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GMC c7500: truck 05 gmc c7500 8.1 engine 55000 miles engine…

Customer Question
truck 05 gmc c7500 8.1...

truck 05 gmc c7500 8.1 engine 55000 miles engine droped valve busting piston head of valve found in oil pan part of valve steam found in intake installed long block truck idoles fine but on test drive at high rpm seems to have valves hit piston bent 2 push rods installed 2 longblock runs fine up to 2500 rpm afert that makes nosy have to shut off when trying to restart cranks like no compression on several cyls when it starts miss for while then smothes back out

Submitted: 9 years ago.Category: Medium and Heavy Trucks
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Answered in 32 minutes by:
10/2/2012
Technician: Jeremy, Certified Truck/Bus Technician replied 9 years ago
Jeremy
Jeremy, Certified Truck/Bus Technician
Category: Medium and Heavy Trucks
Satisfied Customers: 4,370
Experience: ASE Med/HD Truck Technician, NATEF Diesel Engines and Electrical/Electronics Technician, Network Engineer specializing in CAN faults, Aftertertreatment, and vehicle communications
Verified

My name is Jeremy and I will try to assist you.

 

Were the heads rebuilt after the valve drop?

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Customer reply replied 9 years ago

a long block with rebuilt heads installed 2 times

Technician: Jeremy, Certified Truck/Bus Technician replied 9 years ago

Presuming all the parts are good and they were installed as they should, the only other thing that can cause that problem is the timing being off. Was all the timing checked out?

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Customer reply replied 9 years ago

it has coil pac for each cyl there is no timing to set

Technician: Jeremy, Certified Truck/Bus Technician replied 9 years ago
It has timing to set between the crankshaft and the camshaft. If the pistons are hitting the valves, the timing is off, the piston or rod is wrong, the valve spring is bad, there could be many mechanical issues there. They should not touch or even come close...Check the timing marks at the front of the engine to verify it is good.
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Customer reply replied 9 years ago

yes we have checked cam and crank timing are set dot to dot

,

yes we have checked cam and crank timing are set dot to dot</p crankat 12 cam at 6

Technician: Jeremy, Certified Truck/Bus Technician replied 9 years ago
I'm not sure what else can cause the piston hitting other than what I mentioned.

I'll opt out and see if another expert can assist.
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Technician: Wayne, Journeyman replied 9 years ago
Wayne
Wayne, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 17,761
Experience: worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling
Verified
Hi I'm Wayne
I will try to help you also
Good Afternoon,

I will throw my 2c in here
are you running solids or hydraulic lifters
Did you clay the heads , to check clearance of valves 3
are you running with guide plates for push rod tubes
Let me know
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Customer reply replied 9 years ago

this is a stock 8.1 with hyd lifters

Technician: Wayne, Journeyman replied 9 years ago
Hi Thank you for that
Well 2 long blocks , back to back ,
doing the same thing, Is it always the same cylinder
are these reman blocks, from where
Hope you do not say Jasper engines
how long do they run before this happens
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Customer reply replied 9 years ago


this second long block has not bent push rods yet when i herd the nosy i cut it off started it back it had several cyl missing but after it idoled for awhile it smoothed out i was able to drive back to my shop 1 mile as long as i keep rpm below 2500 no problem

Technician: Wayne, Journeyman replied 9 years ago
Hi Thank you for That

You did not mention, How long did this run,Where you bought them from,
and always the same cylinder
Last I forgot to ask what is your oil pressure , at idle and at 2500 RPM
These are important things for me to know,
as a engine rebuilder for 34+ years
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Customer reply replied 9 years ago

oil pressure at idol 35 2500 50 the co that owns the truck had them shipped in

Technician: Wayne, Journeyman replied 9 years ago
Hi OK,
with all this info we collected
here is my suggestions,
#1 remove and clay the heads for clearance
#2 I believe the wrong head gasket,
they are using for a Vortec head
#3 change over to solid lifters, remove the guide plates
Reason being Hydraulics will float at a high RPM
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Customer reply replied 9 years ago

this is a c7500 work truck with 8.1 stock engine the co would not want to chang i am try to fig if the engine builder is doing wrong or somthing i am over looking i have done truck repair for 45 years and never had such a problem

Technician: Wayne, Journeyman replied 9 years ago
Hi
Thank you for that
I seen in this thread , everything that has been covered,
tried, checked,
lets put it into perspective,
Some thing is Wrong, head gaskets, wrong, head milled out of Specs
oil pressure too high, keeping lifters from going soft
I still take the stand , the heads need to be Clayed to check. clearance
I do not know what else to say to you , your not following suggestions,
just saying the rebuilder, does these engines,
How do you know they are doing these correct,
Need to check Specs. That is what is all about , rebuilding engines
What about Warranty , must be on ever one
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Customer reply replied 9 years ago
What you don't understand the rebuilder does not want me to tear it apart I need to make sure I covered and checked the installation to make sure my mech did nothing wrong
Technician: Wayne, Journeyman replied 9 years ago
Hi
Your Mechanic did nothing wrong
I will back him 100% ,
He checked timing, he checked, gear train timing,
he installed a drop in engine
they are at fault.................
you are correct, rebuilder never wants you to take apart, same as my self, if so
Warranty VOID
They have a Problem , and you need to take your stand , for engine Spec
you want head clearance, (clay )
You are the Customer , you Pay
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Technician: Wayne, Journeyman replied 9 years ago
HI

I'm just following up with you to see how everything is going. Did my answer help?


Let me know,
Wayne
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Wayne
Wayne
Wayne, Journeyman
Category: Medium and Heavy Trucks
Satisfied Customers: 17,761
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Experience: worked on, Gmc, Macks, Freight liner,Mercedes Benz,,Ford, sterling

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