Guys,

During my tinkering this winter, after pulling the engine to fix a coolant leak I couldn't get to while the engine was in the boat, I discovered that I was getting some coolant past the head bolts. I ordered a new set of Fel-Pro TTY head bolts and set to swapping them out. After snapping one of them off before it ever reached torque (I got it out easy enough, and I've since been informed that Fel-Pro stuff has been crap the last couple years), I acquired a set of ARP head bolts (not studs) from Raylar. I didn't really notice until I was in the install process, but they are measurably shorter than the TTY bolts that came out (and the Fel-Pros, for that matter). I contacted Larry at Raylar, who indicated that he'd never encountered a failure, but he also indicated he doesn't deal much with the iron heads, and I can't seem to get a straight answer if the aluminum heads use shorter bolts or not. Near as I can tell, at "finger tight", I've got ~10mm of thread engagement with all but the two mid-length bolts that are at either end of the heads, which are probably close to 15mm. They torqued just fine, but that thread engagement is scratching at the back of my neck. I don't think the bolts themselves are going to fail, but I'd really hate to have them rip the threads out of the block. For reference, originally a Merc 496, now 503ci (by my math), Raylar BP211 cam, roller rockers, M1 ProCharger pulleyed to an estimated ~6psi. Thoughts?

Thanks. Brad.

rule of thumb,bolt dia wants at least that much of thread contact.

Sutphen,

At least. My rule of thumb has always been 1-1/2X the thread diameter, depending on thread pitch. But I wanted to get some insight from some who’ve built engines. I certainly don’t fit that description.

Upon review of my emails with Raylar, I believe it’s only the longest of the three bolt lengths that are short. I’ll need to pull one of each of the three different length bolts out and Make sure. My thinking is that I received 90mm length bolts instead of the 100mm bolts that ARP sells. I can also compare them to the FelPros and OEMs I have here. This block has the tapped head bolt holes breaking into coolant passages (which is how we got here, BTW), so a little longer than OEM (103mm is spec) is OK, and I can use spacers if the “grip length” is too long (threaded length is too short). I’d sure like to use the entirety of the threads in the block if I can make that happen.

I spoke with ARP today. They sell these bolts in 10mm increments in 5packs. I should be able to get what I need if I don’t already have it.

Thanks. Brad.

I've lost count on how many engines I've built.fun fact,arp bolts on a 454 salt water motor in 1 season would be eaten away to have 1/2-5/8" of thread left when pulled.the stock gm bolts,they would be fine for 3 seasons.

Sutphen,

The OEMs were plated with nickel or zinc, probably.

And this is why, when we were looking for our boat, if it was anywhere near salt water, it was an immediate swipe left. Just…. Nope.

Thanks. Brad.

Guys,

So.... Some discovery....

I pulled one of each length head bolts and measured them. The long ones, which make up the bulk of them, are 100mm long, which is as long as ARP offers. The mid-length ones are 90mm long, which is actually slightly longer than they need to be. The short ones are 50mm long. They all have washers under them that are all but 2mm thick. The Fel-Pros I have here are spec'd at 103, 86 and 52, respectively, but don't include the washers. I am going to call ARP and see if they offer 110mm long bolts, but I'm doubting it, since they aren't in their catalogue. Assuming they don't....

What's the best course of action? Remove the washers and go with it? I'm inclined to order two 5packs of the 60mm long bolts to replace the short ones. I can always double up the washers if I run out of threads, and I don't have to worry about the threads bottoming out, since the holes break into coolant passages. I'm fairly spooked by the TTY bolts, having snapped one of them off already; I don't want to have to pull the heads again. There's just too much disassembly that goes with that if I can avoid it.

It was also suggested I go with bolts from Caterpillar, 110mm UHL, which spec to 170K tensile strength, vs ARP's 180K; still plenty strong enough. I'm thinking I'd be willing to give up minimal tensile strength to gain thread engagement in cast iron.

Thoughts?

Thanks. Brad.

Guys,

I made an executive decision. I ordered 60mm long bolts from ARP, and 110mm long bolts from Caterpillar. This will satisfy my concern with head bolt thread engagement. They will be in tomorrow. So I have questions….

The engine is all but together. I have to remove the exhaust rockers to gain access to the head bolts under them, but the intake rockers can remain. Which is a good thing, because I can’t really get to the intake pushrods to feel them as I “zero-lash” the rocker after putting them back on. My plan is to replace the bolts, one at a time, torquing each one as I go. Is this OK? Or should I just commit to it, pull the intake and all the rockers, and go through the whole process over again?

Thanks. Brad.

just change one at a time, shouldnt be an issue with it. I have done that before and not had a problem.

Just curious what you were torquing them to ?? I have never had a problem with a Fel Pro head bolt.

Brad, can you describe what and how and where the head bolt broke?