Hi,

Currently rebuilding a crusty VVT engine - see also Build Thread with lots of Pics here https://www.miataturbo.net/build-thr...ebuild-111237/ - and have now been informed by the mechanic that the valve guides should also be replaced when handed over to the machine shop. Lots of play in the valves.
I've attached two short videos to the post.

Now, the destroyed previous NA BP engine rebuilt in 2022/23 had Freccia OE replacement iron aftermarket valve guides. I pulled the destroyed head apart yesterday to inspect the old NA BP valve guides and found some odd scoring in some of the valve guides. Most notably Intake valve 3 & 7.
Also a bit less on some exhaust valves. Lots of marring and ring shaped grooves ?
The intake valves were also pretty damn stuck to the keepers. Valves spring fully compressed and I had to wack the valves from the bottom with a piece of wood and rubber mallet pretty hard to get the valve keepers loose.


Intake Valve 3 from destroyed NA BP Head

Intake Valve 3 from destroyed NA BP Head

Intake Valve 3 from destroyed NA BP Head

Intake Valve 7 from destryoed NA BP Head


Anyone seen valve guide damage like that before ?



Also, for the new VVT valve guides - I'm thinking no iron for the VVT. The only bronze valve guide options with somewhat short term availability in the EU seem to be:

• Supertech - 8 x intake, 8 exhaust
• GSQ - just sets of 8, no distinction between intake and exhaust ?!?

I'm thinking Supertech ?
Will be running OEM cleaned/reground exhaust valves and new hardened Osvat intake valves, stock springs/keepers.


And for main / crank bearings, the previous destroyed NA BP engine had ACL Race.
Should I get ACL street bearings for the VVT rebuild ? Or stay with the ACL Race ?
Engine only sees a couple track day sessions per year, rest street.

 

Knurled valve guides are a thing, so the spriral grooves don't bother me.

Bronze is a common upgrade, so that's good.

 

Yeah I'm not talking about the spiral grooves. I uploaded to full video, maybe it makes more sense that way.
Most bores are clean and have light spiral groove from the reaming / knurling.
But some have obvious damage:
#3 - 00:30 - visible damage
#5 - 01:09 - visible damage / horizontal rings
#6 - 01:27 - light damage / horizontal grooves

Or just a short video of the type of damage im talking about:


I think it might've been from heavy carbon deposits on the valve base riding on the guide, I'll have to check with the corresponding valves when I get back to the engine next weekend.



Meanwhile ordered Supertech bronze valve guides for the new VVT build. Thanks.

 

Also is there a difference between NA BP and VVT BP connecting rods - any benefit from reusing the old NA rods or the newer VVT rods ?