stripped valve cover bolt

Hi, I have a 454/330 Mercruiser. I was going to look at the oil leaking (not bad) from the valve covers, maybe tighten them down a little or change the gaskets. I found they were really tight in some places, too tight, and pretty unsnug in others, like someone (the PO) had been fooling around with it.
Ok so far, but one of the bolts, at the rear of the engine on the starboard side, is stripped. It won't tighten, but it seems like it will loosen out, if I'm careful. So, I'm wondering (it's hard to get to, with the exhaust right there) what I can expect to see. What are the chances of it being just the bolt, and not the block that's stripped? If maybe the bolt ws softer than the block? Has this happened to you before? How did you fix it? Thanks, Pal

You're going to have to pull that bolt and inspect the threads. If the bolt threads are buggered up, then first just try replacing the bolt with a new one of the same length and thread. Before running in the new bolt, run a matching threader tap down the hole to clean out the threads. Be sure to measure how far the tap goes in before bottoming out. That will tell you whether you can use a longer bolt or not - most US engines are bored a bit longer than the mating bolt.

If the threads appear serviceable, or the new bolt won't tighten down, then purchase a 1/2 inch longer bolt of the same size and thread and try that - You may need to shim the longer bolt with a couple of flat washers depending on how deep the hole runs based on what you measured with the tap.

If all that fails, then you will have to re-bore and re-tap that hole and install the correct Helicoil (or similar) insert. That will may require you to remove the engine since you stated it was not easily accessable.

Ok so far, but one of the bolts, at the rear of the engine on the starboard side, is stripped. It won't tighten, but it seems like it will loosen out, if I'm careful. So, I'm wondering (it's hard to get to, with the exhaust right there) what I can expect to see. What are the chances of it being just the bolt, and not the block that's stripped? If maybe the bolt ws softer than the block?

Click to expand...

Ayuh,... A couple of things,...

1st off, you need to pull the exhaust manifold Off to swap out the valve cover gaskets,...
There's just No way around it...

2nd, That's the Head, not the Block, that hole is in...
It's a 1/4"-20 hole, 'n it ain't deep enough to use an over-length bolt...
It could be the bolt, or the hole, both are pretty soft, the bolt is grade 2, 'n the head is cast iron...
If the head is stripped, a heli-coil might be an answer...

3rd. Just tightening it Ain't gonna stop yer leak,...
It needs New Gaskets....

Two more thoughts:

You may wanna just loosen the exhaust manifold vs complete removal, especially if its fresh water cooled. A lot will be driven by the clearance available in the engine room. Most of the older Mark IV standard production valve covers will come off without moving the exhaust manifolds though there's very little clearance.

Also, if the threads in the head are not too bad off, consider just chasing out the hole and locktite a stud in the hole.

Hey thank you for all the good ideas. I don't want to change the gasket just now, or deal with taking off the manifolds or even loosening them (it seems difficult?).. So, I'm thinking I'll first take the bolt out. Clean up the hole. Take a "good" bolt from another position (or buy a new bolt) *and try to see if it holds. . If not, Then maybe I'll try cleaning up the hole with a tap, if I can fit it in there next to the manifold. If all that fails The idea of putting a threaded stud in there with locktite would work for now, with a nut on the outside end of the stud to hold the cover down (is that what you meant?)
Then when I'm doing more major work later I could drill it out and timesert or helicoil it.
Timesert has a neat little site with videos of how they work.
When I get to the job I'll tell you all how it went,
Thanks again, Pal

Sounds like a plan. However, Bondo is correct in that the only way you will completely stop the leaking around the gaskets is to replace them.

Yeah, I agree. I have done it a couple of times on cars. Not bad if you have the access. When I look at the manifolds or do some other work like that I'll just replace the gaskets under the valve cover at the same time.

(Another suggestion someone gave me was to clean out the hole, fill it with JBWeld, let it cure, drill it, thread it, and screw in a new bolt.)
Thanks everyone...

For the JB Weld idea to work, the hole will need to be super clean. It sounds like that may be difficult to do.

For the JB Weld idea to work, the hole will need to be super clean. It sounds like that may be difficult to do.[/QUOTE]

Yeah, IF I did it that way I was thinking some brake cleaner might do the trick.
But I was thinking that unless you overdrilled it, the JBweld layer would be very thin after redrilling and threading it, and that might not be so good. But I am still thinking about it, the boat is two hrs away so I can't get out til next weekend.
My first try will be to be "lucky" and clean the hole out, use a new bolt to see what catches (if anything). No harm wishing, eh?
Pal

Let us know how it works out.

If the threads appear serviceable, or the new bolt won't tighten down, then purchase a 1/2 inch longer bolt of the same size and thread and try that - You may need to shim the longer bolt with a couple of flat washers depending on how deep the hole runs based on what you measured with the tap.

hey everyone , I went out today and got the bolt out, and sure enough, (Chawkman) the hole in the head is about a quarter to a half inch deeper/longer than the original bolt was. (But it's still threaded). So the thread down there where the original bolt did'nt touch is still good. So, I bought another bolt , but a quarter inch longer, and tried to get it in, after cleaning up the hole.
But. I couldn't get it to thread. Here's why: The PO had already filled it with some type of goop, which is sort of hardened. So the very beginning of the untouched threading is either full of crap or is damaged. It was dark. I will go back with a steel pick of some type, and some compressed air, some brake cleaner, tap , etc, and try again before I give this plan up and go to the next plan..

Thanks for the feedback. Try working the tap in and out as much as you can. That should help clean it out.

bondo said:

Ayuh,... A couple of things,...

1st off, you need to pull the exhaust manifold Off to swap out the valve cover gaskets,...
There's just No way around it...

2nd, That's the Head, not the Block, that hole is in...
It's a 1/4"-20 hole, 'n it ain't deep enough to use an over-length bolt...
It could be the bolt, or the hole, both are pretty soft, the bolt is grade 2, 'n the head is cast iron...
If the head is stripped, a heli-coil might be an answer...

3rd. Just tightening it Ain't gonna stop yer leak,...
It needs New Gaskets....

Click to expand...

Hello I'm just coming across this now for an issue i have with that back right valve cover bolt. I got access to it with the bolt sitting in the elongated washer to pull it out with a small magnet and some tricky tools. I need to change my valve cover gasket as its leaking from the same corner. I'm aware I said I got it out before recently but without touching the manifold does anyone have a better technique??? that back corner is the only thing keeping this from being a 5-minute job.