Mind-bending timing problem on Volvo Penta AQ211A engine

ShaunL

Recruit
Joined
May 21, 2019
Messages
1
Hi All,

Although I've read through many forums over the years (including this one), I am newly registered here.
I have a timing problem that is really "doing my crust" that I just can't fathom, so any help is greatly appreciated.

I have fitted a recon Volvo Penta AQ211A to my boat, but have never been able to get the timing "right".

My apologies if this is long-winded, but I know that in order for anyone to help I'll need to tell the whole story.

The original AQ211A engine destroyed itself after being winterised for over 2 years (I have some interesting photo's, but that's another story).

So, I bought a reconditioned engine, complete with cylinder heads from an Ebay marine engine reconditioning company. I believe the block was new (at least, that's what they told me). The heads were re-conditioned ones.

A lot of parts from the original engine were swapped over, including the carb (now replaced), distributor, cam-chain timing cover, pulleys, Exhaust and inlet manifolds.

However, (and it *might* be relevant), I had to use the harmonic balancer from a slightly newer engine, and I believe it's from an automobile. But, the key-way and TDC marks were in the same places as the original.

My problem is the ignition timing. But it's NOT as simple (or maybe it is) as it first appears.

So, I rotated the engine and found TDC. No1 piston at the top, valves closed, rotor arm pointing at No1 lead.
Checked firing order (several times), as far as I can see everything "static" is correct.

So, now is where it gets weird...... The engine refused to start, so I rotated the distributor until it fired-up, checked the timing (should be 6 Deg BTDC @ 750 RPM) but found that it was initially at around 16 - 18 Deg BTDC.

If I reset the timing (using an advancing timing light - a brand new one) to 6 Deg, the engine runs rough. At this point, if I open the throttle it mis-fires through the carb and stalls.

So, I set the timing "by ear". When I do this, ignoring timing marks, I can get the engine running sweetly, instant response on the throttle, easy starting, no misfiring, steady idle, all as you would expect.

And this is where it gets really really weird! ....I put the timing light back on and dialled-in until I could see what the timing actually is. It appears to be: 20 Deg BTDC @ 750 RPM (should be 6 Deg) and 34 Deg BTDC @ 2500 RPM (should 14 Deg BTDC) according to the cam-chain cover marks. (using the deepest V as the TDC mark).

I confirmed this (as best I can) with a standard non-advancing timing light, several times.
I suspected something somewhere is way "out-of-whack", so I stripped the entire HT ignition setup down, started from scratch, one lead at a time, re-confirmed firing order, rotation of rotar-arm (clockwise). Still the same!

So, I stripped the distributor. The distributor is a Prestolite (I think) but the points have been changed for an electronic (hall effect) pickup. Centrifugal weights move freely (cleaned and lightly re-greased pivot-points anyway), springs are intact and firm, everything appears to operate as expected. (No vacuum advance on these things).

But, still the timing appears to be "way off their marks".

Someone suggested "Well, if you've done it by ear and it runs, close it up and forget it!", but that doesn't work for me.
I want to know that the timing is as accurate as I can get it. Besides, I just can't get my head around why the timing can appear to be so far off the marks, and run infinitely better than if it's "timed correctly".

Could it be something to do with the hall effect "points"? Is it possible the cam-chain cover from the original engine has the timing marks in the wrong place for this engine? (They are on the right-hand side, down between the cooling hoses).
Did the V8 ever have timing marks in a different position (more round to the left-hand side)? Maybe if the block was originally an automobile engine? Or, maybe the block would normally be used by a different boat builder and would normally have a different cam-chain cover?
I have no idea what the origins of this block are.
Am I being stupid and missing something fundamentally simple?

Any help is greatly appreciated.
 

QBhoy

Fleet Admiral
Joined
Mar 10, 2016
Messages
8,348
Hi

For the price to replace, I’d never trust an old diz in this type of situation.
Mom sure you’re maybe right but 6o before tdc sounds a bit low maybe. Had it in my head it should be 10 or 12o on these. Not sure why.
 

Scott Danforth

Grumpy Vintage Moderator still playing with boats
Staff member
Joined
Jul 23, 2011
Messages
51,191
Pull the timing cover and verify cam timing. Sounds like youre off a tooth on the cam

Use a piston stop to verify TDC

Is this a 1P or 2P RMS block? What was the old block?
 

kenny nunez

Captain
Joined
Jun 20, 2017
Messages
3,437
2X s on what Scott advised. All the AQ Volvo GM engines I worked on had the timing flag on the port side of the timing cover between 1-2 O’clock position. I realize that later model GM engines re-located the timing marks.
It is easy to R&R the timing cover without removing the pan. Cut off the old gasket material and re-seal it with a good grade of RTV.
The Petronics conversion is a good thing to keep. I swapped quite a few over from the points system.
 
Top