[DeTomaso] 302 diagnosis

Sun Feb 24 21:10:08 EST 2008

The 408 stroker in my first car.

I have an idea but am uncertain of the cause for lifter/lobe wear.  We 
detected a problem a few years back at the club dyno day.  Above 5000 RPM 
the HP and Torque curve went haywire.  I had sent the dyno report to JC and 
without any doubt, he diagnosed it as a valve train issue.  I assumed it was 
a broken or weak set of valve springs.  Since the stroker seemed pretty fast 
(it still had the most torque at the dyno day, but not HP which the local 
guys won't let me forget) and ran well, I was pretty lazy about addressing 
the issue.  I was just disciplined to keep the engine below 5000RPM.  Also, 
I had been out of town for almost a year.

On several occasions I removed the valve covers and inspected the springs 
with a flashlight and mirror to see around the backside, but could find 
nothing obvious.  Recently Will Kooiman lent me a valve spring pressure 
checker that worked with the valve train fully assembled.  I knew the 
springs pressure rating at 1.75" and began to check each spring at that 
height.  With the car in 5th, we would roll it and watch the spring collapse 
to that height.  Working from #8 forward, when we got to #3I there was no 
lift.  While we stopped the exercise at that point, upon engine disassembly, 
the #2 intake lobe and lifter (that we hadn't checked) had even more wear. 
#6 was worn, yet enough to open the valve.  I am amazed at how well the car 
ran on 6 cylinders - including 2 BBORR events when I blew by Mad Dawg on a 
warm-up run.  :^)

Certainly a contributor was the implementation of heavier valve springs.  I 
had originally told the cam builder that I hadn't planned on running the 
engine over 6000RPM.  However, when we originally dynoed the engine on a 
stand, the HP curve was still rising when the valves floated at 6300RPM. 
The engine guy said that I had over 500HP in there if the springs were 
stronger.  With that tidbit of knowledge, when I replaced the cracked cast 
crank for a forged unit a year later, I took the opportunity to put stronger 
springs on the heads.

Well, as they say - the rest is history.

Yesterday, I installed a Crane hydraulic roller and while Desktop Dyno 
doesn't give me 500HP below 6000RPM.. It does give me over 500lbs of torque 
from 2000 to 4500 RPM.  That kinda sounds like fun.  I degreed the cam last 
night and attached the oil pan and heads today.  Ought to know better in 
about a month when I've got it back on the road.  I am repainting the rear 
trunk area and that will take a little time.

JT
----- Original Message ----- 
From: "Charles Engles" <cengles at cox.net>
To: "John Taphorn" <jtaphorn at kingwoodcable.com>
Cc: <detomaso at realbig.com>
Sent: Sunday, February 24, 2008 3:37 PM
Subject: Re: [DeTomaso] 302 diagnosis

> Dear John,
>
>               Which engine is this that you're rebuilding?    The stroker 
> in your first Pantera or the non-stroker (?) in your second Pantera?
>                Next dumb question: why would the lobe and lifters wear 
> down as partners on intakes #2,3,& 6?
>
>                             Warmest regards,  Chuck Engles
>
>
>
> ----- Original Message ----- 
> From: "John Taphorn" <jtaphorn at kingwoodcable.com>
> To: "dyogi" <dyogi at hawaii.rr.com>
> Cc: <detomaso at realbig.com>
> Sent: Sunday, February 24, 2008 2:42 PM
> Subject: Re: [DeTomaso] 302 diagnosis
>
>
>> Dennis
>>
>> I am presently rebuilding my engine.  Lobe and lifters wore down as 
>> partners on intake 2,3&6.  I had low vacuum and didn't check compression, 
>> but since the intakes were not opening, it had to be down.
>>
>> Although, I suppose you checked the cam last time apart, the problem may 
>> have occurred on start up.
>>
>> We diagnosed mine by noticing the rocker arm wasn't moving to open the 
>> valve.
>>
>> JT
>>
>> ----- Original Message ----- 
>> From: "dyogi" <dyogi at hawaii.rr.com>
>> To: "'P. Rimov'" <rimov at charter.net>
>> Cc: <detomaso at realbig.com>
>> Sent: Sunday, February 24, 2008 12:54 PM
>> Subject: Re: [DeTomaso] 302 diagnosis
>>
>>
>>> Paul,
>>>
>>> Thanks for the reply.  The internal vacuum leak was brought up before. 
>>> The
>>> plugs don't get oily and appear normal.  I actually have already pulled 
>>> and
>>> resealed the intake using Felpro gaskets with no improvement.
>>>
>>> No coolant in the oil and no oil in the coolant so I don't think that 
>>> it's
>>> the head gaskets.  The motor has 24,000 on it and the bores looked good 
>>> when
>>> it was apart.
>>>
>>> Aloha,
>>>
>>> Dennis
>>>
>>> -----Original Message-----
>>> From: P. Rimov [mailto:rimov at charter.net]
>>> Sent: Sunday, February 24, 2008 7:09 AM
>>> To: Dennis Yogi; Dennis Yogi
>>> Subject: Re: [DeTomaso] 302 diagnosis
>>>
>>> Mr. Yogi:
>>>
>>> You should be pulling 14-18hg with a mild cam like that. Have you pulled 
>>> the
>>> spark plugs just after the engine dies? If any of them are dark and oily
>>> you may very well have an internal vacuum leak were the gasket is sealed 
>>> on
>>> the outside of the intake manifold and heads but is not sealed well 
>>> between
>>> the intake manifold and lower ports. When the engine warms and the 
>>> engine
>>> parts expand
>>> at different rates the leak becomes more prevalent and the problem 
>>> become
>>> more apparent
>>> more common with the turkey pan style gasket than good quality FMS and
>>> Felpro gaskets.
>>>
>>> Also the compression is really low,,,
>>> Make sure your gauge is working accurately. Compression should be 
>>> 120-130.
>>> Could be valve(s) or piston rings failing. Have you checked your oil for 
>>> any
>>>
>>> coolant. A blown or leaking head
>>> gaskets could be causing the low compression.
>>>
>>> Although a pain, the first thing I would do would replace the intake 
>>> gaskets
>>>
>>> and double check the
>>> gauge and your engine compression also check your oil for contaminates
>>>
>>>
>>> Paul
>>>
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>>
>>
>>
>
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