351W Build, No compression?!

hoss · 10-07-2007

Hey 351W experts...

My buddy is building a 351W for his truck, and we went to fire it up for the first time, and we are getting no compression. Seems to be blowing air out of the intake, and kinda sucking in thru the exhaust (MAYBE?) Quick specs

1974 351W (from a Gran Torino)
Heads from a 302 (from a nice running 1984 lincoln towncar)
Stock bottom end (we replaced the bearings and checked clearances)
Cheap ass "4x4 offroad cam" & lifter set (Summint Racing brand)
Edelbrock intake & carb
headers and flowmasters (last two don't really matter)

I wish i had cam numbers, but i don't think it came with any anyway.

to time the cam, all we did was align the mark on the crank sprocket with the middle mark on the cam sprocket. all valve events seem to be occur at the right time in the stokes (not obviously 180deg off or anything) compression guage yeilds nothing. FLAT ZERO! with #1 @ TDC and both rockers loose, a leakdown test shows some airflow from both intake and exhaust. the head donor ran GREAT, which is why i don't think the valves are leaking bad enought to cause 0psi of compression. with your finger over the plug hole it seems to suck (create a vacuum) rather than blow your finger off during cranking.

I hope it is something simple I am overlooking, but we're stumped at this point. Hopefully someone here can point me in the right direction.

Thanks so much!

-Hoss-

hotwheels · 10-07-2007

Check the rocker adjustments again and make sure they are set right......Then i would check to make sure my timing chain is on correctly, i have seen people try to use those fancy ones and get them off just enough to cause the problem you are describing.....

DARKHORSE · 10-07-2007

Quote:

to time the cam, all we did was align the mark on the crank sprocket with the middle mark on the cam sprocket. all valve events seem to be occur at the right time in the stokes (not obviously 180deg off or anything) compression guage yeilds nothing. FLAT ZERO! with #1 @ TDC and both rockers loose, a leakdown test shows some airflow from both intake and exhaust. the head donor ran GREAT, which is why i don't think the valves are leaking bad enought to cause 0psi of compression. with your finger over the plug hole it seems to suck (create a vacuum) rather than blow your finger off during cranking.

run that same test with rockers off the head

DARKHORSE · 10-07-2007

i have seen people try to use those fancy ones and get them off just enough to cause the problem you are describing.....

so true..........

Intmdtr · 10-07-2007

is the cam lobes to tall for the valves? sounds like they are not seating properly.....just another angle. i had a prob like that years ago, tried to go wild on the cam but with a set of stock heads just didn't cut it.

Justafordguy · 10-07-2007

I would say it's cam timing or the push rods are too long.

hoss · 10-08-2007

Thanks guys! we pulled the front end off and found out that the 2 guys that put the timing chain on had it WAY off. I was kind of suspicious while it was still on the stand, but my buddies insisted they had it right. got the cam in time and we have compression now! I knew it couldn't be anything too horrible. We'll have to see how she runs...

Thanks again guys!

-Hoss-

hotwheels · 10-08-2007

Right on man.........

Intmdtr · 10-08-2007

good to hear ya figured it out

10-07-2007	#1 (permalink)
hoss Hillbilly on the Hill Join Date: Apr 2007 Location: Michigan Posts: 161 iTrader: (1) Friends: (5) Last Online: 09-29-2011 07:27 PM Time Spent Online: 7 Hours 50 Minutes 32 Seconds My Album's: hoss's album My Garage: hoss's Garage Thanks: 0 Thanked 1 Time in 1 Post	351W Build, No compression?! Hey 351W experts... My buddy is building a 351W for his truck, and we went to fire it up for the first time, and we are getting no compression. Seems to be blowing air out of the intake, and kinda sucking in thru the exhaust (MAYBE?) Quick specs 1974 351W (from a Gran Torino) Heads from a 302 (from a nice running 1984 lincoln towncar) Stock bottom end (we replaced the bearings and checked clearances) Cheap ass "4x4 offroad cam" & lifter set (Summint Racing brand) Edelbrock intake & carb headers and flowmasters (last two don't really matter) I wish i had cam numbers, but i don't think it came with any anyway. to time the cam, all we did was align the mark on the crank sprocket with the middle mark on the cam sprocket. all valve events seem to be occur at the right time in the stokes (not obviously 180deg off or anything) compression guage yeilds nothing. FLAT ZERO! with #1 @ TDC and both rockers loose, a leakdown test shows some airflow from both intake and exhaust. the head donor ran GREAT, which is why i don't think the valves are leaking bad enought to cause 0psi of compression. with your finger over the plug hole it seems to suck (create a vacuum) rather than blow your finger off during cranking. I hope it is something simple I am overlooking, but we're stumped at this point. Hopefully someone here can point me in the right direction. Thanks so much! -Hoss- __________________ 78 Granada: Explorer 5.0 EFI, C-4, 8.8 (3.73 L/S Disc)... 93 CBR600: Two Brothers Pipe, Jetted, -1/+3 gearing, awaiting '05 body conversion... 96 F250HD: 7.3L Powerstroke, ZF5, Valair 900ft/lb clutch, DIY Tymar intake, 3" MBRP downpipe, 4" back to dual 5" stacks, BB FPR Shim, DIY HPOP pressure fooler... Sticks and tunes to come... Daily Driver...

10-07-2007	#2 (permalink)
hotwheels Car Enthusiast Real Name: Doug Join Date: Aug 2006 Location: Cheyenne, Wyoming Posts: 21,165 MySpace ID: insanemustangs_com Facebook ID: Insanemustang Mustangs Twitter ID: insanemustangs iTrader: (0) Friends: (416) Last Online: 1 Day Ago 07:58 AM Time Spent Online: 3 Weeks 6 Days 6 Hours 31 Minutes 32 Seconds My Album's: hotwheels's album My Garage: hotwheels's Garage Thanks: 3 Thanked 40 Times in 39 Posts	Check the rocker adjustments again and make sure they are set right......Then i would check to make sure my timing chain is on correctly, i have seen people try to use those fancy ones and get them off just enough to cause the problem you are describing..... __________________ Webmaster in training and owner of a mini Jay Leno Poorman's car collection

10-07-2007	#5 (permalink)
Intmdtr Leader of Men Real Name: Brian Join Date: May 2007 Location: Wasaga Beach, Ontario Posts: 9,312 iTrader: (1) Friends: (34) Last Online: 13 Hours Ago 04:59 PM Time Spent Online: 2 Weeks 5 Days 21 Minutes 54 Seconds My Album's: Intmdtr's album My Garage: Intmdtr's Garage Thanks: 1 Thanked 29 Times in 28 Posts	is the cam lobes to tall for the valves? sounds like they are not seating properly.....just another angle. i had a prob like that years ago, tried to go wild on the cam but with a set of stock heads just didn't cut it. __________________ HELLO My Name is BRIAN "Without Warning, Without Conscience" *"Live life to the fullest, it's not a dress rehearsal"*

10-07-2007	#6 (permalink)
Justafordguy Just Insane Real Name: Gary Join Date: Aug 2006 Posts: 236 iTrader: (0) Friends: (1) Last Online: 13 Hours Ago 04:43 PM Time Spent Online: 2 Days 11 Hours 3 Minutes 47 Seconds My Album's: Justafordguy's album My Garage: Justafordguy's Garage Thanks: 0 Thanked 0 Times in 0 Posts	I would say it's cam timing or the push rods are too long. __________________ 80 Hatch, 351W, built C4, 2600 Stall 70 Coupe, 351W, Auto, PS, PDB, AC 77 Bronco, 302, Auto, PS, PDB 05 F-250, 6.0 PSD, 5-speed Auto, 4x4 CrewCab

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10-07-2007	#4 (permalink)
DARKHORSE Super Moderator Join Date: Aug 2006 Location: cheyenne Posts: 903 iTrader: (0) Friends: (6) Last Online: 2 Days Ago 12:30 AM Time Spent Online: 2 Days 5 Hours 22 Minutes 45 Seconds My Album's: DARKHORSE's album Thanks: 0 Thanked 0 Times in 0 Posts	i have seen people try to use those fancy ones and get them off just enough to cause the problem you are describing..... so true..........

10-08-2007	#7 (permalink)
hoss Hillbilly on the Hill Join Date: Apr 2007 Location: Michigan Posts: 161 iTrader: (1) Friends: (5) Last Online: 09-29-2011 07:27 PM Time Spent Online: 7 Hours 50 Minutes 32 Seconds My Album's: hoss's album My Garage: hoss's Garage Thanks: 0 Thanked 1 Time in 1 Post	Thanks guys! we pulled the front end off and found out that the 2 guys that put the timing chain on had it WAY off. I was kind of suspicious while it was still on the stand, but my buddies insisted they had it right. got the cam in time and we have compression now! I knew it couldn't be anything too horrible. We'll have to see how she runs... Thanks again guys! -Hoss-

10-08-2007	#8 (permalink)
hotwheels Car Enthusiast Real Name: Doug Join Date: Aug 2006 Location: Cheyenne, Wyoming Posts: 21,165 MySpace ID: insanemustangs_com Facebook ID: Insanemustang Mustangs Twitter ID: insanemustangs iTrader: (0) Friends: (416) Last Online: 1 Day Ago 07:58 AM Time Spent Online: 3 Weeks 6 Days 6 Hours 31 Minutes 32 Seconds My Album's: hotwheels's album My Garage: hotwheels's Garage Thanks: 3 Thanked 40 Times in 39 Posts	Right on man.........

10-08-2007	#9 (permalink)
Intmdtr Leader of Men Real Name: Brian Join Date: May 2007 Location: Wasaga Beach, Ontario Posts: 9,312 iTrader: (1) Friends: (34) Last Online: 13 Hours Ago 04:59 PM Time Spent Online: 2 Weeks 5 Days 21 Minutes 54 Seconds My Album's: Intmdtr's album My Garage: Intmdtr's Garage Thanks: 1 Thanked 29 Times in 28 Posts	good to hear ya figured it out

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