Engine Failure

Yes thats the truth of the matter. Rebuilt by me with dino parts cams springs and pistons. It ran on the test bed for 4.5 hours and then ran beautifully for 245 miles, the 246th (spooky) wasn't so good. the engine gradually got noisier (tappety) and sounded what I can only describe as a wooshing noise. Oil and temp fine, with seemingly no loss of power - although I was driving on a very light throttle. When I pulled up at the lights my son actually said 'someones firing a gun at us' - there where two sudden sharp cracks like a rifle going off. Oil and Temp still ok, all still running but getting rougher especially at tickover. I did what any respecting enthusiast would do - shoved it in the garage and went for a drink.
Anyone guessed yet? A week later I pulled the engine and started an aircraft style dissection. Cams fine, shims, fine. Off came the heads. At a quick glance the pistons looked fine albeit very sooty, but on closer inspection four of them had been just lightly touched by something, something bigger than the valves in diameter - yes the seats had come loose - see the smoking gun picture! Its a miracle that everything survived, I now have to strip and check everything but will also need new seats - please. I need to know the proceedures and interferences, because clearly the 'experts' dont.
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Damn.

Had you replaced the seats at the time of the rebuild?

 

yes they had been replaced

 

Man, very depressing....

On the bright side, it was easier to take apart this time..????

 

Nickrry,
I had a new valve guide fitted two years ago and watched the machine shop replace it. Old one was drilled/reamed out close to bronze diameter and then drifted out. Head was warmed up and new valve guide chilled in liquid nitrogen and then tapped in. My guess its similar for the seats.
Kevin

 

If some one replaced this seats for you, they have to repair the engine for you. Take it back if they are a reputable shop they will stand behind their work. I fnot, take them to small claims court.

Seats need an interference fit of 0.003" to 0.005".

Do not!!!!! heat the head beyond 200 F, you will anneal the aluminum and soften it.
do not!!!! let the welder preheat the head for the same reason if the head needs welding.
Do not!!!! use liquid nitrogen as was suggested because the thermal shock is too great and the guide will jump around in the bore and scare the hell out5 of you. Just heat up oil in a frying pan until it smokes and drop a drop of cold water into the oil and watch the fun.
Also, the nitrogen leaches out any oil in the guide and could cause galling of the cylnder head
seat inserts are available from any reputable machine shop.

check the top land of the piston, that's the top ring groove, as the impact could have squeezed down the land and froze the ring in the groove.

good luck
clay

 

Who replaced the seat? Dinoparts?

 

No not dino parts, they have been great throughout, and I have already contacted them with regard to replacing the seats - but things could get very expensive

 

How are you going to ensure correct material and sizing?

Do modern materials and installation methods jive with the original?

 

Don't worry about seat material, early 246 and most 206's used bronze seats which were notorius for falling out, overheating would expand the bronze and upon cooling the bronze would cool and the seat would shrink. Fine for racing applications where overheating was strictly controlled but road car drivers would just drive the car home instead of stopping.

A lot of customers required bronze seats as a replacement and we had to make them special. Nissan tried it on their 240 and a 12 engines with little success and finally gave up. We made a fortune repairing them.

How do you spell notoreus?

clay

 

Bronze(copper)-beryllium is the way to go both for valve seats and guides if you're buidling a serious engine.

 

How do you spell notoreus?

notorious

 

forget the exotic materials and forgo super hard seat materials. Seats that are too hard make the valves bounce at high rpm's. Bronze seats and such alloys are racing only and a lot of racing technologies do not transfer to road cars. The conservative way is the best.

Lastly, unleaded fuel not having the lubricating properties of the old fuel leading to valve/seat failure is a myth. However, very lucrative for my business as muscle car owners and gear heads would be removing their heads for harder seat installations. Good for business.

Lastly, honest, look very carefully at the thermostat, when it opens it must close another water circuit and explore it's function. Get a laser temperature tool to read temperatures at different parts of the heads and block to check for hot spots.

Thanx for the spell check, do we have that function on here?

clay

 

Many thanks for your input guys, I really appreciate it, I am just an amatuer enthusiast who has had an unpleasant experience in spite of trying to do things properly. I have now recovered form the initial shock of the prospect of a second rebuild and am itching to get back at it. My remit is a reliable engine for continental touring with a bit more poke than standard, I will keep you posted of developments. I am determined my Dino 'will be back!'
thanks
Nick

 

We are with you!!!!

 

may the force be with you
clay