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Author Topic: Trying to solve Multiple Problems  (Read 8951 times)
sschroeder
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« on: August 08, 2011, 07:04:49 pm »

I've got two problems with an engine I just installed in a custom vehicle. It's a 351w that's basically stock. I had a local reputable company that builds lots of engines build this for me. It's got a very mild RV cam in it. (Comp cams 260 grind) Here are the problems.

1. Low vacuum. I'm only getting about 11-12 inches at idle. The engine is basically stock, so with that cam I should be getting closer to 18 inches, I believe.

2. The engine overheats at idle, and at highway speeds. But it generally does OK in the mid-range speeds. Also, the headers arre getting too hot... like around 500-550 degrees.

Here's what I've done so far. I've sprayed carb cleaner all around the carb and intake to check for leaks. I didn't hear the RPMs change at all. I pulled the intake off and had it checked to make sure it wasn't warped and leaking internally somewhere. It's good. (it's an old Offenhauser 360 intake)

I did a compression check on it and found 2 cylinders at 110 lbs, 2 at 125 lbs and the rest around 150 lbs. 

I've messed with the timing quite a bit. I've retarded it and advanced it way up with no change to temps or vacuum. I've been running it normally at about 10 degrees advanced with a total of about 34-36 degrees.

I double checked the valve adjustment and they are all fine. 

The radiator has been pulled apart and checked twice. The water pump has been checked and is good. It is a stock Ford water pump, not a super high volume one.

The engine runs good, although maybe not as much power as I thought it would make. But otherwise pretty smooth, starts easily, etc.

Fuel mixture is a tad bit lean... maybe. I'm running an old AFB carb that came off another 351w running an almost identical setup (with the exception of the intake) and the mixture was fine.

We built another identical vehicle at the same time we built this one and it has none of these problems. Same body, same radiator, same motor and can hardly get it to heat up to 180. So that tells me the radiator is plenty big enough, etc. And since it heats up at 65mph as well as at idle, that tells me the fan isn't the problem. Even so, it appears to be pulling quite a bit of air at idle.

I should also mention that it does take a little while to heat up. Not like when you have a head gasket problem and are pumping compression into the water. The cooling system pressurizes, but doesn't get so much pressure that it blows water out. In fact, I"ve been able to put about 1500 miles on the motor, being careful to not let it idle to long and get too hot.

I'm assuming the low compression on some of the cylinders is causing the low vacuum, but any thoughts on whether it is also causing the overheating and the over temp headers?

Any thoughts anyone?
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Joel5.0
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« Reply #1 on: August 08, 2011, 09:41:51 pm »

Suggestions:

1. Re-check cam timing.... yup, cam events timing.
2. Have you checked for any exhaust related problems, excessive back-pressure, obstructions.
3. Vacuum with that cam is too low.
4. 110 ft-lbs in two cylinders is too close to the "power making" acceptable threshold.
5. Redo a cranking compression test with valves set a "zero lash".

LUK
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jayh
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« Reply #2 on: August 08, 2011, 10:28:07 pm »

the compression test results along with the low vacuum concern me. could be rocker preload or a valve job issue. can you do a leak down test?
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sschroeder
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« Reply #3 on: August 08, 2011, 11:07:57 pm »

I've checked all the valves and all are at zero lash when at TDC for that cylinder.  You can twirl the pushrods with your fingers with just a slight bit of resistance. 

I don't have a good way to do a leak down test, but I'm taking the vehicle to someone who can do that.  Unfortunately it'll be a week before that happens. 

I'm not certain what you mean by checking the cam timing.  I've doublechecked that #1 is at TDC when TBC on the balancer lines up with the pointer. 

I agree, the compression is very concerning.  I'm also concerned about the header temps.  It's making the underhood temps almost unbearable. 
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sschroeder
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« Reply #4 on: August 08, 2011, 11:09:17 pm »

Oh yeah, forgot to mention, the exhaust should be good.  It's brand new from the headers to the tailpipe.  I'm using short headers that came off a mustang. 
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Joel5.0
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« Reply #5 on: August 08, 2011, 11:22:52 pm »

Cam timing as in cam degreeing. Making sure the cam intake opening event @.050" tappet lift is 3° ATDC after you perform a true TDC setting with a piston stop.
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ACRONYMS:
LUK  LMK  JIC  BTSTDTRT  YCYDYP  NFI-YTM  SPOBI, and the classic... DILLIGAS

'86 Mustang GT, X-303 cam, Holley DP 700, RG Tran., 289 Heads   Ford Smilie 2


Quote from: Joel5.0
The right to be stupid is inalienable for sure however, there is no such thing as a right to impose stupidity onto others
Great Thoughts will Overwhelm a Feeble Mind
There is never money to do it right, but there's always money to do it over.
Knowledge based on external evidence is unreliable.
He, who doesn't ask, does not deserve an answer.
A mind is like a parachute it only works when it is open.  (oldmanjoe)
If you can't explain it simply, you don't understand it well enough. (Albert Einstein)
Tuning on a Dyno for the track, is like swim practice in a bathtub.
I can explain it for you, but I can't understand it for you. (90lxcoupe)
The proof of understanding is the ability to explain it. (H. Torruella)
Ignorance is bliss, but stupidity is orgasmic.
Fraud and falsehood only dread examination. Truth invites it. (Samuel Johnson)
The chaotic resistance of the opponents leads to the conclusion that they are not prepared to meet the challenge. The problem is already much more psychological then technological. [Bojidar Djordjev]
Individuals are rational and humane... Crowds are reactionary and barbaric. (Jason)
The person who says it cannot be done should not interrupt the person doing it. –Chinese Proverb
Nothing sways the stupid more than arguments they can't understand - Cardinal de Retz
sschroeder
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« Reply #6 on: August 09, 2011, 04:30:20 pm »

Yep.  Checked it last night.  Cam timing is correct, too. 
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69 Merc
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« Reply #7 on: August 09, 2011, 04:53:08 pm »

Next step I would think would be getting the tools for a leak-down test.
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Robert's 1969 Mercury Montego (FordStrokers 408W, QFT 850cfm RQ-AN, Super Victor, 1" aluminum open spacer, CamMotion HR .624"/.609" 251*/256* 108* LSA, 1-3/4"x3-1/2" headers, Dynomax Ultra #17224 mufflers, C6/4R100 trans, 8"/9" 5500 converter, Broader Performance manual V/B, 9" 4.56 Detroit Truetrac, Hoosier Pro Street 31x12.5R15 on 10" rims)

The Merc started here = http://sbftech.com/index.php/topic,27178.0.html  Now = http://sbftech.com/index.php/topic,34648.0.html

Thanks to Jim "Woody" and Nicole Woods @ FordStrokers 408W, Westminster Performance Transmission (W.P.T.) transmissions, TCS Performance converters, Broader Performance valvebodies and last but not least a BIG thanks (always) to my friends here and abroad in the World!
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« Reply #8 on: August 09, 2011, 06:27:33 pm »

I've checked all the valves and all are at zero lash when at TDC for that cylinder.   
At TDC the lifters are not on the base circle of the cam. I would go back over the valve adjustment using the procedure here. http://sbftech.com/index.php/topic,30962.0.html
 Good Luck!
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jayh
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« Reply #9 on: August 09, 2011, 07:34:25 pm »

you cant go by if the pushrods turn. are these pedestal rockers(bolt down) or are they adjustable?

a TDC between compression and power stroke(when the plug fires). you are indeed on the base of the cam
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sschroeder
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« Reply #10 on: August 11, 2011, 12:22:51 am »

They are bolt down, non-adjustable rockers.  We checked to pushrods at the top of the compression stroke when we assumed both valves would be closed.  We can recheck using the method mentioned in the earlier reply. 

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sschroeder
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« Reply #11 on: August 11, 2011, 12:25:58 am »

I should also say that I wasn't really trying to adjust the valves that way, I was just trying to make sure they weren't set too tight and therefore holding a valve open.  Or more correctly, I guess, too long a pushrod installed and therefore holding a valve open.  So my asumption is that if I can spin the pushrod with my fingers, there's not a valve open. 

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jayh
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« Reply #12 on: August 11, 2011, 09:05:45 am »

that is not always true. the lifter can bleed down a little allowing you to spin the pushrod
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sschroeder
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« Reply #13 on: August 11, 2011, 08:49:13 pm »

You're right.  I'd thought about that before I started doing all the checking, but then never thought about it again. 

It looks like I"m going to take the vehicle to the engine builder next week for him to do more testing.  He's got more tools and equipment for that, so hopefully I'll get an answer... and a fix. 

Thanks for the advice.
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« Reply #14 on: August 13, 2011, 11:10:48 pm »

Let us know how it goes for you, OK?      Good Luck!
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Robert's 1969 Mercury Montego (FordStrokers 408W, QFT 850cfm RQ-AN, Super Victor, 1" aluminum open spacer, CamMotion HR .624"/.609" 251*/256* 108* LSA, 1-3/4"x3-1/2" headers, Dynomax Ultra #17224 mufflers, C6/4R100 trans, 8"/9" 5500 converter, Broader Performance manual V/B, 9" 4.56 Detroit Truetrac, Hoosier Pro Street 31x12.5R15 on 10" rims)

The Merc started here = http://sbftech.com/index.php/topic,27178.0.html  Now = http://sbftech.com/index.php/topic,34648.0.html

Thanks to Jim "Woody" and Nicole Woods @ FordStrokers 408W, Westminster Performance Transmission (W.P.T.) transmissions, TCS Performance converters, Broader Performance valvebodies and last but not least a BIG thanks (always) to my friends here and abroad in the World!
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