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How high were the RPM's when this appeared....
Are your pushrods straight?
ive only had the affected low compression cylinder push rods out and they look good, straight, rev limter is set at 7000rpm, wasnt pushing to hard on the day it happened
It sounds like a valve train issue to me...... but it is difficult to diagnose just hearing the video. I am not sure that a compression test tells you anything if the valves are not operating. Where is the cylinder getting the air from so it can compress the air? If the piston is at TDC when you insert the gage, there is no air to compress and zero psi would be reasonable. A better test may be to just pull the plug and crank it over. if the cylinder breathes through the spark plug hole, you may be alright.
A really simple check for major damage is to drain the oil. Look for metal pieces. Big pieces may block the hole and cause the oil to drain funny. A main, rod or wrist pin will likely put metal splinters in the oil that will glisten in the light. The splinters will not be big enough to pick out with your hands, but you will see the bronze or silver color and you can feel the grit if you rub the oil between your fingers. If you knocked a rod out you'll know it.
Last edited by 2mnyvets; Jul 20, 2018 at 07:11 AM.
Update - so i removed the shaft rocker from low compression cylinder, with the rocker on, it produces 120 psi, all others are 140+, with the rocker rermoved, ie valves fully closed when turning engine over, it only managed to produce about 70 psi and then after another few trys at turning over engine, ended up down at 10 psi, so what does that mean?? bent valve or ?? - there is alot of oily burnt crusts on the pistons, which is more than likely on the valves aswell, seen on my boroscope today
That is not the way to do a compression test.
The valves should be fully closed via normal operation, just like they are on the other 7 cylinders.
Also, when you do a compression check, make sure the throttle is not fully shut.
I am not sure that a compression test tells you anything if the valves are not operating. Where is the cylinder getting the air from so it can compress the air? If the piston is at TDC when you insert the gage, there is no air to compress and zero psi would be reasonable. A better test may be to just pull the plug and crank it over. if the cylinder breathes through the spark plug hole, you may be alright.
.
I should have been more clear. In his picture, the compression gauge is reading "10" in front of a cylinder with no rocker arms. Throttle plate position is important but it won't matter where his throttle plates are if the intake valve isn't opening.
Last edited by 2mnyvets; Jul 20, 2018 at 11:09 AM.
yeah very true about compression test, someone suggested it and yeah when you think about it, that wont work with both valves closed, stupid! lol
ive now got the intake off, all the velve train, rods look good, tomorrow i will remove head, the pistons have a thick oil crust over them, caused my engine eating alot oil in last month, blue arrows show where there was oil inbetween intake gasket, so pistons will need a clean job on them
and as suggested i will remove oil pan etc and check caps etc on rods
cheers guys
Last edited by corvettedave383; Jul 20, 2018 at 03:07 PM.
It sounds like a valve train issue to me...... but it is difficult to diagnose just hearing the video. I am not sure that a compression test tells you anything if the valves are not operating. Where is the cylinder getting the air from so it can compress the air? If the piston is at TDC when you insert the gage, there is no air to compress and zero psi would be reasonable. A better test may be to just pull the plug and crank it over. if the cylinder breathes through the spark plug hole, you may be alright.
A really simple check for major damage is to drain the oil. Look for metal pieces. Big pieces may block the hole and cause the oil to drain funny. A main, rod or wrist pin will likely put metal splinters in the oil that will glisten in the light. The splinters will not be big enough to pick out with your hands, but you will see the bronze or silver color and you can feel the grit if you rub the oil between your fingers. If you knocked a rod out you'll know it.
I think the noise is coming from deep inside engine, like either bent valve hitting piston or big end, is my guess
Ok, buncha 140 and 1 120? Close enough to even. Re-lap those 2 valves when head is off. This is a balanced rotating assy? Getting crank done or replacing it? Can you get 2 matching rods, or they stock chebby?
Ok, buncha 140 and 1 120? Close enough to even. Re-lap those 2 valves when head is off. This is a balanced rotating assy? Getting crank done or replacing it? Can you get 2 matching rods, or they stock chebby?
yes 1 cylinder at 120 and rest around 140+, yes balanced rotating assy, not sure about crank, need to look at it, it has a brc rotating assy, brc conecting rods
BRC how old? Brooks Racing Components went bankrupt in 04. Their cranks werent highly regarded. Tennesse engine something sold the name to a FL company. They are making pistons now and selling rotating assy packages where they are the middleman on the cranks and rods. This is not Bryant Racing...
BRC how old? Brooks Racing Components went bankrupt in 04. Their cranks werent highly regarded. Tennesse engine something sold the name to a FL company. They are making pistons now and selling rotating assy packages where they are the middleman on the cranks and rods. This is not Bryant Racing...
engine was built in 2008, sounds like ive got a right ******* then lol
Found my problem - Damaged gudgeon pin/top rod bearing, you can push piston down by 4 mm approx and move the piston clockwise/anti clockwise by 3 mm , fun times! and also scores on cylinder which your finger nail catches on
I listened to your video and thought about wrist pin, but it is a very uncommon failure with modern bushed rods and forged pistons with spiral lock floating pins
all the moving parts need assembly lube or oils for initial start up I've done some motors that put oil repellant coatings on the underside of the pistons. That keeps the piston assembly lighter and the wrist pin bathed in oil
Cheers guys interms of the scores, does that cylinder need a rebore i take it or can be honed out ? and if it needs rebore, are you meant to rebore all cylinders?
GLW rebuild. 
