Low compression 400 UPDATE
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Tuned
Joined: Mar 2017
Posts: 351
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Low compression 400 UPDATE
Trucks been running bad. Produces a ton of blow by. Seems like a couple weeks ago it started that all of a sudden. Did a compression test and 1&2 have 30 psi. Everything else is 150-120. Poured 1 gallon oil jug cap into 1&2. Bumped them to 40-45 psi. Poured another 2 caps in each one and got the same result.
Do you guys think a leak down test is necessary in order to diagnose and fix what’s wrong? I’d have to buy a gauge.
Other than that what else can I do to diagnose what’s wrong before I remove the head? Someone told me a head gasket could make the 2 cylinders beside each other go down like that.
Do you guys think a leak down test is necessary in order to diagnose and fix what’s wrong? I’d have to buy a gauge.
Other than that what else can I do to diagnose what’s wrong before I remove the head? Someone told me a head gasket could make the 2 cylinders beside each other go down like that.
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Tuned
Joined: Mar 2017
Posts: 351
Likes: 57
Well it was the head gasket. About an inch missing between the 1&2 cylinders right at the thinnest point.
Seems like like been leaking into almost all 4 cylinders on this head. Most of the valves have an 1/8 inch of crust on them.
I want to rebuild these locally. I don’t really want to reuse my old lifters and I’m not sure if it’s even a good idea to put new springs on old lifters? Looking at a comp cams 252h grind. Seems suitable for my engine and the kit is ~$550.
Does that sound like a horrible idea to anyone?
I’ve already got a straight up timing gear installed so I’d do that again. I’d remove my engine and put it on a stand to do this. I’d like to repaint it but that seems risky since I’m not wanting to remove the bottom end at all. I’d hate to blow some nastiness somewhere if shouldn’t be just for a repaint.
Im not an engine rebuilder so I’m just looking for suggestions. I don’t want to go through the bottom end on this engine right now. It had good compression before the gasket leak.
Id like a 87 octane smooth idle low rpm torque gas sipper hopefully.
Seems like like been leaking into almost all 4 cylinders on this head. Most of the valves have an 1/8 inch of crust on them.
I want to rebuild these locally. I don’t really want to reuse my old lifters and I’m not sure if it’s even a good idea to put new springs on old lifters? Looking at a comp cams 252h grind. Seems suitable for my engine and the kit is ~$550.
Does that sound like a horrible idea to anyone?
I’ve already got a straight up timing gear installed so I’d do that again. I’d remove my engine and put it on a stand to do this. I’d like to repaint it but that seems risky since I’m not wanting to remove the bottom end at all. I’d hate to blow some nastiness somewhere if shouldn’t be just for a repaint.
Im not an engine rebuilder so I’m just looking for suggestions. I don’t want to go through the bottom end on this engine right now. It had good compression before the gasket leak.
Id like a 87 octane smooth idle low rpm torque gas sipper hopefully.
Hotshot
Joined: Jul 2020
Posts: 10,550
Likes: 2,669
From: Near Salt Lake City
Sweet, you'll have it fixed in a jiffy
Why tear into the cam and lifters?
Have you inspected the pushrod travel and or inspected the lifters? and verified the cam and lifters are shot?
I agree, with a blown head gasket the rest of the engine might need attention.
Doing that will however warrant main and rod bearing check and subsequent replacement
Look for all NOS Ford parts. Cam lifters and bearings
Use anybody's gaskets but keep an expensive valley pan intake gasket on there
Why tear into the cam and lifters?
Have you inspected the pushrod travel and or inspected the lifters? and verified the cam and lifters are shot?
I agree, with a blown head gasket the rest of the engine might need attention.
Doing that will however warrant main and rod bearing check and subsequent replacement
Look for all NOS Ford parts. Cam lifters and bearings
Use anybody's gaskets but keep an expensive valley pan intake gasket on there
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Tuned
Joined: Mar 2017
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I don’t think there’s really anything wrong with the cam or lifters it just seems silly to me to reuse the old ones. I’m not really looking for a power gain but I believe this is the first build on this engine so it just seemed like a good idea to me to replace the springs, guides, lifters, and cam in one go.
Why would that mean I have to replace the main bearings?
Why would that mean I have to replace the main bearings?
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Hotshot
Joined: Feb 2004
Posts: 10,847
Likes: 2,615
From: The Shenandoah Valley
I don’t think there’s really anything wrong with the cam or lifters it just seems silly to me to reuse the old ones. I’m not really looking for a power gain but I believe this is the first build on this engine so it just seemed like a good idea to me to replace the springs, guides, lifters, and cam in one go.
Why would that mean I have to replace the main bearings?
Why would that mean I have to replace the main bearings?
If you are going to pull the engine out to do the heads, there is no reason to not do bearings. You'll see.
Hotshot
Joined: Jul 2020
Posts: 10,550
Likes: 2,669
From: Near Salt Lake City
You are right there and I would check the valves and guides too
Pull a few lifters out and see how dished (or not) they are
Tear down and reassembly is cheap and easy
The cam will need to be broken in correctly using the assembly lube in the kit
It's fun rebuilding a 400 but not cheap compared to some others
It probably needs it if it ran long enough for the metal mites to eat that head gasket
Pull a few lifters out and see how dished (or not) they are
Tear down and reassembly is cheap and easy
The cam will need to be broken in correctly using the assembly lube in the kit
It's fun rebuilding a 400 but not cheap compared to some others
It probably needs it if it ran long enough for the metal mites to eat that head gasket
Hotshot
Joined: Jul 2020
Posts: 10,550
Likes: 2,669
From: Near Salt Lake City
You would not necessarily need to replace the main and rod bearings
It is just that while you are doing engine work and having it on a stand none the less
Means you should check the bearings and replace the pan gasket
Upon doing that you are likely to find the main and rod bearings are worn down to the Babbitt (the soft bronze looking stuff)
It is just that while you are doing engine work and having it on a stand none the less
Means you should check the bearings and replace the pan gasket
Upon doing that you are likely to find the main and rod bearings are worn down to the Babbitt (the soft bronze looking stuff)
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Tuned
Joined: Mar 2017
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I haven’t pulled the lifters out. I made sure to keep the order of the rockers and pushrods.
2-3 years ago I put a straight up timing chain in while I had the radiator out and was doing a water pump. Me and a buddy pulled a couple of the main caps off and they seemed to be in perfect condition. The truck got a new oil pump at that time also.
2-3 years ago I put a straight up timing chain in while I had the radiator out and was doing a water pump. Me and a buddy pulled a couple of the main caps off and they seemed to be in perfect condition. The truck got a new oil pump at that time also.
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Tuned
Joined: Mar 2017
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I really was just going to get a new cam kit because it didn’t make sense to me to reuse the old springs on my rebuilt heads or new springs on my old lifters. And it didn’t make much sense to reuse my old lifters as they are such a critical wear component. I know that all has to be down at the same time. I could just reuse the lifters and not do the cam kit. I am removing the engine for reassembly.
Hotshot
Joined: Jul 2020
Posts: 10,550
Likes: 2,669
From: Near Salt Lake City
Sounds good and right on the bearings, no need to recheck them
Just be careful with the new cam and lifters break in and do exactly what they say and use their special grease
It may go south anyway it seems with new cam and lifters these days
Do everything right and try to stay away from parts made in China is my advice
That may not be possible these days
Just be careful with the new cam and lifters break in and do exactly what they say and use their special grease
It may go south anyway it seems with new cam and lifters these days
Do everything right and try to stay away from parts made in China is my advice
That may not be possible these days
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