MGB Engine rebuild, then...

[Rut]

I rebuild my 1970 MGB engine over the summer with a parts kit and advice from Hap and a machine shop owned by an MG enthusiast and friend. The reason for the rebuild was due to the engine sitting for years and the cam and lifter on valve #1 eating each other. The engine was bored .060 over, VP12 cam and short lifters/long pushrods, vernier cam gear and double row chain, 38cc Marina head with intake valve enlarged to 1.625", hardened seats and CR at 9.5:1. All the usual machine shop work performed and the engine ballanced, main and rod bearings .020, King bearings, etc...
I assembled the engine myself with Hap and the machine shop checking each and every stage, measured bearing clearance with Plastigauge, and everything checked and rechecked. Oil pressure on starter 50 psi + and once running 70 psi cold, 60 psi hot idle. Engine broken in with VR1 oil (high ZDDP) for 25 min at 2500 rpm and all readings normal throughout.
Once broken in and carbs/timing set the car idled at 1100 rpm and ran great, plenty of power and very responsive...everything I wanted. Im using the original rebuilt SU HS4s and they were set a little rich, but work really well.
Now, all that being said I developed a light rattle from the engine above 3500 rpm on a drive yesterday morning and stopped by the machine shop for a little help. The noise was diagnosed as a main bearing and the oil filter was pulled and cut apart to confirm. Oil smelled of gas and the SUs were cursed by the shop! Oil pressure is still at 60 psi and it was deemed ok to drive the 3 miles home to pull the engine, so I head home at 2000 rpm with no noise. I make it about 1 mile before the rod comes thru the block on number 1, the original lifter/cam failure site.
Once the car is home and up on jack stands I begin disassembly, drain the cooling system, etc. When I pull the carbs and intake manifold, both manifold throats are soaking wet with gas. I'll go over the carbs to correct that issue, but is that enough to cause an issue like this due to oil dilution?
Hap wants pictures at each stage of the tear down so he can help figure out what went wrong. Well, I got 90 miles of grins before this happened and I now have a winter (70 degrees today) project!
Rut

 

[drooartz]

YIKES!

No knowledge to add here, but I'm curious to see what you find out.

 

[pdplot]

Sounds familiar. Back in the '70s, I rebuiilt a TD and though the engine was in overall good condition, I had a valve job done (for $45.00!) and replaced all the rod bearings with the best available. I sold the car to a local guy and not two months later, he called to tell me a rod bearing had burned out. I commiserated with him but there was nothing I could (or would) do. I don't know how he might have abused the car and those TD engines are none too durable despite all the romanticism. I had a bearing run on my '51 TD back in 1955. Sounds like you did everything right. Again, let us know what happened when you tear it down. Hard to believe that leaking carbs or an overly rich mixture could cause that damage when your oil pressure showed so well.

 

[Gray_Cat]

It seems like if such a large amount of fuel was going through the carbs and manifold there would been a lot of black smoke through the exhaust. Back in the day I rebuilt several B engines with no failures like you describe and most were well thrashed by autocrossing. Having a rod through the block seems to indicate something more than a rich gas mixture. Please let us know what you find after tearing down the engine.

 

[Brinkerhoff]

If the oil wasn't diluted enough to cause the sump level to increase appreciably , then I would tend to think the block or crankshaft oil galleys weren't cleaned well enough. Just based on what you've given .

 

[Sarastro]

Well, until you get it apart, we're just guessing. However, I have a hard time thinking that some fuel in the oil would cause a catastrophic failure--early wearout of bearings, yes, but putting a freakin' ROD through the BLOCK? That's what happens when something breaks or otherwise comes apart.

Sorry to hear about the failure, though. I think you're remarkably matter-of-fact about it. I'd be drowning in beer and tears.

 

[Rut]

Gas in oil, confirmed...oil level at full mark, but should have dropped a little during break in. No smoke of any kind during the first and only 90 miles, ran like a scalded dog! My guess, either a bearing seized or a rod bolt let go, both up to me to check by torque or Plastigauge. Engine turned freely after each main bearing and rod bearing was installed and torqued, all caps marked once they were torqued. I'll know more once internal tear down begins and measurement taken...must say I'm hurt by this failure, thought I was better at this if it turns out to be something I did.

 

[Mickey Richaud]

I know it's a huge disappointment, but don't beat yourself up, Rut. It's a machine; they fail for all sorts of reasons. We've all been there.

Mickey

 

[PAUL161]

Rut, did you use new bolts in the rods with new nuts or the originals? A very common mistake done all the time. Reason I asked. PJ

 

[Rut]

Paul,
All new ARP fasteners torqued to ARP specs...I did reuse the main bearing studs and nuts, but checked with Hap before I did. Currently looking for an engine to rebuild and might as well add an OD tranny while I'm at it. This is my first B and I was on my way home from buying the tag for it when the first noise occurred...really like the way the car drives and handles.
Rut

 

[Brinkerhoff]

Yes Rut , hang in there ! My very first MGB engine rebuild experience ended in a disaster when I was sixteen. The good news is that MGB engines and parts are not rare. I have a core 70s MGB engine that is yours if you want. Its not like you holed ( and ruined) not one but TWO TD engine blocks like my friend Rick did !
Cheers mate!
Kevin

 

[Rut]

Kevin,
Thanks for the offer and I'll try to find one closer. We were VERY meticulous on this build and I'm wanting to pull the engine today, but SWMBO has other plans. I've removed everything but the block from the car and it's unbolted from the mounts and tranny, just waiting on me!
Rut

 

[DrEntropy]

We had the engine scatter in an MGB-GT on the Mass T'pike. We'd promised to sell it to a pal in Maine, this was the "delivery" trip, back in '73. I should write that experience up for an article: "How I Spent my Maine Vacation."

 

[Rut]

Dr,
That had to one heck of a trip! I pulled the engine today and dropped the pan to look at the carnage.
Rut

 

[Gray_Cat]

Wow, I ache for you Rut. When you get the engine completely apart you'll see better what happened. I'm thinking nothing you did caused the failure. You were so methodical with the assembly it leads me to think a part, oiling or metal component failure. Really gives me pause as the assembly of my 1275 nears.

 

[drooartz]

Wow. At least your engine is lighter now...

I too am really interested in what you find out. I'll be tackling my 1275 build one of these days (never built an engine before) and I've lots to learn.

 

[Brinkerhoff]

Does the crank journal look burnt? How about the insides of the bearings?

 

[Rut]

Well, the consensus between Hap and the machine shop is rod bolt failure. Michael, the machine shop owner told me about stress cracks in failed fasteners and what to look for...sure enough the bolt fit his description with a shiny area surrounded with a darker area. This picture does not show the end of the bolt, but it's the little $astard on the left! The rod bearing looked good as far as wear was concerned, so the oil dilution was not the cause. I thought I went ARP fasteners throughout, but reused the rod bolts...kicking myself a little harder after that discovery and it won't happen again!
Rut

 

[drooartz]

Well that sucks, Rut, but at least (very least) you know what happened. Good safety tip for the rest of us as well.

 

[Guest]

Three Oh Too!