Bugeye valve rebuild suggestions

[ichthos]

Been a while since I have been on the forum. It is good to be back. I am not sure yet, but I am suspecting my valves need to be rebuilt. Hoping to do a leak down test when I get my tester from Amazon. in the mean time, I need some specific pointers on what to ask for when I get my valves rebuilt. I have the original 948 engine. Do modifications need to be made for the newer unleaded fuel? Any help would be greatly appreciated.

 

[DrEntropy]

Well! 'bout time we saw yer "face" again!!

Best suggestion I can make is be sure you have a machinist who won't treat it as if it was a lawnmower.

A "three-angle cut" seat would be one thing to ask for, and a VERY slight shaving of the head ONLY if it has been checked for warpage and some is found. Have the valve faces and stems checked for wear, replace if any is found. Replace the valve guides, new seals & springs as well.

Other stuff not necessarily machine work, will be to check rocker shaft and rocker arm bushings. Shaft wear is usually easily spotted, replacements are available. If bushings are out-of-round they should be replaced, but need to be reamed after being pressed in, so that's best done by a machinist.

As for the valve seats, pros and cons for inserts are wide ranging. Never found the real need to fly-cut and insert seats in the BMC heads, though.
A good treatise on the subject HERE.

Those are my off-the-top thoughts. Hopefully others can think of anything I've missed, and some may disagree over the three-angle seat suggestion.

 

[JPSmit]

certainly worth making sure it is set for unleaded gas while you are at it (Is this the valve seats bit doc?) - I also wouldn't overthink it - years ago I was listening to Click and Clack on Car Talk - I don;t remember the issue but, one says 'you need a good mechanic' - and the other bursts in with; 'no, you need an old mechanic!'

Ask around and find an experienced engine shop in the area that does classics...... My local shop did a great job on mine (Vauxhall) and yet it was likely the only Vauxhall he has ever done - or ship it to Hap Waldrop.

 

[ichthos]

Thanks for the specific tips. So, what is it that normally has to be upgraded for unleaded fuel specifically?

 

[DrEntropy]

Some folks are hung up on fly-cutting the cast iron head to put "hardened" valve seat inserts in. Been my experience that is not necessary, just run it on the highest grade fuel you can find, 90+ octane.

Having valve seats inserted is costly, machinists with enough experience to do it correctly are becoming harder to find. If done incorrectly (it's an interference fit) an insert can drop out and trash head, piston & bore. IMHO not worth the time and expense to take the risk.

 

[drooartz]

Good to see you back around!

 

[ichthos]

Maybe someone can clarify this for me. They used to add tetraethyl lead for an octane booster. I thought the byproduct, lead, lubricated the valves. Is this information correct? i already use ethanol free gas, but how does running higher octane help?

 

[DrEntropy]

Maybe someone can clarify this for me. They used to add tetraethyl lead for an octane booster. I thought the byproduct, lead, lubricated the valves. Is this information correct? i already use ethanol free gas, but how does running higher octane help?

Yes, lead additive was to somewhat lubricate the valves. Ethanol changes the burn characteristics of the "bang" and also lowers the "octane" level. That's the short version.

Using the highest "octane" rating available at the pumps helps keep pre-detonation from occurring.

 

[SaxMan]

I run 93 octane in my Sprite and have never had any kind of detonation issues. I think hardened valves are more critical on engines that have compression ratios above 10:1 like many muscle cars.

Another option is to go to your local airport and purchase 100 Low Lead aviation fuel. A lot of the airplane guys are recommending I do that with my Sprite prior to winter hibernation as 100 LL has a 10 year shelf life, far in excess of any kind of automobile pump gas.