Well, if it were me I'd check the valve-to-piston clearance before bolting it all back together.

--Ian

 

What is the best way to check the piston to valve clearance? I'm reading about it now, but I see there are multiple ways to do it.

 

the best way ive seen is with a degree wheel and those like super light valve springs.

 

I love Jafromobile's videos. They're all really informative, but entertaining enough that I can watch 30 minutes straight of it.

 

If you're just trying to validate that it's a non-interference engine and never hits, then I think the best way to do it is with clay.

If you're trying to measure how much it interferes and where, so that you can adjust cam timing/etc, then you need degree wheels and something fancier.

--Ian

 

Thanks for the replies. I don't know which method I'll do, but definitely going to do one of the two suggested. If I remember right, the exhaust valves do hit on this motor at high lift with the piston at TDC, but that scenario should never happen with the cams timed correctly. I think I'll do it the degree wheel way to see if the valves are just too close or something. Guess I need a degree wheel...

 

any evidence of impact on the pistons?

 

The clay method is easy peasy.

Apply clay to the top of the pistons, install cylinder head, cams, and timing belt. Spin motor by hand at least one full rotation. Remove cylinder head and remove clay from piston. Cut the clay in half so you can measure the thinnest portion, or the very least see how close you are.

 

There has been some evidence lately that suggests the later BPs are not non-interference

 

Not knowing if this is right or not...

but wouldn't you want the be at TDC with the timing belt off and then rotate the cam alone with the clay method to determine if it is non-interference?

also, what additional spring compression should you add due to the valve velocity at 8k RPM? That will compress the spring more, might be insignificant.

 

if you are pretty sure the motor is noninterference regardless of cam timing yes, you could do it that way to see by how much. However, some motors are only non interference if the cam timing is correct. Once a belt breaks or is removed, it becomes interference. Then there are cases where large pistons and high lift cams cause interference even if the cam is timed correctly. If you are trying an exotic combination, clearances must be checked.

How much spring you need depends on a few factors; RPM, valvetrain weight, boost pressure, and sustained high rpm periods.

 

I can't see anything on the pistons, they look fine. They have a light coat of oil/carbon that all used pistons have, I guess I can wipe that off and then see if there's anything to see that indicates contact. I'll do that and report back.

Yeah, I saw my old post in that thread where I said it was possible for the exhaust valves to contact my pistons. Hmm. So either I bent them "discovering" they could hit a long long time ago, or they floated there way into contact with the pistons. Maybe I need more valve spring if I'm going to rev to 9K. But with the auto, I'm currently at 8K redline, which I think may stay there and the absolute highest I would ever go with the auto is 8,500 as that's the limit according to PA who built the auto.

The engine is still in the car so using a degree wheel is possible, but more of a pain than if the engine was out of the car. I may do the clay method first, and go from there. I guess I need to see "how close" the valves ever get to the piston during normal operation. I have no idea what the minimum is, and apparently that's an important number that I should have checked.

Thanks again for all the replies, this has me looking and reading several differnet things and watching those vids Aidan linked which are pretty damn good.

 

Correct me if I am wrong, but doesn't non-interference by definition mean that the valves don't contact the piston, regardless of cam timing?

 

You are correct.

Non-interference: Valves and pistons cannot contact each other, even if the timing belt breaks it will not damage anything. Factory NA/NB motors are this way.

Interference: Valves and pistons are kept from hitting each other by being correctly timed, a broken timing belt will cause major damage. Most other engines are like this.

An engine where the valves and pistons hit each other even when it everything was timed correctly would be called a "broken" engine.

--Ian

 

I believe the NB engines are interference. I personally wrecked the valves on an NB that had an improper timing belt job done.

 

Factory NB motors are not interference at normal speeds, if you take the timing belt off then you can put the piston at TDC and then spin the cam all the way around and nothing will contact.

Rev it up high enough to float the valves out of contact with the cams and that might be another story.

--Ian

 

If the valves contacted the pistons, you should see a shiny spot without cleaning them. should not need cleaning to verify. How did the seats look? I have seen valves bend when they have excessive slop in the guides. that allows the valve to contact the seat unevenly. I imagine that is a possibility since you have springs with high seat pressure a high rev limit.

 

I did not disassemble the head to inspect the seats, I just brought it to the machinist that built my bottom end that's taken 40 PSI boost without failure. I tried to look at the exhaust seats on whatever valves were open from the cams holding them partially open. They looked like seats, I could still see all the angles machined, but that's about it. Couldn't see but one area of the seat without taking it apart. I'll ask the machine shop if they remember how the seats looked when I pick it up.

The pistons look fine, I inspected them carefully and can see no contact. I will clean them and check again.

I'm hoping/thinking the loose guides may have caused the valve to bend as you say, but I don't know that.

 

Also ordered larger washers for the ARP studs. I was previously using the stock miata washers torqued to 65 ft*lbs. I found some larger ARP washers and ordered those. Math says the new washers have 24% more area than the stock washers, so that should help spread the load across the head bolt boss without cracking or denting it. ARP are thicker too and ground flat vs miata washers are thinner and stamped with rounded edges. I think I'm going to up the head bolt torque so this will be a good idea. I also ordered some parts to build a current sensing monitor for the rear oil pump. When this is done, I will have a red light that turns on if that pump ever fails to pull the "normal" amount of current I tell it to look for.

Other than that, the car will be sitting till the ARP washers are here and the head is ready.

 

Got a part number for those washers?