Volvo AQ170 detonating

[arfaname]

Hi all,

I am running an AQ170 VP in a 20ft Bertram. I bought the boat with a "rebuilt engine" that had not been water tested. I have had the engine apart to sort out a leaky rear main seal and believe it to have been be rebuilt. The boat has now been run but I can not seem to get the timing right. If I set the timing to the standard 15deg BTD at 2000rpm the engine starts to detonate from about 2000rpm upwards under load. I can retard the timing and get it to run up to 4800rpm with very slight pinging but the timing is way out for this to happen. 28 deg and -2 deg at idle.

The dizzy is the mechanical advance with no vaccuum adv.

Could spring tension on the advance weight being too loose cause this do you think?


Thanks



Sean

 

[Robj]

Re: Volvo AQ170 detonating

Don't know the timing spec for that engine, but I would check you advance weights and springs.

Have a great day

Rob.

 

[arfaname]

Re: Volvo AQ170 detonating

Wow its been a long time as you can see. For some reason us folks in Aus oftenhave dramas getitng on here.

Well things have progressed but not finalised.

I have had the Dizzy checked, recoed and the curve adjusted to pull some timing out of the top and put a little on the bottom. It still pings.

I have changed props. It still pings.

I can adjust a heap of timing out of it and it doesn't ping but it becomes a real slug.

Its running well over all but I cant seem to shake this problem.

I have had the top box apart ont he 270 and found the main drive shaft to have about 10mm play in it from a loose top nut. Could this rattle and sound like pinging at speed but be washed away by reducing timing and in turn power?

I am heading out tomorrow and will run it on 98 RON with an octane booster from a small tank and test on the main tank with standard 98 RON Also. I am taking a fresh set of plugs and will get it warmed up, adjust the timing to standard and run it up to speed allowing it to ping and see what colour the plugs are burning up high.

I have had the carbys reconditioned and have confirmed the jet size is correct at 145 on the triple solex.

I will pull a lead one at a time tomorrow under load when pinging and see if I can isolate it.


Now after all that gents, I am pulling my hair out with this thing. Any ideas from the gurus?


Thanks



Sean

 

[arfaname]

Re: Volvo AQ170 detonating

To add to the thought process:

The engine is supposed to have a 9.5:1 comopression ratio. I do not know what ratio it is running however I do know all cylinders are nearly spot on 160psi compression. Now with a bit of research on the net I have heard of running double head gaskets to bring down compression ratio.

What are your thoughts on this?

How can I tell if my compression is too high?


Thanks


Sean

 

[Howard Sterndrive]

Re: Volvo AQ170 detonating

9.5 engines usually show about 175 psi in my experience.
160 sounds fine.

I think the high octane fuel may be the answer.

How did the problem begin? suddenly? gradual? after new plugs? etc?

 

[zbnutcase]

Re: Volvo AQ170 detonating

These engines DO ping, and the end result is a blown head gasket. Had a customer with one of these and when I replaced the second head gasket I put an advance timing light on it and discovered the dist was allowing 52 deg of total advance! A simple recurve job for 38 total ended the gasket blowing. Volvo also offered a thicker gasket to reduce compression, not sure if its still available. 'nutcase

 

[arfaname]

Re: Volvo AQ170 detonating

Thanks for the replies gents..

Well I think your both correct after todays efforts.

I have confirmed the plugs are burning well at full revs.

The engine will no longer run well on factory timing settings.

The remapped dizzy has done what it is supposed to.

I adjusted the distributor whilst under way flat out to just below hearing it ping and then back a bit until I lost some performance. Up a deg or two and there it sat.

The main tank runs 98 ron fuel and I took a second tank with 98 ron and a heap of octane booster. When I swapped over the tank and was convinced the fuel had run through i advanced the distributor at least another 5 degrees before it was pinging. The octane booster has me thinking that with a compression reduction I could run standard fuel but I guess I may also lose some performance. Now THAT I cant afford to lose.

So back to the just below ping setting it went and ran the rest of the day well. I did find its running a little hotter than Id like but I have put a 70 odd deg thermostat in it earlier. I will swap it back to the standard 55 deg. it was hard to start when hot.



Summary:

The old engine designed to run on leaded fuel does not like todays fuels. By remapping the dizzy and increasing the octane rating I have eliminated the ping. In doing this I may have lost some power. I am unsure. The end result is a clean running engine that if anything is slightly detuned and should last well. The engine must be run on premium unleaded.



Howard, the boat was bought with a rebuilt engine but the project was unfinished. I managed to get her to run before I bought it with a little bit of mucking around. it sounded sweet on the trailer. It has taken me plenty of hours to get it right. But its such a sweet looking boat I just love it. its all worth it.


Thanks again gents.



Sean