How often do Main Studs and/or Rod Bolts REALLY fail?

[Shytheed Dumas]

I'm ready to take my block to the machine shop, but I need to decide whether I'm going to reuse the stock studs/bolts or upgrade to ARP's. In the end it boils down to assuming risk of failure on the stockers, but I need to know what the risk actually is - especially at 350 to 400 whp.

Who has had stock main studs or rod bolts fail and with what mods/hp? How 'used' were they when they failed? Has anybody ever had ARP's fail? (doubtful, but worth asking )

I've heard all of the 'if you're gonna do it, do it right; do it big; do it whatever and go with ARP arguments. That's a great philosophy, but if there have only ever been three failures in the history of the 7M and they were on engines with 250k+ miles and 650 whp, then it's a needless $200 overkill. On the other hand, if 20% of engines built to 400 hp fail due to studs/bolts, then that's another story and definitely worth the money.

Over the past couple of years, I'm not sure I've ever seen a thread started because of failed studs or bolts, so lets see what the reality is.

 

[drjonez]

from engine tq (hp)? never. no one has ever found the tq limit of stock rods or bolts. based on what milbrum has seen, the crank does go a bit funny around 1.2krwhp...

mains? never.

the stock rod bolts will go fairly soon if you spin it much past 7k.

 

[Shytheed Dumas]

So at "only" 400 hp and not trying to run higher engine speeds there aren't any known cases of failure due to reusing stock studs/bolts? That's what I suspected...

I was planning on running stock cams and maybe upgrading the valve springs, but no higher revs.

If the mains are not known to fail at all, I might just consider upgrading to the ARP rod bolts since they are pretty reasonably priced.

 

[starscream5000]

Going with the Comp Cams spring upgrade Curt?

 

[drjonez]

So at "only" 400 hp and not trying to run higher engine speeds there aren't any known cases of failure due to reusing stock studs/bolts? That's what I suspected...

I was planning on running stock cams and maybe upgrading the valve springs, but no higher revs.

If the mains are not known to fail at all, I might just consider upgrading to the ARP rod bolts since they are pretty reasonably priced.

i'd say so.

i'm on REUSED rod and main bolts.....500 rwhp +/- 7k RPM for 4? yrs...

 

[Shytheed Dumas]

Going with the Comp Cams spring upgrade Curt?

Yessir, definitely considering it.

Thanks Doc - that was just the input I was looking for. :bigthumb:

 

[suprahero]

I was going to give my imput, but Dr. Jonez took the words right out of my mouth..........

Kurt, go big or go home...........:biglaugh:

 

[Shytheed Dumas]

Instead of starting a new thread, can sombody tell me anything about Mahle piston rings? Good, bad, worth it, don't even think about it? It ain't going big like JE, Jay, but at least they're not ebay cheapies either.

Check 'em out: http://www.horsepowerfreaks.com/price/Toyota/Supra_86-92/Mahle/Engine/Piston_Rings

 

[Doward]

Mahle's been around a while, and is (imho) a good company.

Those say 86mm tho (stock in a 7M is 83mm)

 

[Motofool]

i can vouch for mahle's in the DSM community pretty heavily used units

 

[IJ.]

I used Mahle's in my Twin Turbo 4v, great quality pistons and rings.

 

[quake]

i will agree with most of what Dr. jones said, but the stock bolts are tty bolts so they strech. This alone makes me want to replace then as they are designed to be replaced after each use. Now the reality is they never really get replaced on a standard build, but this is usually for standard use.


Now to the point have one fail probably not but the real question is do you want to spend the time money and labor on a rebuild then rely on probability... no you don't not for 50$ worth of rod bolts


p.s. you must have the rods resized after canging the bolts
if you must keep cost down keep the mains (we have 7 caps)

 

[suprahero]

p.s. you must have the rods resized after canging the bolts

What exactly does this mean? I plan on buying ARP bolts for my wife's rods so why do I have to have them resized? I'm not an engine builder so I'm confused by your statement.

 

[IJ.]

J: When they press the new bolts in it can deform the hole slightly.

To "resize" them they take a skim off the parting line of the Rod Cap to make the hold smaller then either Bore and Hone or just Hone to size (B&H is in extreme cases)

All this gives you a big end hole that's round and the correct size.

 

[suprahero]

Thanks IJ.

 

[WhtMa71]

Mahle builds the Realtime Racing TSX and RSX motors for the Speed World Challenge Touring cars, so id say they make good shit. Their pistons are used in a lot of all motor honda builds as well and get very high marks. Id imagine their rings are good.

 

[aljordan]

Instead of starting a new thread, can sombody tell me anything about Mahle piston rings? Good, bad, worth it, don't even think about it? It ain't going big like JE, Jay, but at least they're not ebay cheapies either.

Check 'em out: http://www.horsepowerfreaks.com/price/Toyota/Supra_86-92/Mahle/Engine/Piston_Rings

You should use whatever rings your piston manufacturer specifies.

 

[supraguy@aol]

Going with the Comp Cams spring upgrade Curt?

I did- it's a bargain upgrade.

i'd say so.

i'm on REUSED rod and main bolts.....500 rwhp +/- 7k RPM for 4? yrs...

This is reassuring.