7R case weldable
 

Hi

I am honored to submit my first post to this forum.

As the title suggest I would like to know whether the 2.7 7R Mag case below is weldable. I don't know the history of the engine. A friend and I are in the process or rebuilding it. We received it in the state reflected on the photographs. http://forums.pelicanparts.com/uploa...1370093184.jpg

Welling case
 

I'm not a professional welder, but it doesn't look good to me. I'd try to search around for another used case, then have it checked and Casesavers installed.

it's junk.

That is a pity. Would there have been any hope in rescuing it had this been a aluminium case rather than a mag case?

I have heard varying opinions on welding to Die cast aluminum parts.

Most say you cannot because of porosity issues with the Die cast process but I have yet to have an authority comment.

Anyone?

You will need to be setup to tig weld magnesium specifically. A seasoned welder could probably reattach the missing chunk but you would then need to machine the spigot back true and inspect thoroughly to ensure bond. The repair would only be as good as the weld; check the metal surrounding the wound for spider fracture which could likely make the repair more complicated. If you have the resources it could be done but with unknown reliability relative to a new case half which is what I would recommend.

Tig Welding Techniques and Welding Magnesium - YouTube

Being a 7R case, which according to Wayne's book is stronger (and more desirable) than the older mag cases, I would like to give repairing a go. Off course I will be taking it to a specialist with a proven track record. I am currently searching for someone capable of doing this repair, but they seem to be few and far between.

Seeing that the break is to the top of the engine I was hoping that it may be more repairable, as opposed to had the break been at the bottom of the case.

I would hate to go through the rebuild exercise only to discover the case leaking!:mad:

No way Jose!
Just get another case.

A 2.4 liter 7R would be a little stronger than the others, but a 2.7 case is mostly crap.
I have a friend who search forever for a good 2.7 case, but every case (10+) he looked at was cracked.

replacement case
 

i would go with a replacement case, post wtb on here you will find them to be reasonable.

What JW said. He knows his 5hit.

No good reason to even try to repair it.
Find a replacement. You will also need a new crank.

http://forums.pelicanparts.com/uploa...1370472809.jpg

http://forums.pelicanparts.com/uploa...1370472820.jpg

Well, I had an exhaust valve head fall off into this #3 cylinder, which led to the rod bashing the 7R 2.7 case a bit worse than this, though only the top side was busted as I recall. A shop took the case to a suitable welder for me and they welded it up (forget about using the broken off bits, which you probably don't have anyway), and machined it. At my request, they line bored it.

I may have made two mistakes. I did not specify that the welding be done with the halves bolted together. Maybe they did, and in any case nothing indicated that the case was warped.

And I did not require that the #8 nose bearing bore be left alone. So I was stuck with a super expensive oversized bearing for that one. The others were expensive enough oversized. I didn't know of the clever technique of shaving the mating surfaces and line boring back to stock, and it wasn't in common use 20+ years ago. This shaving should also deal with minor welding warpage, if any there would be.

Eventually I used the case for a 2.7 liter race motor - S cams, twin plug, ported some, Weber 46s, 9 something to one CR. Ran great, but its life was greatly shortened by failure of a wrist pin circlip, whose end with a hole broke off (rest held the pin in just fine) on non-slipper skirt pistons, so it couldn't fall harmlessly into the sump, and instead etched the cylinder and shot a lot of sharp bits through everything. And a problem with the TimeCerts of my own making, and when these start pulling, I don't think there is much else which can be done.

Anyway, contrary to the opinions of some very experienced guys, I'd say you could. Talk with Ollies. I know for a fact that the older sand cast aluminum cases can very successfully be welded. Ollies, at least before moving to AZ, had a stock of busted cases they could cut slices out of for repairs. And this magnesium alloy is certainly weldable and machinable. Takes the right equipment and knowledge, and you can't do it with your home MIG and sandpaper. But it can be done. When I had it done, it cost effective - used 2.7s with not too great leakdowns were running maybe $3,000 as donor motors. I don't recall what the welding and machining cost, but pretty sure more like $500 - back then.

I reused the crank. It was straight, rang true, and I think I raced it for 15 years. Good idea to check it, though. If your damage was from rod bearing failure, rather than a valve breaking, that might be a different story.

Now if Henry's picture is meant to imply that he has good condition 7R cases all cleaned up and specs checked sitting there waiting to find a buyer, for sure you should check that out. Save a lot of headaches and hunting around.

The picture is meant to imply that we certainly have cases that can be inspected to determine usability and the product would without doubt be cheaper and considerable nicer than a welded and properly machined mag case.


BTW: The combination of case damage and missing rod would indicate crank damage due to rod failure. Damage to the #3 rod quite often means oil pump damage as well. IMHO

There's a 7R on Ebay right now from a 73 2.4T. They are asking $995. Just thought I'd mention it.

7r case for sale
 

I have a 74 case for sale $800.00 . PM me if your nterested.
Jeff

May I use this existing thread to ask for advise regarding my 77 RoW 7R that I have just aquires in Germany: after stripping down the CIS I found the right case to having been welded between two cylinders at some point. Neither proximate head stud nor case bolt seem to have been the problem.

As probably most I intended to build an RS replica performance motor, carbs.. The usual.

Frankly, previous postings worry me quite abit. Could somebody please advise on what best to do?

Thank you very much,

Regards, Jan

There might be a reason, like matching numbers maybe??;)

I'm afraid this is correct. Thats a critical area and welding (and machining) will not restore the strength & rigidity needed here.

Time to shop for a replacement, however this is also an opportunity to perform the forensics to find out WHY it failed. That prevents an "encore performance".

My $.02
Anything can be rebuilt....anything!!
Should you...well..that depends on many factors.
If this were the winning engine from LeMans...probably.
If it were the only engine to ever have made over 1000HP on pump gas while spinning at 20K RPM...maybe.
Other than that...yes you can spend 30K on repairing it...or make a coffee table out of it...and get another case.
Bob

Inside and out gone .half case broken rod broken probably crankshaft and oïl pump and cylinder head .Buy another one a lot cheppier.

Here is what I am referring to:
http://i1282.photobucket.com/albums/...ps4ebc5894.jpg
http://i1282.photobucket.com/albums/...psa55cd820.jpg

Thanks, Jan

Opposite of the rod for the other side... curious what the inside looks like.

I "solved" the problem by returning the engine to the seller and collected my money. Thank god this worked out so smoothly.

Thanks a lot, everyone. :)

#2 rod my thought also. However, when things have gone sour on my motors, the rod did its damage on the same side as the piston, cylinder, and head area it inhabited. Such as sawing a slot in the case up to the crankcase breather area. externally the opposite case half was not damaged (interior damage basically cosmetic on that side).

Perhaps if a rod bolt failed, the crank could kick the big end up hard enough to bust out a chunk in the area shown? Sometimes a case sort of lucks out (some) after a failure, with the detached rod big end lodged somewhere so it stops flailing around.

@ Lapkritis & Walt: I share your opinion, thanks for pointing this out to me - it opened my eyes on cause and possible effects of this damage. On the upside, we saw that cylinders must have been renewed more or less recently due to no visible corrosion. On the downside, I realized that one CIS cylinder heads had a 1973 date stamp on it, with the inlet port looking a bit smaller in diameter at first glance.

Since the motor must have had an interesting life, I simply lost confidence in this buy in the end. Happy that this lesson was rather inexpensive, all in all...

Different port sizes would be quite a negative sign!