Exhaust valve tappets keep needing adujstment

[71Westy]

So I have my new engine (VWH all-new jobbie) and it's now done 3000 miles. It seems to be running well (but noisy on a tinny german aftermarket exhaust). But 3 of the 4 exhaust valve tappets keep tightening up. Number 3 seems to get wider by a thou or two every 1000 miles. But the others tighten up to little (to 2 or 3 thou) or no gap over 1000 miles. Is this normal for a new engine? And why does number 3 not behave in the same way?

I am adjusting when stone cold (left overnight). I assume running with no gap might elad to exhaust valve issues when hot?

All plugs look good. Running rich on idle but spot on at the cruise. Timing all set correctly.

Thanks.
Nick

 

[Trikky2]

Variations of one or two thou are nothing to worry about.

If on the other hand you set them to .006 and a thousand miles later they have closed up to nearly nothing then I would contact the engine supplier immediately.

 

[bubba dubba]

why would this happen then tricky????

regards............kev

 

[kev mc]

could be a few reasons, but i know some of the cheaper aftermarket heads have a tendency of the valve seats sinking into the head, making the valve clearance tight.

 

[Trikky2]

As posted by kev, faulty manufacture can cause valve seats to move/recess into the head. The only other way clearances can gradually reduce is if the valves are being eroded or the valve stems stretching. Any of these faults need immediate attention before more serious and expensive damage happens.

 

[bubba dubba]

ok thanks for the info, every days a school day as they say,

cheers.............kev

 

[71Westy]

OK - well I've just come back from another long trip. I'll check what they are like now and then contact the manufacturer. I have kept a record of what I have done.

I don't seem to have much luck with engines....

Thanks for the advice,
Nick

 

[71Westy]

The engine guru is going to phone me back, but they are suggesting overheating. If that is true, it's odd that number 3 is the one that doesn't display the symptoms....

It's running at less than 100 degrees at 50mph or below, 105 on the flat fully laden and at 55, up to 110 if its uphill. On my scotland trip, when it was warmer weather, it did creep up to 115 on some long hills. I know that's on the warm side of good. but would that have that effect? And miss out number 3?

Nick

 

[Trikky2]

It does seem to be odd that No.3 is not affected - I cant think of a good reason other than perhapse its running richer or its compression ratio is lower.....

What were the clearances when you checked them after how many miles?

Overheating can indeed cause valve erosion, valve seat recession and valve stem stretching and would be a prime suspect in a case of closing clearances.

If it is overheating then the next question is what is causing it to overheat.

Oil temperature is only a vague guide to engine temperature since its the heads where the heat is - not the sump. This is something I have so far not been able to explain / persuade people about. These engines are air cooled - not oil cooled.

For instance, adding an extra oil cooler will cool the oil but not the engine - its not possible to transfer the extra coolness to the cylinder heads.