Compression Buildup

[crustydemons666]

Does anyone know why i might be getting some compression buildup in the sump of my 3tc?

 

Cheers

[Trev]

Blocked PCV system?

[altezzaclub]

yes- what sort of venting system do you have?

 

I'd expect a PCV valve taking air into the inlet manifold, which might be jammed shut as they need cleaning every now and then, and you should have a tube from the air cleaner into the tappet cover to let clean filtered air into the crankcase when the PCV sucks it out, and also to let dirty fumes back into the air cleaner when the PCV valve is shut.

 

The PCV should be shut at high manifold vacuums, so idle and light-throttle cruise, and open at low manifold vac times, like acceleration & going up hills

[rob83ke70]

it sucks air all the time and this is normal (at least on a 4k system) - the standard carburetor is built to compensate for this. Obviously it sucks less at idle than at high revs, and at wide open throttle with no vacuum it doesn't suck at all, but they do suck air all the time.

 

Robert.

[Andy43]

yes- what sort of venting system do you have?

 

I'd expect a PCV valve taking air into the inlet manifold, which might be jammed shut as they need cleaning every now and then, and you should have a tube from the air cleaner into the tappet cover to let clean filtered air into the crankcase when the PCV sucks it out, and also to let dirty fumes back into the air cleaner when the PCV valve is shut.

 

The PCV should be shut at high manifold vacuums, so idle and light-throttle cruise, and open at low manifold vac times, like acceleration & going up hills

 

Worn rings causing blow by

[altezzaclub]

Worn rings causing blow by

 

I expect so, but the PCV system is designed to clear it out.

 

The flow rate of a PCV valve is calibrated for a specific engine application. For the system to function normally, therefore, the PCV valve must adjust the flow rate as operating conditions change.

 

When the engine is off, the spring inside the valve pushes the pintle shut to seal the crankcase and prevent the escape of any residual vapors into the atmosphere.

 

When the engine starts, vacuum in the intake manifold pulls on the pintle and sucks the PCV valve open. The pintle is pulled up against the spring and moves to its highest position. But the tapered shape of the pintle does not allow maximum flow in this position. Instead, it restricts flow so the engine will idle smoothly.

 

The same thing happens during deceleration when intake vacuum is high. The pintle is pulled all the way up to reduce flow and minimize the effect of blowby on decel emissions.

 

When the engine is cruising under light load and at part throttle, there is less intake vacuum and less pull on the pintle. This allows the pintle to slide down to a mid-range position and allow more airflow.

 

Under high load or hard acceleration conditions, intake vacuum drops even more, allowing the spring inside the PCV valve to push the pintle valve even lower to its maximum flow position. If blowby pressure builds up faster than the PCV system can handle it, the excess pressure flows back through the breather hose to the air cleaner and is sucked back into the engine and burned.

 

The common replacement interval for many PCV valves is 50,000 miles, yet many engines have never had the PCV valve replaced.

 

A restricted or plugged PCV valve cannot pull moisture and blowby vapors out of the crankcase. This can cause engine-damaging sludge to form, and a backup of pressure that may force oil to leak past gaskets and seals.

 

http://www.aa1car.com/library/pcv.htm

[crustydemons666]

ive just replaced the rings and pistons in it. also i took the admission unit off and blocked the steel tube that runs under the exhuast. could that have anything to do with my problem.... ill go have a look at the PCV and see if its blocked

 

Cheers Zac