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Volvo Penta AQ200d V8

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peterwright

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Hi. I have just joined this forum. I have a Fairline Holiday with an AQ200D V8 installed. Having mega problems with misfiring on cylinders 1,3,5 and 7 (right hand bank looking from waterpump end) I have replaced just about everything on the electrical side, plugs, leads (Moroso), dist.cap, rotor, points, coil, ballast, capacitor, advance springs, all to no avail. I have set the timing with a dwell meter and zenon strobe to exactly the manufacturers spec.
All fuel filters have been changed, carb stripped and rebuilt with kit.
Mallory of the US advised that I should check the cylinder pressures. They are all in range of 105 to 110psi. Is this correct??
If they are out of spec, what would cause all 8 cylinders to be below pressure?
Does anybody know what the correct cylinder pressures should be
Peter
 
Peter, this will get you some info on the AQ 200D.

The problem with an engine that we have little history on, is who did what to this engine previously?
All four of your cylinder readings are low, IMO.
They are all on the same bank.
If the engine was set up for 64cc chamber cylinder heads, yet at one point a 76cc chamber cylinder head had been installed on this one bank....., it may explain the difference if these four cylinder pressures.

So.... I think you have some homework to complete. Post back with your findings!
 
Hi Ricado
Many thanks for the info. I do not have any history for the engine. I purchased the boat 4 months ago. I do have a considerable number of repair and maintainence bills, bit nothing relating to an engine strip down.
Just a note, all 8 cylinders are performing at around 105 to 110psi. What I will do is check my compression meter to make absolutely sure it is reading right.
The engine has hardly been used for the past three years and has only ever done river cruising at 1500 revs max. Is it possible that the inlet valves are coked up, not closing properly hense low cylinder pressure?
Peter
 
Peter,

Did you try a compression test after adding oil to cylinders?
Your gauge may also be reading low, so if all cylinders are even, you may be ok in that matter.

Other things to look for.

Condenser changed? Try wiggling the wire at condenser. Is it intact?

You said coil was replaced; inside of coil where coil wire attaches there is a screw that holds female terminal in place, is it secure?

How is distributor shaft bushing condition? Any play in shaft?

Wire terminals for ignition system; Loose? Corroded?

Check ignition switch connections.....and Switch?

Does it idle ok?

Maybe the valve lash is not correct??? This would involve removing the valve covers and checking with the engine in proper position.

John
 
Hi Duo-prop
many thanks for your suggestions. I will try and do the compression tests again after putting oil down each chamber to see if I get a different reading. I will also check the compression tester to see if reading correct. I have also checked all the other items mentioned. The distributor shaft has about two to three thou play which I should think is within tolerance. One strange thing is the carbon rod in the DC is off centre to the rotor. I have replaced the DC with a new one and still the rod is off centre to the rotor. Any ideas?
Thanks Peter Distributor rotor 002.jpg
 
Peter, the distributor cap carbon button should be centered over the distributor shaft.
From the looks of your rotor, it is off a tad (see green circle), but remains centered rotationally.

If this is an older Mallory, it may require the smaller diameter cap..... perhaps the "flat" cap!
If the larger cap is installed (and I've never done this) it may be resting off center.... which may increase the gap between the rotor tip and cap contacts on one side.
Check the OD dimension (between the red arrows) against your cap ID dimension.

Old point style Mallory modified.jpg

Points:
Are you setting point "dwell", or relying on "gap"?
Gap is an estimate ONLY of correct dwell.
You'll need to set your contacts points using a dwell meter for best results.

Timing:
Set BASE advance, but you must also see where the Ignition TA or TAT is (total advance timing).
Without the correct TA, the engine will not perform as expected or hoped for.
See your OEM specs for this.
If you need help with the TA procedure, post back.





peterwright said:
Hi Ricado
  • Just a note, all 8 cylinders are performing at around 105 to 110psi.
  • What I will do is check my compression meter to make absolutely sure it is reading right.
  • Is it possible that the inlet valves are coked up, not closing properly hense low cylinder pressure?
Peter
Click to expand...
Your Comp readings are close enough together for this alone to be a good sign. Let's hope that your gauge is off a tad. Are you using the correct compression testing procedure?

Yes, it is possible, however, your readings are very close to one another!



As for a "wet" test, there is a caveat to this for a V-8 engine.

First, you may have the full dished pistons..... of which means that a tremendous amount of oil will be required to reach the ring landings in a radial fashion.
The more oil added, the more volume the oil consumes, and the greater the cylinder pressure is increased.
But to what amount does this alone increase cylinder pressure as aposed to actually temporarly sealing the rings?????

Secondly, this is a V engine..... gravity plays against us when we attempt to wet the ring landings.... meaning that it pulls any oil to the low side of the ring landings, preventing an equal and radial wetting of the rings.
I could add 18cc of oil to a cylinder and show you a pressure increase from the oil volume alone.

Point being........ it's not always a reliable method to determine if piston rings are bad/good for a V engine.

I'd rather see you do a cold/warm compression test, and compare readings.
Perhaps follow that with a cylinder leak-down test.

.
 
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