View Full Version : Cracked exhaust manifold
04-28-2005, 05:15 PM
Dewinterized the Prostar ('91, Indmar 351) recently...Fired right up and ran nicely. That's when I noticed a small drip on the port manifold, right under the drain plug. :eek:
Figured it might be the plug itself, but upon closer observation the manifold appears to be cracked along a casting mark near the plug. Looked at the other manifold, and found the same apparent crack, but no leaking.
Question is--are these manifolds definitely done for? I believe the theory is that the jackets might be leaking internally also, potentially leading to a hydrolocked cylinder at start up.
I've got my finger on the button to order replacements (related question--Are these "OSCO" brand manifolds any good?), but am curious to see what someone w/ some first hand experience thinks.
04-28-2005, 05:17 PM
Sorry to hear of you misfortune.
east tx skier
04-28-2005, 05:17 PM
Is it the manifold or the riser? BriEOD just replaced a manifold a few weeks ago. Don't know if JB Weld could patch it. I'd be leary.
04-28-2005, 05:18 PM
I have one of those on my 89 Tristar that I am restoring. They tell me it's only 4 bolts. skidim has them for like $160 or so.
04-28-2005, 05:31 PM
My welder buddy patch welded the cast iron manifold for another friends 89 prostar last month. same thing, only one side leaked. welder grinded 1/8 inch deep and wide groove down crack, drilled pin hole at each end, heated the whole manifold glowing red, laid down a bead w/ nickel rod, kept the whole thing glowing w/ torch before, during and just after welding, then let the whole thing cool down at same rate to keep from cracking. He looked like he knew what he was doing, so far, works like a hose. no leaks. If it was my boat, I would've bot a new manifold, but if money is tight it can be done.
04-28-2005, 05:34 PM
Another thing, we fabbed up a piece of flat plate to bolt onto the manifold to pressure test for interal leaks w/ the jackets you refer to. My bud never even used it. His boat has been working great since the cast iron weld job.
04-28-2005, 05:38 PM
osco manifolds are great, none on my current boat, but great results from past boats and friends. and to the welding, if done correctly, as it sounds like your friend had done, then it would be okay, i would just be cautions about the jacket leaking further in where its not easy to see.
I think after this season i'll be replacing both risers and manifolds for good measure, those things get pretty rusty and corroded.
04-28-2005, 05:38 PM
Yes, I did. I had a small drip last season that I tried patching, etc. Obviously, it wasn't going to work again. I ordered a new manifold from DIM (skidim.com) and with shipping and the gaskets for the riser and block it was likw $210 (for one manifold).
04-28-2005, 06:33 PM
My welder buddy patch welded the cast iron manifold for another friends 89 prostar last month. same thing, only one side leaked. welder grinded 1/8 inch deep and wide groove down crack, drilled pin hole at each end, heated the whole manifold glowing red, laid down a bead w/ nickel rod, kept the whole thing glowing w/ torch before, during and just after welding, then let the whole thing cool down at same rate to keep from cracking. He looked like he knew what he was doing, so far, works like a hose. no leaks. If it was my boat, I would've bot a new manifold, but if money is tight it can be done.A good welder can resolve the problem as described by Planoboy. I had the (almost) exact thing happen and resolved in the same manner. I'd have the welder to preheat the area within 1" of the repair, to (min) 250 deg. F and lay the bead (in the well described joint prep). Let her cool after the bead is completed. Post weld heat treatment is not necessarily required for this material but it can't hurt. Done deal.
Dam - I just chucked both mine from my '87 into the recycle. I found them for about 175 delivered and would have to do some digging to remember the site. Ended up finding them local for about 150 a side. The only tricky part to the whole replacement job is the riser bolts. 2 of them are tucked in there pretty tight.
04-29-2005, 01:30 AM
Are these freeze damages? or
My LX470 has clicking sound at start up, sometimes, that sounds like lifter going weak, but on the Lexus message board there is a lot of talk about this is actually cracked exhaust manifolds and the sound stops within minute or so when the manifold heats up and the crack seals. From that I would believe they just crack sometimes.
04-29-2005, 03:23 AM
Doesn't sound like a good thing to "just have a crack sometimes" especially on a boat the caliber of a MC!
04-29-2005, 06:58 AM
The manifolds were drained thoroughly prior to storage. Looking at the crack on the non leaking side, it appears to have been painted over at some point, so I'm assuming this is damage from the prior owner (no leakage last year, though.)
There was plenty of scale which I cleaned out when these were drained, so maybe it's just this set's time. Hopefully the risers are ok.