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Discussion Starter #1
Looking at buying a 1972 Mustang fastback. I had the pre-purchase motor vehicle inspection compression test done on the 429 engine (unknown origin - Engine No. 1J227610) in it. The average psi over all the cylinders was 125psi. Is that low? I’ve been told it is and that the heads might be worn or the head/inlet gaskets might be compromised. There was also a lot of brown sludge in the radiator reservoir. It wasn’t oily but I can’t explain its origins?

Any help you can give me on my enquirers would be truly appreciated👍
Cheers
Carl
 

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does it smoke?

I'm not an engine builder, but I would say that is low.
Compression test readings vary depending on the camshaft. (big cam, lower compression reading. small cam, higher compression reading)
unless that thing has a big lumpy cam, something is wearing out.

a usual culprit is the piston rings, so i wouldn't count on being able to get by with just reworking the heads/gaskets.

there are further tests you can do to help nail it down. a leakdown test could help you determine if its valves or rings.
or you could do the quick ring test - squirt a teaspoon or two of oil in there and run the test again. if your numbers jump, the rings are worn.
 

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Discussion Starter #3
Thanks Mate for your detailed reply, which is truly appreciated. It doesn’t smoke but I will get those other tests done to narrow down the issue/s hopefully. I’ll keep you updated:)
Cheers
Carl
 

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Thank you all for your support and replies to my questions which I truly appreciate:)

No it doesn’t smoke and burn oil.

Taking on board the consensus of what has been said I’ve done the following Compression tests:-
Hot Engine - Compression Test Results (PSI)

Cylinder 1

Dry - 135

Wet - 150

Cylinder 2

Dry - 150

Wet - 155

Cylinder 3

Dry - 150

Wet - 150

Cylinder 4

Dry - 150

Wet - 150

Cylinder 5

Dry - 150

Wet - 150

Cylinder 6

Dry - 150

Wet - 165

Cylinder 7

Dry - 150

Wet - 165

Cylinder 8

Dry - 150

Wet - 150

Cold Engine Compression Test Results (PSI)

Cylinder 1
Dry - 125

Cylinder 2
Dry - 120

Cylinder 3
Dry - 120

Cylinder 4
Dry - 135

Cylinder 5
Dry - 135

Cylinder 6
Dry - 117

Cylinder 7
Dry - 135

Cylinder 8
Dry - 135

Are these hot engine compression test results good for a 1971 - 429 Engine or are there some signs of the head gasket being compromised and/or valve problems - worn heads. In other words should I dump and burn and forget about buying this Mustang and try to find one with a healthier and stronger Engine or is this one good enough within the acceptable compression ratio limits for this big block Engine.



Any further feedback upon reviewing these results would be great!

Cheers

Carl👍
 

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Discussion Starter #6
72 Stang with a 429. Ford didn't put that in there. Check much deeper on this one.
Thank you all for your support and replies to my questions which I truly appreciate:)

Taking on board the consensus of what has been said I’ve done the following Compression tests:-
Hot Engine - Compression Test Results (PSI)

Cylinder 1

Dry - 135

Wet - 150

Cylinder 2

Dry - 150

Wet - 155

Cylinder 3

Dry - 150

Wet - 150

Cylinder 4

Dry - 150

Wet - 150

Cylinder 5

Dry - 150

Wet - 150

Cylinder 6

Dry - 150

Wet - 165

Cylinder 7

Dry - 150

Wet - 165

Cylinder 8

Dry - 150

Wet - 150

Cold Engine Compression Test Results (PSI)

Cylinder 1
Dry - 125

Cylinder 2
Dry - 120

Cylinder 3
Dry - 120

Cylinder 4
Dry - 135

Cylinder 5
Dry - 135

Cylinder 6
Dry - 117

Cylinder 7
Dry - 135

Cylinder 8
Dry - 135

Are these hot engine compression test results good for a 1971 - 429 Engine or are there some signs of the head gasket being compromised and/or valve problems - worn heads. In other words should I dump and burn and forget about buying this Mustang and try to find one with a healthier and stronger Engine or is this one good enough within the acceptable compression ratio limits for this big block Engine.



Any further feedback upon reviewing these results would be great!

Cheers

Carl👍
 

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those numbers don't look too bad (again, i'm not an engine expert).
you've got a few cylinders that show a 15psi jump between wet/dry, which indicates ring wear.
but overall, i'd say not bad.
 

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71 will show higher comp PSI due to higher comp ratio then a 72 will. They're about right. No bad holes so that's a big relief. Are you sure it's a 72 Stang with a 429? Not a 351C? What's the first 5 digits of the VIN?
Not that a 429 wouldn't fit nicely. Same engine bay as the 71s that Ford did put the 429CJ/SCJ in.
 

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Discussion Starter #9
71 will show higher comp PSI due to higher comp ratio then a 72 will. They're about right. No bad holes so that's a big relief. Are you sure it's a 72 Stang with a 429? Not a 351C? What's the first 5 digits of the VIN?
Not that a 429 wouldn't fit nicely. Same engine bay as the 71s that Ford did put the 429CJ/SCJ in.
Thanks for your reply. The 72 Mustang originally had a 302 under the bonnet at some point in time the 429 engine was thrown in. The engine no. Is 1J22
71 will show higher comp PSI due to higher comp ratio then a 72 will. They're about right. No bad holes so that's a big relief. Are you sure it's a 72 Stang with a 429? Not a 351C? What's the first 5 digits of the VIN?
Not that a 429 wouldn't fit nicely. Same engine bay as the 71s that Ford did put the 429CJ/SCJ in.
those numbers don't look too bad (again, i'm not an engine expert).
you've got a few cylinders that show a 15psi jump between wet/dry, which indicates ring wear.
but overall, i'd say not bad.
Yeah I noticed that as well. Lucky it’s no too big a jump, but the rings are starting to wear which I’m going to take up with the seller.
Thanks for your input😉
Cheers
Carl
 

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Discussion Starter #10
72 Stang with a 429. Ford didn't put that in there. Check much deeper on this one.
Thanks for your reply. The 72 Mustang Fastback originally had a 302 under the bonnet. At some point in time a 429 - engine no. 1J227610, was thrown in it with a C6. That’s a relief that the compression results aren’t bad. Appreciate all
The detail in your responses🙂
Cheers
Carl
 

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If the car runs good and you like it and feel happy about the price, I wouldn't worry about the rings. You can always doa mild rebuild later and make it all the way you want it. Even the guys on the 460Ford website will tell you the samething. Bing is always nice on a BBF.
 

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Discussion Starter #13
Ok got it👌Also noticed weld marks on the sump and made enquirers about this. Just been told that the sump may have had to be modified to fit into the 72 Mustang fastback because the 429 engine might have come out of a truck. The deck is also taller so the bonnet has to be modified as well.
Is there any significant differences between 429 truck and 429 sedan engines in terms of quality, longevity and performance?
Thanks
Cheers
Carl
 

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pretty sad - an fittings with hose clamps
So let's see your build. Heater hoses are a little different then oil and fuel lines. Some of us aren't afraid to show you ours no matter how childish the feedback.
And for you "experts", this type of hose end, a clamp is "recommended" but not always required. Depends on the application.
 

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Ok got it👌Also noticed weld marks on the sump and made enquirers about this. Just been told that the sump may have had to be modified to fit into the 72 Mustang fastback because the 429 engine might have come out of a truck. The deck is also taller so the bonnet has to be modified as well.
Is there any significant differences between 429 truck and 429 sedan engines in terms of quality, longevity and performance?
Thanks
Cheers
Carl
Con rods are the only real difference until you get into the carb and dist. Trans should be stronger. Unlike the 352s and 390s. Those had a much different crank snout.
 

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The compression numbers on an engine can vary wildly based on which cam is in it, head and piston combo, and even the gauge. If you have 10% variance or less across all 8, you are generally good.
 
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