help needed from expert engine builders

[70herald]

There are a bunch of expert engine builders here so let me know what to do.

I got my engine head back and taking a look at it I noticed that several of the springs / valves (all the exhaust) appeared higher than the others. pushing down on the valve (with my calibrated thumb), it is clear that the spring is not generating enough pressure.
According to Bentley, the fitted length should be either (a Herald 1200)1.36" w/27 to 30lbs load or 1.07" with 117lbs load (spitfire) Presumably the difference is a more aggressive cam on the spit??

In any case, the exhaust spring installed length is closer to 1.5" and way below 30lbs of force. squeezing the springs against the bathroom scale showed that if they are compressed to the correct length (whatever that is), the load generated will be correct. (springs are new)

Now as I understand it, I need to add shims. Where exactly do they go? under the bottom spring collar ? between the collar and the spring?

Clearly if they go under the lower collar they need to hardened. Can I just use "standard" washers and put them between the spring and bottom collar?

Thx Yisrael

 

[TheSearcherMan]

Well, it sounds like the valve seats are not right. The valve is cut to deep into the seat. I'm not an expert on this, but it should be closer than .140. I would take it back to the machine shop, and talk to them about this. Also, the reason the exhaust are different, the machinist most likely only changed the exhaust seats for unleaded fuel, and the stock intake seats are still there. So, maybe, he did not install and grind the exhaust valves and seats for the correct spring height.

 

[Brosky]

I agree with Searcher.

You have the specs and they don't match the head. I would go right back to the machine shop with the head. I would ask them what they used as a reference for their work. If the exhaust seat is not the proper width, either too narrow or too wide, the results will be less than desirable.

 

[Guest]

It seems that the machine shop did sub-standard work, or did not use a reliable reference. Fortunately, you caught it. I concur with the others that you should return post-haste to the machine shop for a meeting of minds... The only acceptable response from them AFAIC, is an apology and heel-clicking service to make it correct. I use a very good machine shop here in Houston... but there are many bozo ones here, too.....and it took me a long time to find this one! I pass up 3 others to get to this one! :smirk:

 

[70herald]

There is a difference in the depth that the valve seats were cut. The exhaust valves were cut slightly deeper than the intake and that explains the difference in valve stem height,
However the manual clearly allows the seats to be enlarged by cutting (in order to reduce seat width) at a 15°angle and then cutting a new 45° seat. The depth the machine shop cut is within the spec. The valves are certainly not recessed 0.14" and the manual shows that a very small recess is acceptable.

I kind of wonder if either the top / bottom spring retainers or collets were swapped for something different??? or maybe something else was modified somewhere along the line. In any case I need some sort of solution here, and I am getting kind of frustrated with this car. It has driven even less than cripty and the amount of money I have tossed away on the project is way out of control.