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Repairing Damaged crankcase thread.

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Engine Doctor24/05/2020 12:13:59
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 I thought I would share this repair with you as I see loads of otherwise good engines being sold as scrap or bodged with glue . This is a repair that will last and is as strong as the original casing .

I recently bought a McKay 30cc petrol engine that had a damaged exhaust mounting thread on the crank case . These are excellent engines and after recently selling one and regretting it shortly after I thought this is an opportunity worth taking a chance on .

The first pic is of the damaged mounting . This was drilled out and the cracks around the mounting have been ground out to clean and allow them to be filled 124_2419.jpg

The crank case was completely stripped apart from the small nipple , as this would be fine during the repair process , and was then thoroughly de-greased

Edited By Engine Doctor on 24/05/2020 12:15:55

Engine Doctor24/05/2020 12:26:55
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2512 forum posts
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The next stage was to make a sort of oven with some fire bricks to keep the heat in. As Ali conducts heat so well even a small breeze can cool the case enough to stop the repair (Welding/Brazing ) working 124_2422.jpg

Dont take any notice of the Techno Weld packet in the pic . Techno weld has a higher melting point than the rods I used and past experience has shown that it can cause crankcase moldings to blister or deform . The rods I'm using melt at 300-350 deg C . A normal blowlamp is being whit a propane /butane mix . A lot of heat is needed and the whole case will need to heated to the melting point of the rods .

The case is heated and the rods rubbed onto the area that needs repairing . when the temp is correct the rods will start to melt. Be careful to keep the rods away from the flame or they will crumble . Melt some alloy into the repair and then stir with the stainless steel rod to break up any oxides that may get trapped . then fill the repair completely . It will shrink down slight ly as it cools so if possible try to overfill slightly .

Edited By Engine Doctor on 24/05/2020 12:27:31

Engine Doctor24/05/2020 12:30:26
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2512 forum posts
39 photos

124_2421.jpg

Here the case has been filled and both ends repaired and allowed to cool naturally . Dont cool with water as this can cause distortion to the case and cracks to form in the repair alloy.

Engine Doctor24/05/2020 12:33:03
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2512 forum posts
39 photos

Here the repair has been ground to shape with a Dremmel prior to being drilled and tapped and final finishing .

124_2423.jpg

Barrie Lever24/05/2020 12:37:18
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243 forum posts
50 photos

Doctor

Good advice there, what brand of rods are you using?

Interesting the way that the case is scratched through the puddle of molten material, that is a similar technique that can be used to solder aluminium.

I might write it up later today.

B.

J D 824/05/2020 12:41:41
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1496 forum posts
84 photos

That looks like a great repair. Barry beat me to it, what rods were used ?

Engine Doctor24/05/2020 12:45:25
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2512 forum posts
39 photos

The case was then drilled and tapped to the correct thread and finally bead blasted to give it an almost as new look .124_2429.jpg

124_2430.jpg

Cas looks as new now although the casting marks on the fins does let it down a little .

A very satisfying repair but was marred a little by my clumsy fingers breaking the piston ring while reassembling the engine !Duh. A new ring only cost £12 ish from a very talented chap on e-bay .

I have also just repaired a SC 61 crankcase with similar damage . I was a little worried while repairing the SC as in the past the cases have blistered but these rods with a lower melting point certainly seem to do the job .

Next repair , sometime in the future, will be an attempt to repair the exhaust mounting one OS 52FS cylinder head

Doc Marten24/05/2020 12:47:41
583 forum posts
8 photos

I'm loving this!

I have some techno rods and Alu build 300, what should I use where?

How did you space the new hole correctly?

Ah, Mr Gaviscool is a very useful trader to save on ebay.

This is a great introduction for a Winchy type thread, fancy it?

Edited By Doc Marten on 24/05/2020 12:53:29

Engine Doctor24/05/2020 12:49:11
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2512 forum posts
39 photos

Hi Barrie , JD8 . I'll check the brand , if there is any on them and get back to you . I found them on E-bay under "Low temp aluminium rods " and the firm selling them was in Chatham . As said I'll look it up and post it or PM the details .

E.D.

Engine Doctor24/05/2020 12:53:44
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2512 forum posts
39 photos
Posted by Doc Marten on 24/05/2020 12:47:41:

I'm loving this!

I have some techno rods and Alu build 300, what should I use where?

Ah, Mr Gaviscool is a very useful trader to save on ebay.

This is a great introduction for a Winchy type thread, fancy it?

Edited By Doc Marten on 24/05/2020 12:49:45

The Techno rods I have melt at about 600c and is a bit dodgy on pot metal of the metal used in pressure diecasting.

I would use the Alu Build 300 as the name suggest that they melt at around the 300 + deg mark.

Engine Doctor24/05/2020 13:00:08
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2512 forum posts
39 photos
Posted by Doc Marten on 24/05/2020 12:47:41:

ere?

How did you space the new hole correctly?

Ah, Mr Gaviscool is a very useful trader to save on ebay.

I had a Exhaust extension to measure and mark the hole for drilling .

Other than that if you know the distance between centers its not difficult to mark out if one of the holes is intact.

On Engines that have a through bolt,I block the hole below the damaged area with an old bolt and build up the damaged area . Then use the undamaged part of the hole as a guide for drilling out the welded area .

Doc Marten24/05/2020 14:35:17
583 forum posts
8 photos
Posted by Engine Doctor on 24/05/2020 13:00:08:
Posted by Doc Marten on 24/05/2020 12:47:41:

ere?

How did you space the new hole correctly?

Ah, Mr Gaviscool is a very useful trader to save on ebay.

I had a Exhaust extension to measure and mark the hole for drilling .

Other than that if you know the distance between centers its not difficult to mark out if one of the holes is intact.

On Engines that have a through bolt,I block the hole below the damaged area with an old bolt and build up the damaged area . Then use the undamaged part of the hole as a guide for drilling out the welded area .

Cool.

I go edge to edge for centres but others may not know or use another method?

ken anderson.24/05/2020 14:38:50
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8686 forum posts
808 photos

well done ED ,I'm impressed...

ken anderson...ne...1..impressed dept.

Barrie Lever24/05/2020 15:57:59
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243 forum posts
50 photos

ED

That is tidy work.

I have checked on Ebay but I am not 100% I have found the right rods, the most likely looks like Durafix with 388 Deg C melting point.

Regards

B.

Engine Doctor24/05/2020 16:16:40
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2512 forum posts
39 photos

The rods I used are Alu Build 300 . They are sold as Aluminium Brazing/solder rods sold by ablemablecrafts.

hope this helps

Barrie Lever24/05/2020 18:26:51
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243 forum posts
50 photos

ED

Thanks two rods purchased, got to be worth having in the workshop for the emergency job.

Thanks

Barrie

Engine Doctor25/05/2020 11:06:03
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2512 forum posts
39 photos

Hi Barrie , as you say " well worth having for emergency" . I once made a incowl silencer using Techno weld and Ali sheet . Worked ok but difficult to get to flow into tight joints. This lower temp variety may make those sort of jobs easier. I haven't yet tried the rods containing flux or the liquid flux .

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