thought some of you might want to see this

That's pretty interesting. So far, I've only rebuilt my S4 turbo engine. I was unaware that the S5 had that threaded or ribbed part or whatever you want to call it in the middle. They also appear to be quite a bit thicker. Are they known to be much stronger/more durable than the S4 parts?

And Cosmo one are even thicker...

Who cares - these things rarely break, so there's no reason to run thicker ones.





-Ted

the ribbing is there to try and reduce a harmonic around 8500rpms, that snaps bolts. the s5's rev higher than the s4's, but they do rarely break, although gtus kevin has broken like 4-5 of them.....

I broke one of those on my old 87 NA about 11 years ago. It was one of the lower ones near the exhaust; can't remember which tension bolt # it was. The flywheel struck it then bent it in a right-angle shape; pretty wicked looking. https://www.nopistons.com/forums/pub...IR#>/smile.png



B

I've seen a picture of a flywheel-raped tension bolt. It bent at a 90º angle.



Some 20B bolts have two ribbed sections.

One of the things I do is put a small layer of Ultra Black or some other RTV silicone around the center part of the bolt to help dampen the vibrations caused at high RPM's. From what I've been told, "it's an old racer's trick". Seems to work well.



B

We're trying to develop a safety plate to prevent damage to the tension bolts if they do back out of the holes.





-Ted

That's a good idea. Will it use the stationary gear bolts to hold it against the tension bolts?

Yep, just like the pics in the H2MY RX-7 book...





-Ted

Anyone ever figure out why Mazda threaded the end of the Bolt so much? It only goes In a fraction of the amount that Is threaded. :confused:

Old bolts had a shorter threaded section. My two R5 13Bs had different lengths of threading. The short threaded bolts had rotor housings with three aluminum outcroppings around the spark plugs. The longer threaded bolts had semi-circle shrouds like FB 12As, which makes me think it's newer. This phenomena is only on the newer engines. https://www.nopistons.com/forums/pub...IR#>/smile.png



As to why, I can only guess that it's to try to prevent snapped bolts during high RPM running. Or they could make only one length of bolts and just chop 20mm from the ends for use in 12As (rather unlikely).

Do you have a picture of this Ted?