Questions on 1558 exhaust valve clearances?

PostPost by: bg109685 » Sun Apr 01, 2012 11:40 pm

Hi All,

My workshop manual states that the cold clearance of exhaust valves in engines to 9951 should be .006in. and .009in. in engines from 9952.

My questions are:

1. What does the 995* number refer to?
2. How can I tell which group my engine sits in?
3. Why is there a difference in the first place?
4. What are the implications of not having the correct setup?
5. After having new (unleaded) valve seats and guides fitted which clearance is correct?

Many thanks
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PostPost by: AussieJohn » Mon Apr 02, 2012 12:25 am

I thought 9-11 was now the norm for standard exhaust cams.
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PostPost by: rgh0 » Wed Apr 04, 2012 11:02 am

bg109685 wrote:Hi All,

My workshop manual states that the cold clearance of exhaust valves in engines to 9951 should be .006in. and .009in. in engines from 9952.

My questions are:

1. What does the 995* number refer to?
2. How can I tell which group my engine sits in?
3. Why is there a difference in the first place?
4. What are the implications of not having the correct setup?
5. After having new (unleaded) valve seats and guides fitted which clearance is correct?

Many thanks


9951 is the engine number but is not relevant anymore as all engines have new valves by now and in any case going to a slighly larger clerance will not hurt.
The change in spec would have been due to a change in exhaust valve material or in the cam acceleration ramps or both.
Too small a clearance can result in the clearance closing up in a hot hard running engine and the valve being held fractionally open and then the valve burning. Too large a clerance that does not match the cam acceleration ramps results in a noisy cam tappet and ultimately premature cam and tappet wear.
Use 10 thou plus and minus 1 thou for any engine now.

cheers
Rohan
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PostPost by: bg109685 » Fri Apr 06, 2012 10:20 pm

Thanks Guys,

Appreciate the wisdom.

I,m the process of putting my head back on the road and looking at the technical data I had a choice :)

It looks like it will be the larger gap this time....

Adios
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