These things will not show up with a test light or visual inspection.

I've saved lots of $ with my $2 battery terminal scraper - batteries that were still fine and starters that didn't have anything wrong with them....

DV8

[STDog]

Checking for voltage isn't enough, IMO.

I wasn't talking about test lights or visuals. The voltage drop on the wire will show you bad wires and bad connections. Put the pos probe on the battert, not the connectior, but on the post. Then put the neg probe on the brass stud on the starter. Tht will tell you if there's an resistance in between.

On the ground side, you put the pos probe on the starter housing, and the neg probe on the battery post. Again you 'll fid and resistivity in the return path.

I fogot to mention, you need to measure the voltage drop with the starter turning. Without current flow there won't be a voltage drop.

I'd have to check the current draw on the starter, but I would expect less that 0.1 V on the return pathe, and less that 0.2V on the supply. Rember how close to the exhaust the battery cable runs. It gets very hot, and increases the wire's resistance. I've seen the wire get very resistive, while the cable looked fine. Not hot enough to deform the insulation, but it affected the wire in the cable.

I agree something is probably wrong. Measuring the voltage drop is the easiest and fastest check. If you have a clip on ammeter, you cna chek the starter's current draw, which is another good check. Any other testing required removal of the starter, and taking it somwhere that can test the starter with a load. Most place will just check the unloaded current draw, which might miss something. A torque test would be good too.

You need to remove ALL connections and clean them with some sandpaper
That includes all the ground connections! Thus removin the starter and cleaning the block and starter where they mate. And the ground strap that's probably connected to the bell housing. Don't for get where that strap connect to the frme, and where the ground cable for the battery connect to the frame.

I had trouble when I got my car. Somone mounted a cut off switch under the dash in the return path. So a 4ga wire ran from the batter to the switch under the dash, and another to a bolt under the dash. Way too much resistance in the return path, so the start was slow.

The stock starter for the engine should have no trouble with even a 10.5:1 engine. High torque, 3rd party starters are only usefull for weight savings, or real high compression (dynamic or static) engines.

[Nashalac]

What STDog said. Most people don't understand what a voltage drop test is/does. It WILL check connections and wiring for any poor connections or bad wiring.

[DV8]

Amen, brothers!

I just wanted to make sure that nobody out there considered a test light a good enough check for voltage. You guys explained it to a "T".....

DV8

[Fordalac13]

I vote for to much starter drag(internal) :roll: my 2 cents. Jerry

[STDog]

I vote for to much starter drag(internal) :roll: my 2 cents. Jerry

Which would be detctable by testing the current draw under a load.
I don't think a no-load test would catch it, but it might.

[Nashalac]

Or you could just start relacing all the parts and hope it isn't something between the parts. Just buy it all!!

[honeymonster]

hi guys thanks for all the replies it was a combination of bad connections on earth side plus dirty brushes in starter thanks honeymonster :twisted: