Bent valves.
 

Hello All,

I sent my valves off to supertech and I received a call from my machinist. Per supertech all my valves were bent. How is this possible?

I did snap a timing belt and shortly after cylinder 3 had an intake valve head that broke and lodged itself into the valve seat. I can understand all valves being bent on cylinder 3 but not remaining valves. The head casting was cleaned up, original valve guides with double supertech springs used. I am wondering if the valves were bent from the start not sure if supertech is being honest with their findings. I did spin all the valves by hand to check for bends only valve that appeared bent was the other intake valve from cylinder 3.

Supertech did offer a discount on new valves and pistons which I got.

Can someone more knowledgeable than I enlighten me on all valves being bent?
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You've probably built an interference engine, which is easy to do on a BP when you change deck height/pistons/valves. All 4 cylinders were probably bent, #3 was just the weakest link that eventually snapped.

I've done this before with BMW engines, although those bend from a mechanical over rev. When I tear those engines down, all 6 intake valves show contact on the pistons, but leak down will show poor results on only 1 or 2 cylinders.

What's the fix, thicker head gasket? It'll be the same block and head going back on. Should I get a new head?

Double check the guides aren't damaged, otherwise you can reuse the head.

The fix for the BMWs is to not over rev it. Likewise, the fix for your setup is don't break a timing belt. They last 100,000+ miles, there's no reason you should be breaking them.

Nothing wrong with an interference engine, I ran them for 10-15 years in a dual duty car and then the racecar. The dual duty car did 100-150k kms with that engine, the racecar ran for 8-9 years with one.

Head is fine (might need new guides though). Time it carefully, don't over-rev it AND ALWAYS USE A NEW TIMING BELT.

Decking the block, machining the head, and high lift aggressive cams are all part of the recipe for a fast atmo BP. If you want power, you have to learn to handle the consequences - its limitations (eg the above three and more), and the fact that you are pushing towards the edge and failures are to be expected from time to time.

How old was your timing belt when it snapped? Like stated above, they don't generally just give up under 100k miles.

Case in point, my recent timing belt failure was due to one of the water pump bolts backing out and making contact with said belt... :loser:

It’s certainly puzzling when all your valves are reported as bent, especially when it seems like only a few should have been affected. Here are a few possibilities to consider:
- Timing Belt Failure Impact
- Inspection Sensitivity
- Secondary Damage

Timing belt probably had 50 miles on it before it snapped. The engine had 104 miles on it before the valve broke.

Is it worth upgrading to the manganese guides?

the builder wants me to get the .060 head gasket. At this point I'm deeply concerned it will happen again I can't keep throwing money at the same exact problem. I'm going to insist the builder triple check his work.

Its pretty easy to check piston to valve clearance...

This^^

But also, I would be heavily investigating why the belt gave out 50 miles in. Sorry if I missed it in another thread but were you running the standard belt or the Gates RPM belt? Not that either should pop within 50 miles of use...

The Gates racing belt, broke right across a grove.

H is the official report. Valves guides were not replaced by the original builder. There was this ticking sound from the initial start up of the car.

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Damn, lost a long post.

I think Supertech get a pass on this one. Either you over-revved it (usually a missed shift), or the shop is the problem. Ticking from moment one is a bad sign, you should have called a halt immediately at that, but that is water under the bridge now.

Why does the shop want to use the thicker HG? All they have to do is time the engine to suit the piston-valve clearance, and you are cool. That is how it is done, assuming you are proceeding as I described above, shooting for a high-output atmo engine. Turbo doesn't normally have to use such measures, if that is the case, why?

Signs are that the shop doesn't know Miata engines, and/or high performance builds. Saying that, I am assuming they handed you a completed engine ready to install?

Did the belt break first or did the valves contact first causing the belt to break?

An acquaintance car had piston to valve contact(I think on an over-rev) and the timing belt(most likely a Gates blue) didnt break, but he destroyed the valves and ended up crushing the ringlands of the piston(found after everything was re-assembled and the motor smoked like a freight train).

The previous builder is more keen on LS and Ford engines. The new shop wants a lower compression ratio he suggested 9:1 compression pistons and thicker head gasket. The ticking did bother me I figured it was the higher spring rate causing it. Yes first shop gave me an assembled engine I just installed the rest (cam gears, timing, valve cover).

Supertech recommends using their valve keepers which the first builder did not use. supertech did give me new valve keepers, valve seals, and valve guides at no charge. I trust this new shop thy have worked on miata engines before. When I do receive the engine back it's going to be peculiar to note if there is no ticking.

I have no idea if the belt broke on its own or contact. I want to say on its own. The belt broke at idle shortly after starting it. I replaced the belt and took it around the block with no issues until the valve broke. The shop is saying there is no signs of the valves touching the pistons. Could have been a faulty belt or it was the kiss of death before the major catastrophic event.

It was a Gates racing belt should I use another brand of belt?

Say what!? The belt broke, you replaced it and the engine ran for some time before grenading? And the replacement belt did not break/was not broken when engine stopped? I think that broken belt should go back to Gates for analysis, and yes, they are the gold standard. I understand you asking the question, but I don't know of a better belt, generally available and affordable lol.

If so, was the ticking present all the time, only before the belt broke, or only after the replacement belt was installed?

Did the engine builder give you any instructions/settings on timing, and did you follow them to the letter? Did the engine builder give you any warnings about valve-piston contact, and how to avoid it? Who sourced/specced the cams? Regardless, it looks like you timed the engine (twice!), so you are pretty much in the gun.