Pre Detination

Cole Wilson · Post by **Cole Wilson** » Thu Jun 16, 2005 9:54 am

I have been fighting pre detination (spark knock) in my 303 all summer. I have made many advancements to fix the problem but I can not get rid of it on warm days. I installed a cold air induction an electric fan with shroud, a cooler thermostat, and I have been running 92 octane it all helped but it needs more. I would be happy to here any Ideas. Thanks Cole

TiredIronGRB · Post by **TiredIronGRB** » Thu Jun 16, 2005 1:16 pm

I assume you have worked with the ignition timing before the other mods? Mine does it a little on 89 octane so I always run 93 octane.

George

David Dunn · Post by **David Dunn** » Thu Jun 16, 2005 1:37 pm

You could also have a carbon buildup on the heads and pistons. We use to pour water down the carb a running engine at operating temps, the water would cystallize the carbon and blow it out the exhaust.
Also retard the timing a bit.

Dave Dunn

Lightningpinz · Post by **Lightningpinz** » Thu Jun 16, 2005 2:42 pm

assuming you have no timing adjustment issues or valve adjustment issues and this is detination not preignition, you could have a fire ring (part of the gasket) protruding into the combustion chamber glowing (we have seen 2 occasions) or since the Volvo do not have hardened valve seats the cast iron seat in the head is pocketed and therefore the valve face is also pocketed which gives a hot spot and similar symptoms. Those are a head off. You can contact Dennis for exchange pricing he has them on the shelf.

Now regarding pouring water into the carb. OH MY GAWD! Dribble don't pour. Years ago when I was getting a start, a customer saw one of our mechanics dribbling water into a carb at full throttle. That customer immediately drove home (hot engine) and POURED a cup ful of water into the carb at full throttle. He got a ride back and wanted to sue us because he ruined his engine. Think of thermal shock (he bent most valve stems) and remember water is incompressible at the pressure generated in an engine (4 wheelers who do stream crossing warn against hydolock)
So to de-carbonize do it right or be very careful and dribble don't pour.

Jim Molloy · Post by **Jim Molloy** » Fri Jun 17, 2005 11:44 am

Cole,
I had very similar problems. From the first day of ownership, I had a bit of knock on long uphill climbs in the mountain passes. I tried timing changes that seemed to help a little. Tried lead substitutes and octane boosters with some help...temporarily. Even tried replacement distributor. Things finally declared themselves when I blew a head gasket. Actually, I detonated through a head gasket.

When I pulled the head, I found the metal rim of cylinder #5 pitted over half of its circumference with the ares of erosion into a water passage quite evident. There was significant exhaust valve regression on three of the six cylinders. Two cylinders also had quite a bit of carbon build-up as well. The head was not warped. Since I wanted to eventually run LPG, I opted to have hardened valve seats and new exhaust valves installed in all cylinders.

What a difference!!!

Now, I do not worry about lead substitutes/octane boosers but I still run 92 octane gasoline. The head removal is a very simple task on B30A engiine.

Hope this helps.

Jim Molloy
Waldersee Farm
http://www.northwestmogfest.com
http://www.volvo4x4.cm

Cole Wilson · Post by **Cole Wilson** » Sun Jun 19, 2005 2:16 am

Jim.
I also blew a head gasket with the same description you gave of the gasket. I had hardened seats put in and I am still having the same problem. Have you changed it over to LPG yet I was very interested in this conversion I have heard LPG is about 110 octane.

Jim Molloy · Post by **Jim Molloy** » Sun Jun 19, 2005 2:54 am

Cole,
I have not made the switch to LPG yet. That will likely come after NWMF05. I would explore the timing issue again.

Jim Molloy
Waldersee Farm
http://www.northwestmogfest.com
http://www.volvo4x4.com

rickardp · Post by **rickardp** » Fri Nov 04, 2005 2:50 am

Ive had several Volvo's where the forward timing advance springs inside the distributor were REALLY tired or stuck, both on a B21A and a Volvo Penta AQ130 (B20 in a boat), the latter had corroded so the advance was stuck.

Took me a long time to figure this out the first time (B21A).

At one time I had a Volvo 360 (B19A) that knocked heavily and shot blue smoke out of the exhaust, it turned out to be the crankshaft ventilation (probably not the correct english technical term) that was clogged, a quick replacement and it was a completely new engine.