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Post by alankelly on Feb 8, 2024 18:02:46 GMT 1
Hi All Just helping a mate rebuild his AC 250 engine Got cases back from vapour blasting and got this We think it’s water damage and thinking maybe fill with a smear of JB weld and neatly and carefully dressed back flat with a flat file, as want to avoid welding and re machining What does everyone think or leave and use yammabond on the base gaskets Just not happy leaving as is but feel if I get most of the damage dressed flat and then a small smear of sealant to prevent an air leak all is good and it then not just a bodge job (Going to leak test anyway once assembled) Thanks in advance Best wishes Al
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Post by midlifecrisisrd on Feb 8, 2024 19:05:29 GMT 1
Jeez that's bad, never seen it so widespread before
Looks like corrosion but maybe not helped by a porous cast
The godsend is that it's an air-cooled so separate heads meaning any slight discrepancy will be taken up and they can sit slightly different
Yes, fill the gaps with epoxy of some kind, jb weld is a good choice
I'd use genuine base gaskets so they are not just paper
I'd also use a smear of 3 bond to be safe
Steve
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Post by alankelly on Feb 8, 2024 19:10:21 GMT 1
Thanks Steve
Just spoke to Rob and think plan is to try and get studs out and then either fill with JB and then skim on the mill or a more drastic solution is maybe take off 1-2 mm and then add a spacer plate to replace the removed material
So next stage is try removing the studs and if that is successful can fill and skim or cut back
Best wishes Al
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Post by chrisg on Feb 8, 2024 19:37:55 GMT 1
Thanks Steve Just spoke to Rob and think plan is to try and get studs out and then either fill with JB and then skim on the mill or a more drastic solution is maybe take off 1-2 mm and then add a spacer plate to replace the removed material So next stage is try removing the studs and if that is successful can fill and skim or cut back Best wishes Al personally i would get it skimmed and use a spacer.
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Post by midlifecrisisrd on Feb 8, 2024 20:06:53 GMT 1
The studs would need to come out for either
Milling is the preferred solution if possible
Once the studs are out place a steel rule across and see just how bad it is
If the high points are the original face height epoxy would do as you are just filling the holes
If its eroded across a wide area or too much gone then milling is the only issue
Do you have a tool to remove the studs?
Steve
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Post by jon on Feb 8, 2024 20:47:12 GMT 1
Studs that have been in 40 years have a habit of being seized in my experience.
If it were mine I’d cut the studs down nearer the case and weld a nut with a chamfer on. The heat will help it remove.
Personally I’d drill out some 17mm hex bar and give it a good chamfer to get some extra torque.
I’d also get it machined and use spacers.
An air leak here could be disastrous.
Jon
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Post by alankelly on Feb 8, 2024 22:27:10 GMT 1
Hi all Ok studs out so at least that’s one less headache This is the results of the straight edge Worst area is between barrels But I think we could mill off 2mm and then add spacers? Any thoughts welcome Best wishes Al
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Post by alankelly on Feb 8, 2024 22:29:50 GMT 1
Next question please is can I source 2mm barrel base spacers “off the shelf”
Thanks for all the help so far
Best wishes Al
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Post by donkeychomp on Feb 8, 2024 22:41:19 GMT 1
If you get really stuck with this I have an RD250 engine sulking in the back of the garage.
Alex
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Post by alankelly on Feb 8, 2024 22:44:00 GMT 1
Hi Alex
That’s very kind but going to try a repair first
Love a challenge 😂
Best wishes Al
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Post by midlifecrisisrd on Feb 8, 2024 22:45:10 GMT 1
Are the gaskets not the same pattern as LC
Did Rob not get some made
Steve
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Post by midlifecrisisrd on Feb 8, 2024 22:48:52 GMT 1
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Post by JonW on Feb 8, 2024 23:31:57 GMT 1
Wow, Spacer is my thought as well.
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Post by shaunthe2nd on Feb 8, 2024 23:32:05 GMT 1
Hi All Just helping a mate rebuild his AC 250 engine Got cases back from vapour blasting and got this We think it’s water damage and thinking maybe fill with a smear of JB weld and neatly and carefully dressed back flat with a flat file, as want to avoid welding and re machining What does everyone think or leave and use yammabond on the base gaskets Just not happy leaving as is but feel if I get most of the damage dressed flat and then a small smear of sealant to prevent an air leak all is good and it then not just a bodge job (Going to leak test anyway once assembled) Thanks in advance Best wishes Al Ouch, that's bad Alan. How was it before blasting? do you think its the blast process that was the issue?
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Post by alankelly on Feb 9, 2024 9:36:03 GMT 1
Hi All Just helping a mate rebuild his AC 250 engine Got cases back from vapour blasting and got this We think it’s water damage and thinking maybe fill with a smear of JB weld and neatly and carefully dressed back flat with a flat file, as want to avoid welding and re machining What does everyone think or leave and use yammabond on the base gaskets Just not happy leaving as is but feel if I get most of the damage dressed flat and then a small smear of sealant to prevent an air leak all is good and it then not just a bodge job (Going to leak test anyway once assembled) Thanks in advance Best wishes Al Ouch, that's bad Alan. How was it before blasting? do you think its the blast process that was the issue? Hi Shaun No I am certain the damage was already present as could feel the base gasket face had some imperfections Trouble is the guy who had supposedly rebuilt the bottom end had just slapped a load of black paint on the complete bottom end including this gasket sealing area Now spoke to Rob and he is going to see if we can get a 2mm alloy spacer cut then I will machine 2mm off to removed the damage (and if any slight holes are left will feel with JB) then rebuild using the spacer to get barrels back to original heights
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Post by 4l04ever on Feb 9, 2024 10:46:30 GMT 1
2mm spacer ordered from laser cutting place :-)
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Post by Tobyjugs on Feb 10, 2024 11:38:44 GMT 1
I don't see any problems with using a spacer. It might come in handy as you can adjust the cylinders to the correct height depending on their condition and state of tune.
A very good sealant to use once you have the correct height etc. and are in the final build process is Loctite 5910. If i ever get a bad leak difficult to cure this is the stuff to use. Just one small problem with this stuff is it can be difficult to part the components when you need to strip them back down.
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Post by midlifecrisisrd on Feb 10, 2024 11:42:50 GMT 1
My first thought was to use a sealant like that and permanently bond the spacer on
Steve
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Post by Tobyjugs on Feb 10, 2024 12:13:51 GMT 1
Actually when i think about it we use and aluminum gasket material which is made up of lots of thin layers. You fit the component onto the engine measure the clearances then remove the component and peel the layers away until you have reached the correct tolerances. A bit too "over the top" for this sort of repair.
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Post by alankelly on Feb 10, 2024 14:21:25 GMT 1
If it machines and cleans up at 2mm, and I use a 2mm spacer, what’s the thoughts on case sealant between the case and the spacer and then the normal base gasket between the spacer and cylinder (of the correct thickness) to create the correct squish
That way I don’t need to allow for a “lower base gasket” as the case deck height will be as before?
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Post by midlifecrisisrd on Feb 10, 2024 14:34:27 GMT 1
As said that's what I'd do
Permanently bond the spacer on, single gasket, barrel on top Steve
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Post by 4l04ever on Feb 10, 2024 21:43:40 GMT 1
I would use 2 gaskets to allow for any distortion/tolerance to be taken up.
I run 2 base gaskets on my 4L0 with a 1mm spacer plate between them. Just fitted with a smear of grease to aid disassembly.
Leak down tested with no issues.
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Post by 4l04ever on Feb 10, 2024 21:48:13 GMT 1
Probably put a 0.4mm or 0.5mm on the bottom and a 0.25mm on the top. Should get close to OEM :-)
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Post by alankelly on Feb 12, 2024 18:20:32 GMT 1
All done and waiting for a 2mm spacer “Another one lives to fight another day” 😎
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Post by donkeychomp on Feb 12, 2024 22:10:19 GMT 1
Nicely done Al!
Alex
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Post by alankelly on Feb 12, 2024 22:12:01 GMT 1
Thanks Bloody hate doing stuff on other peoples bikes If you drop a clanger on your own engine thats just unlucky but you don’t want to do that on a friends😔
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Post by abar121 on Feb 13, 2024 11:11:17 GMT 1
Nice job Al!
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Post by steve63 on Feb 13, 2024 14:00:56 GMT 1
Excellent job Had it been under the sea for a decade? Just interested to know how this damage has come about. The outside of the cases look OK. It just looks like the gasket faces are corroded but everywhere else is fine?
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Post by lcmarky on Feb 13, 2024 15:57:07 GMT 1
All done and waiting for a 2mm spacer “Another one lives to fight another day” 😎 Good work & exactly what I would have done. You now have a good base to work with.
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Post by lcmarky on Feb 13, 2024 17:48:54 GMT 1
You could probably bore the damage out of the vertical pieces too and then screw some material back on in it's place..
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