Author Topic: compression test  (Read 5311 times)

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jholmes217

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compression test
« on: September 27, 2017, 01:06:28 PM »
How many squirts from an oil can should I shoot in the cylinder to do the "wet test" part of a compression test on a .060 428?  Engine is still smoking after eliminating the easy stuff (PCV valve now has a air/oil separator,  oil is restricted to the heads with size 62 Holley jets, intake gaskets changed and now there are no known leaks.)  Engine was rebuilt about 1500 miles and three years ago.
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

machoneman

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Re: compression test
« Reply #1 on: September 27, 2017, 01:32:21 PM »
Not much. 1/2 ounce or so should do it. I've always used lightweight 10W machine oil as it burns right off on re-start. But, use the lightest oil in the garage otherwise.

Btw, how long and far have you driven since the changes? If the insides of the exhaust pipes and mufflers took a real big shot of oil, it will take some time and mileage to burn off. Point being you may have fixed it already.
« Last Edit: September 27, 2017, 01:48:47 PM by machoneman »
Bob Maag

jholmes217

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Re: compression test
« Reply #2 on: September 27, 2017, 02:07:01 PM »
Not much. 1/2 ounce or so should do it. I've always used lightweight 10W machine oil as it burns right off on re-start. But, use the lightest oil in the garage otherwise.

Btw, how long and far have you driven since the changes? If the insides of the exhaust pipes and mufflers took a real big shot of oil, it will take some time and mileage to burn off. Point being you may have fixed it already.

About a 100 miles since I put a air/oil separator between the PCV valve and carb, and about 50 miles since switching from size 70 to size 62 jets to further restrict oil to the heads.
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

machoneman

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Re: compression test
« Reply #3 on: September 27, 2017, 04:37:16 PM »
Well....and if your compression test is good and maybe you can sneak in a leak-down test too if a bud has has a tester....that's likely not enough time or miles, especially the 50 miles on the restrictors. Unless your vacuum readings (you did take some I guess) are way low (typical FE intake gasket leaks) I'd drive it hot and hard some more and see if the smoke clears.

One other way to maybe tell if you fixes worked is to take just one more trip (with new or like new spark plugs) do some hi revs at/near WOT and shut her off and coast in somewhere....just like a drag car would. Pop 1-2 easy to get to plugs and see if insulator is clean of oil deposits, tan or light tan. Why is because the engine itself may have been fixed but oil still lurks inside the pipes and mufflers. Can't say how long it will take but a few nice long drives at highway speeds should speed things up. Short, around town trips...much longer for the clean up. 
Bob Maag

jholmes217

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Re: compression test
« Reply #4 on: September 27, 2017, 09:12:14 PM »
I actually have surprising high vacuum with a Oregon Cam similar to a Comp 280H Magnum.  It was 21 HG at idle if I remember right.
« Last Edit: September 27, 2017, 11:06:47 PM by jholmes217 »
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

427Fastback

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Re: compression test
« Reply #5 on: September 27, 2017, 10:27:39 PM »
My question would be ...When does it smoke ??.Under acceleration or deceleration.
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

jholmes217

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Re: compression test
« Reply #6 on: September 27, 2017, 11:05:10 PM »
My question would be ...When does it smoke ??.Under acceleration or deceleration.

Most noticeable to me at idle, especially after the engine has warmed up some.  Others behind me (convoy to a car show) said when I gave it some gas.
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

427Fastback

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Re: compression test
« Reply #7 on: September 28, 2017, 01:26:12 AM »
OK...your looking in the right place...My 427 with a 270S idles at 19 on the vacuum gauge...30 years ago I chased a smoking issue with my 427.It was on deceleration only.Took along time to figure it out.It can be very frustrating....
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

jholmes217

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Re: compression test
« Reply #8 on: September 28, 2017, 06:57:44 AM »
What did your end up being cause and the fix for yours?  I think I will have my wife or friend follow me in separate cars with our phones on speaker.  I can tell them when I am on the gas or decelerating, and they can tell me if it smoked at that time.
« Last Edit: September 28, 2017, 09:49:48 AM by jholmes217 »
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

427Fastback

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Re: compression test
« Reply #9 on: September 28, 2017, 10:19:05 PM »
My engine was sucking oil down 3 and four.This was around 1989/90 so I was around 30 years old.I tried 4 or 5 different intakes,half a dozen kinds of gaskets.I pulled the engine and had the decks done.I tried different gasket glues.It ran fine but was sucking oil..

I finally resolved myself to the fact that it could be the heads.I had C8 heads with CJ valves and a ton of work done to them.I found a virgin pair of heads that were untouched.Measurements said they were .030 thicker/taller on the intake side so I started all over on the heads.I took a break(3 months) and finally put the new heads on.Everything was fine...This whole ordeal spanned two years..

All of this happened/showed up after I had to redo the engine with 1500 miles on it because someone poured chop saw dust down my oil filler tube...Yes I know who it was (my jealous boss).I lost .007 off my std bores and all my exhaust valves and bearings.My std crank did not get harmed...
It was smoking from the start but it was also eating itself alive..

I still have the engine and its been very happy since I fixed it..It is wearing edelbrock heads now..Unleaded fuel pounded the crap out of my exhaust seats in 17,000 miles..
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

jholmes217

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Re: compression test
« Reply #10 on: September 29, 2017, 09:33:13 AM »
My heads were rebuilt while my engine was at the machine shop.  They are the original 428 Cobra Jet heads.  One of these days, I will take them off and pack them in oil to preserve them in case I ever have to sell, and put a set of aluminum heads on.  This is an expensive hobby, especially on a high school teacher budget.  Thanks for your replies.  I'll post the fix if/when I find it.
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

machoneman

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Re: compression test
« Reply #11 on: September 29, 2017, 09:46:46 AM »
Ya know....one thing to closely check is the plug condition after a healthy drive. Note if any show signs of oiling. Often, the plugs closest to the PVC valve's position show oil IF the engine is sucking oil past the valve (with your oil separator, not likely that's the issue). If say the other non-PCV valve side of the engine shows oiling, it's something else.

I wonder too if your shop installed exhaust valve side valve seals as some don't, thinking it's a benefit. Nope, as this is race engine stuff only. That and loose valve guides (especially if they were knurled to tighten things up since this 'fix' tends to wear out the knurling pretty quickly) will often overcome even the best intake/exhaust seals and allow excess oil. 
Bob Maag

jholmes217

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Re: compression test
« Reply #12 on: September 29, 2017, 10:18:14 AM »
All 8 plugs have been oily.  That's why I was thinking PCV and/or not enough oil restriction to the heads.  If there is a break in the Seattle area rain this weekend, I'll puts some fresh plugs in and do a new check after some spirited driving as you suggested machoneman.
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area

427Fastback

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Re: compression test
« Reply #13 on: September 29, 2017, 10:32:00 AM »
A few notes.I was running oem pent roof covers with a pcv.During the repairs I put breathers in the valve covers and installed the rear Cobra style breather.I left all the breathers on as it appeared to like them.
I did have the tins under the rockers but when I took the engine apart awhile ago I was surprised to see I had forgotten to install the valley tray..

I was working at a High Performance Engine shop at the time of the build.(not the shop where my engine was f**cked with)
« Last Edit: September 29, 2017, 10:35:15 AM by 427Fastback »
1968 Mustang Fastback...427 MR 5spd (owned since 1977)
1967 Mustang coupe...Trans Am replica
1936 Diamond T 212BD
1990 Grizzly pick-up

jholmes217

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Re: compression test
« Reply #14 on: September 29, 2017, 11:03:33 AM »
I'm currently running PCV to carb spacer with air/oil separator, on passenger side valve cover, and factory breather with hose going into the air cleaner on the drivers side valve cover.  I am using the long fingered tins under the rockers.  My valve covers are the tall "Cobra 428" Blue Thunder valve covers with baffles.  I am using a Streetmaster intake manifold, and the valley pan wouldn't fit with it.  Exhaust crossover is block with thin sheet-metal from a tin can.

I assembled the engine myself in my garage, so I'm pretty sure nobody messed with it.
Jeff
1969 Mach 1 Q code 428 Cobra Jet
4 speed, 3:50 traction lock
Olympia WA. area