When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
Engine Mechanical TopicsDiscussion for motor builds, cams, head work, stripped bolts and other engine related issues. The good and the bad. If it goes round and around or up and down, post it here.
To start, no, this was definitely not me overtightening the intake manifold bolt. I bought this bike used (1999 FXDX), a previous owner installed the Screamin Eagle intake manifold before me and they utilized 2 hex bolts on the left side of the bike vs the factory allen bolts (which I know is a common thing to do).
This bike had an intake leak (possibly because of the problem bolt not being torqued properly), so, today I went to replace the intake seals.
One of those bolts came out harder than I would have liked. Went to install the manifold, creeping up slowly on all the bolts evenly (I know those bolts are only 16 ft lbs). I came no where close to the torque spec and it pulled the threads on that one bolt hole.
I'm thinking I can helicoil it with a stubby drill bit. I won't be able to fit a drill in there; would I be able to drill out by hand (small tapping wrench)? It will need a 5/16-18 helicoil.
If anyone has a better idea please let me know. I don't want to have to take the head off!
Picture attached
Last edited by garystaven88; Apr 19, 2026 at 09:13 PM.
To start, no, this was definitely not me overtightening the intake manifold bolt. I bought this bike used (1999 FXDX), a previous owner installed the Screamin Eagle intake manifold before me and they utilized 2 hex bolts on the left side of the bike vs the factory allen bolts (which I know is a common thing to do).
This bike had an intake leak (possibly because of the problem bolt not being torqued properly), so, today I went to replace the intake seals.
One of those bolts came out harder than I would have liked. Went to install the manifold, creeping up slowly on all the bolts evenly (I know those bolts are only 16 ft lbs). I came no where close to the torque spec and it pulled the threads on that one bolt hole.
I'm thinking I can helicoil it with a stubby drill bit. I won't be able to fit a drill in there; would I be able to drill out by hand (small tapping wrench)? It will need a 5/16-18 helicoil.
If anyone has a better idea please let me know. I don't want to have to take the head off!
Picture attached
Looks like there's some good threads left down in the hole. You may be able to either use a longer bolt or use a stud and bottom it out when you install it. If there's enough room, use a flange nut on the stud to secure the intake manifold. I never use a torque wrench when installing an intake manifold. I snug up the fasteners nice and even and that's it.
... a previous owner installed the Screamin Eagle intake manifold before me and they utilized 2 hex bolts on the left side of the bike vs the factory allen bolts
...
Were the replacement bolts shorter than the original?
Were the replacement bolts shorter than the original?
Looks like they were. There is about 4-5 threads gone. The screw is 5/16-18, so it about 1/4 inch of threads and 1/4 inch for the manifold clamp which means the bolt was likely 1/2 inch long. The stock screws are 3/4. Looking at the head, you can see where the ring slot dug into the head. Chances are that it was severely over torqued and the rings may be bent.
Might get a longer screw in but stock should work and they only need torquing to 8-10 fp.. Add a little high temp blue.. OP can try a tap or thread chaser but the clearance are close if the other head is still on.
Looks like they were. There is about 4-5 threads gone. The screw is 5/16-18, so it about 1/4 inch of threads and 1/4 inch for the manifold clamp which means the bolt was likely 1/2 inch long. The stock screws are 3/4. Looking at the head, you can see where the ring slot dug into the head. Chances are that it was severely over torqued and the rings may be bent.
Might get a longer screw in but stock should work and they only need torquing to 8-10 fp.. Add a little high temp blue.. OP can try a tap or thread chaser but the clearance are close if the other head is still on.
The bolts are all 3/4" long so not sure what happened there. Again, I evenly and carefully tightened each one a bit at a time. I'm guessing those threads were already jacked up from another person who installed that intake years ago. It didn't feel good when I removed it.
I bought a 1" long bolt and it worked perfectly. Plenty of room before it hits the wall of the blind hole.
Runs much better without intake leaks!
Original seal deterioration Vacuum plug on Mikuni deterioration
Last edited by garystaven88; Apr 20, 2026 at 11:57 AM.
7 Surprising Harley-Davidson Products that Are Not Motorcycles
Slideshow: The bar-and-shield logo shows up on far more than motorcycles, some of the company's most unexpected products have nothing to do with riding.
Slideshow: From the troubled AMF years to modern misfires, these bikes earned reputations for reliability issues, questionable engineering, or disappointing performance.
Crazy Bunderbike Build Looks Amazing, But Is It Impossible to Ride?
Slideshow: The Swiss custom shop has taken a Harley Softail and stretched it into something so long and low that it looks closer to a rolling sculpture than a conventional motorcycle.
Engraved Rebellion: Inside Bundnerbike's Glam Rock II
Slideshow: A standard cruiser becomes an intricate metal canvas in the hands of a Swiss custom house known for pushing Harley-Davidson platforms far beyond their factory brief.
Slideshow: Harley-Davidson's challenges aren't abstract; they show up in dropping shipments, shrinking dealer traffic, and strategic decisions that aren't yet translating into growth.
Stripped TC88 Intake Manifold Threads
