best temporary bodge for stripped engine case thread?

Paul LeClair

Administrator
Staff member
my 1957 Gilera 150 is finished, running, and passed mechancial inspection for registration. As I start the break in and dialing in process, one of the engine case bolts that holds the split cases together has pulled its threads and the engine case now has a small oil leak from the bottom of the motor. When I built the motor I thought I had dealt with all the suspect threads, and I have a total of 9 KeenSerts installed, all installed with the motor completely apart.

I can't see how I could install a KeenSert in the intact engine case, and I need a temporay solution as the engine will likely have to come back out and cases split to properly repair the stripped engine case bolt hole. http://www.repairengineering.com/keensert.html

so, I need suggestions as to a temporary solution to be able to run the bike for the sumemr and in the Moto Giro as I don't want to deal with stripping the engine until the winter.

ideas?
 

Andy

Hero member
I’ve used UNC in the past, as a temporary. Depending on the size of the original the imperial is just slightly bigger allowing you to thread into clean metal, without interfering with the future repair.
 

Dellortoman

Hero member
Is the thread in a lug that you can drill right through? If so, then drill it through and use a longer bolt with a nut. You'll still have enough metal to fit an insert next time you have it apart.

You can also do a bodge by poking a few small strands of copper wire into the threaded part. The soft copper mashes into what's left of the thread and gives the bolt thread something to bite on. It's described in this video:


The guy makes it look easy because he's demonstrating it in a bare hole. It's a little trickier when you're working through the hole in the non-threaded part that bolts up to it, but still do-able.
 

tribonnie

Junior member
Location
uk
If it is a blind hole, squirt out with carb/brake cleaner, then a small amount of “chemical metal” in the hole and on the screw a and refit the screw before it sets. When you come to rebuild use some heat to ease the screw out.
 

Paul LeClair

Administrator
Staff member
Loctite do make a product that 'reforms' a thread in a blind hole.
Never used it , may be worth investigating.
Andy
looked at the Loctite and Permatex Form a Thread Products. They claim like 120 foot pounds of holding power, but when you read the fine print for like a 6mm fasteners it is about 2.2 foot pounds, so basically useless. JB Weld isnt any better.

Marty's suggestion is the one I went with, ran a bottoming tap in all the way to the bottom, then threaded in a longer bolt, and voila........ May even be a permanent solution, we'll see. Thanks Marty and everyone!! I will install a KEEN SERT or similar next time the engine gets split. Now I am back to fiddling with carbs, getting fuel everywhere
 

iis_iis

Full member
Location
NSW
As Marty mentiones, in my Laverda case, using a bottom tap for the M6 holes for the primary cover retention, measure the actual depth and custom length match fasteners for each full thread depth. Using SS fasteners is a worry ( i use copper "grease" ) do this for all the smaller cross section fasteners in cast aluminum. Well done Martin, result for Paul L. j.
 

Dellortoman

Hero member
measure the actual depth and custom length match fasteners for each full thread depth.
Not a bad idea, but makes it a bit of a logistics exercise to get all the bolts back in their respective holes when you remove and re-fit the cover. You'd have to label each bolt or store them in a way that doesn't mix them up.

There's actually a good reason for leaving an air gap at the bottom of blind bolt holes, especially if you use anti-seize grease on the bolts. If enough grease ends up in the bottom of the bolt hole to cause hydraulic lock before the bolt is screwed in all the way, the bolt will stop in its tracks and further tightening can strip the thread or break the casting.

I discovered this to my cost while screwing down the cam cover on my Kawasaki Z1300. The bolts screw into lugs around the perimeter of the cylinder head casting. The threaded holes in the lugs are blind. One of the bolts started to get a bit more than finger tight before it was fully home. I figured it was nothing serious, maybe a bit of crap on the thread. So I flipped the Allen key around to use the long end for more leverage. The bolt went another half turn, then "Ping" the bottom half of the lug I was screwing into blew off the cylinder head casting. The threaded hole was still intact, but the blind end had blown out. The screw went in the rest of the way easily and pushed a blob of grease out of the now 'non-blind' hole. I presume the grease had accumulated over the years as the cover had been removed and replaced, with anti seize grease being applied to the bolt each time. The old grease already in the threads kept getting pushed to the bottom of the hole. It eventually got to the point where there was no more space in the hole for the grease.

A lesson here is to use anti-seize grease sparingly on a bolt going into a blind hole, and wipe any grease off the end of the bolt. Also, give the hole an occasional squirt of degreaser and blow it out with compressed air.
 

Tippie

Hero member
Location
Dr?bak, Norway
sorry Marty, I am going to need you to travel to Calgary to apply additional expertise.... another puddle of oil under the bike from the vertically split crankcases. I am going to try another bodge........ :eek: :eek:
A puddle while sitting on the bench? That is a serious leak. How far apart are the case screws? If you got it nipped up then it shouldn't be the screw at fault. Does it have a gasket, or relies on jointing paste alonep? I have seen threaded bar and a nut used for such temp repair, as it can be screwed as deep as possible.
 

Paul LeClair

Administrator
Staff member
A puddle while sitting on the bench? That is a serious leak. How far apart are the case screws? If you got it nipped up then it shouldn't be the screw at fault. Does it have a gasket, or relies on jointing paste alonep? I have seen threaded bar and a nut used for such temp repair, as it can be screwed as deep as possible.
uses a very thin brown paper gasket. I did not use any joint compound. Regretting that now, as it will be a truly major taks to split the cases to re seal.

now I guess the question in this thread is what external bodge I can apply to the outside of the vertical case seam underneath the engine - drain the oil, clean everything well, maybe even flip the bike upside down, and apply some sort of external sealer.....?? Suggestions?
 
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