Stripped thread in heat exchanger...ideas?

Iain C

Iain C

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Engine is a Lombardini M602, and whilst re-assembling after having flushed the tubes out, I noticed that one of the allen bolts holding the end caps that hold the tube nest in the heat exchanger had stripped. It came OUT with the "other" thread on. Really annoying...it was the first time I had done that job so obviously someone had got over-zealous assembling it in the past!

I'm really trying to avoid buying a new heat exchanger/exhaust manifold so if I can repair it, that would be good. It looks like an M5 or M6 allen bolt (not checked precisely), thread length about 20mm, going into a female bolt hole in cast aluminium. It's one of 3 bolts holding the end cap on (12, 4 and 8 o clock positions approx respectively).

I was thinking of the following:

-Re-assemble with chemical metal and a new bolt
-Fill with chemical metal, drill & tap, and new bolt (concerned about accuracy, and tapping into such a short blind hole
-Chemical metal a stud into it, and use a nut on the outside
-Helicoil
-Or worst case scenario lots of blue gasket sealer and crossed fingers!

Anyone have any better ideas or experiences with these? And if it's a helicoil, where on earth am I likely to be able to get some between christmas and new year (either around Rugby, Midlands, or Gosport, S.Coast)

Looking like new year on the Isle of Wight might not happen now...:(
 
Thans but no chance. It must be a nut/bolt type of mechanical arrangement in the original hole.
 
'Fraid the Helicoil is the most reliable and strongest repair. In fact it will be stronger than the original - by far! Not familiar with the specifics of the Lombardini design. It wouldn't be possible to drill the lost hole through and its counterpart and put a length of studding the whole length of the assembly, i.e. from one cap to the other?

Rob.
 
Iain C said:
Thans but no chance. It must be a nut/bolt type of mechanical arrangement in the original hole.
Click to expand...

Hi, sorry to hear of your heat exchanger problem. I have had 45 years of fixing motor bikes for impecunious owners. Many of these had stripped threads. If you can access the stripped hole with a drill,or even a tap, you can increase the size of the hole and use a bigger screw.5 will go to 6,6 will go to 7.7mm screws are not easy to find-lambretta scooters use them. Otherwise you need a thread repair kit like a helicoil kit.If access is difficult the part will need removing so the job can be done on the bench.Hope this helps,Rotrax.
 
If you can get a Helicoil in it cant you drill and tap slightly bigger.If its metric you could possibly get a different thread type, ie Whitworth.They have quite a coarse thread and would be good for Ally.You can still get the taps from a good tool shop,or internet.
 
As a temporary fix, drill out to helicoil size and fill with epoxy. Drill and tap out to original size and fit. When you have chance drill out the epoxy and fit a helicoil
 
That's great guys, thanks for the response. Looks like Helicoil is favourite then...hope I can find somewhere open between now and new year! What I was really dreading was "nah, that's goosed, get yourself a new heat exchanger!"

Next question, is it possible to re-use the gaskets between the exhaust ports and the heat exchanger? Not ideal I know, but if that's what it takes for new year on the IOW then I'll give it a go! Of course, if Golden Arrow Marine or another Lombardini stockist are open tomoroow then hopefully the problem evaporates anyway...
 
Hi I feel Rotrax has the basic answer for a cheap long term fix, because if you have stripped out the thread of a 5mm thread, then this is likely to leave about 5 mm diameter hole, and this is the tapping size for a 6mm machine screw, so just run a 6 mm ISO course tap down the hole and screw in a 6 mm allan socket machine screw, although you will probably have to enlarge the cap hole as well.( If it is a 6mm thread and you need to go to 7mm bolt forget it, and go the helicoil route). However I feel the crux of the post is that you want to go sailing NOW and most places will be closed till January. So for a temp fix I would chemical metal a steel stud in place, and put on a nut with plenty of gasket sealant to take up the gap,and gently tighten. The remains of the thread profile in the hole and the stud should give a good mechanical bond and the chemical metal should hold up to the shear forces for the few days you are out. As for the gaskets if they are substantually intact, use an exhaust cement from a car shop, if they are not exposed to high temp then blue hylomar is my gasket cement of choice.
Good luck and I hope you manage to get sailing
 
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neil_s said:
Helicoils are very good and quite easy to do. The important bit is using the correct size of drill bit before tapping. You can get kits from these people.

www.namrick.co.uk

Cheers! Neil
Click to expand...
Hang on a minute, though. Is a stainless helicoil insert in an ally casting working in seawater not going to brew up nasties later on? S/S + ally + hot seawater sounds a recipe for tears next time it needs dismantling?

Maybe it does work OK, but I would just check with the makers first?

Personally I would go for threading for the next size bolt, if there is enough thickness in the casting to do it.
 
Sandeel you've hit the nail on the head, I did ideally want to get away for new year.

If the collective agrees that chemical metaling a stud in place should hold I think that might be my preferred route.

The exhaust gaskets are perfectly intact (they are metal) but obviously a bit squished as they have a "profile" which I assume squishes down the first time they are done up. Is blue Hylomar a suitable "exhaust gasket" to make up for any imperfections? I guess as it needs to be the block to heat exchanger gasket, it will be needing to deal with some fairly high temperatures?

All the marine Lombardini dealers would appear to be closed, however I have spoken to some industrial generator people who have been very helpful...although the part numbers are all totally different you never know!
 
Iain C said:
The exhaust gaskets are perfectly intact (they are metal) but obviously a bit squished as they have a "profile" which I assume squishes down the first time they are done up. Is blue Hylomar a suitable "exhaust gasket" to make up for any imperfections? I guess as it needs to be the block to heat exchanger gasket, it will be needing to deal with some fairly high temperatures?
Click to expand...

I re-used the exhaust/ heat exchanger gaskets on my Beta B622. No problem.
I wouldn't use gasket compound if the gasket looks OK.
 
act in haste .....

repent at leisure . Which ever way you to fix, you should be sure that the repair is man enough , and seaman like enough to be safe to put to sea , bearing in mind current low temperatures , your life might depend on it .
 
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