Scored Main Cap Bearing - Ouch
- Thread starter blewbyoutobad
- Start date
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Yes it will be when it is rebuilt. I am not going to try and repair it in the car, so once it comes out it will get a good cleaning and some machine work, then a good cleaning etc. I am going to invest money in heads and a cam and leave the stroker alone for now. Thanks all you have given really good advice and ideas. I will be building the next one myself.
Wyrmrider
Well-Known Member
and ixnay on scotchbright and wd-40
wd-40 embeds grit into pores instead of floating it up and out
wd-40 embeds grit into pores instead of floating it up and out
Marcohotrod
Well-Known Member
I do not see how the flywheel bolts and flywheel were not too long on a previous crank and block? washers before and not this time. I think all factory bolts and crank flange thickness and flywheels are the same. I have manual 340s since 1978, never needed to drill from cam feed to thrusts. I do use a 3/4 groove #3 bearing
I talked to him on the phone and he wasn’t sure if there were washers or Star washers under the head before. Hey strange stuff happens to all of us. At least he isn’t afraid to get his hands dirty and figured it out.
nm9stheham
Well-Known Member
You made me look, MH ..... Why are there two wear patterns on the back of the #5 main cap in the 2nd pix in post #30? Aren't the flywheel bolts at the same radial distance around the crank axis? So is the edge of the flywheel's mounting recess contacting the back of the rear cap? If so, why?
I also just checked the rear surface of the #5 main cap on an early 360 and a'68 273 block, and neither has the inner step on the back of the cap behind the rear seal area, as seen in that same pix......???? It is almost like the rear flange of the crank has been shortened or the rear cap is not matched to the block.
Marcohotrod
Well-Known Member
the flywheel bolts on a small block mopar and every other engine I have seen are at the same radius from crank centerline. I think too long bolts and or no washers machine the rear of the cap and block. I think factory flywheel bolts used star washers. I use grade 8 flat washers
There is only one groove. The other one that looks like a groove is not. It is the same height as the rest of the bearing cap.
nm9stheham
Well-Known Member
OK, now I see. I was confusing the light and dark areas, thinking that sharp edge/groove was a step. Tnx
yellow rose
Overnight Sensation
Did you ever determine if the chamfer on the oil holes was what was scoring the bearings?
It appears that either they did not chamfer enough but if feels like there is barely any at all. Almost all the wear area is directly associated with the oil hole.
I also found #8 rod bearing totally wiped out, but #7 looks fine. Weird
yellow rose
Overnight Sensation
I'm sure that's some of it, but the big scoring looked like not enough chamfer on the oil holes.
I always chamfer the main and rod feed holes before grinding. And add extra chamfer because some of it gets ground away.
I will chamfer them if the crank is ground already, but I don't like doing it any more if I can avoid it. My hand isn't as steady as it once was.
yellow rose
Overnight Sensation
I'd depends. If it's going out to be ground I use a...well...now I have to go out and look but IIRC its a 1/2 double cut round burr, and then it hit the finished chamfer 60 and then 120 grit paper rolls and send it to the grinder.
If the crank is done, I have some 1/2 round stones (aluminum oxide IIRC) that I use and stone them.
The stones can take double the time but as you know, you have much less chance of scratching the crank because they aren't so grabby.
Edit: I have 3.79 crank out there for my W2 junker I'm going to do. I was going to turn the rod throws to 2.100 and use a 6.250 Chevy rod so I can use an off the shelf piston for a 4 inch stroke with a 6.123 rod, but I scratched that idea because everything I'm finding in off the shelf Pistons has 1/16 1/16 3/16 ring packs and I want .043 .043 1/8 so I'm just going to use it and it needs the oil holes chamfered.
nm9stheham
Well-Known Member
Not weird at all, #8 rod bearing is fed from the #5 main; #7 is fed from the #4 main.
Possibly some crud/crap/debris left in the oiling path to #5, which, has been pointed out, is a partially separate oiling path vs. the path to 1-4. Would the 'scrapings' off of the #5 main bearing from a sharp edge on the oil hole wipe out the #8 rod bearing? IDK
I need to study the oil flow path once all the bearings are out to see if I can any sense of this. I think a poorly ground oil chamfer on the rear main started the problem along with the too long of bolts on the flywheel.
So let me ask a really crazy question. If the only journal that needs some polishing is the rear main can I go ahead and just replace all the bearings, clean up the rear journal and grind off the flywheel bolts. This mtr is on its second oil change and I am wondering if all this happen 4-500 miles ago. Of course some has probably happen since but I'm think that most of it happen on initial startup and break in. I am going to pull the oil filter and cut the top and look at the element. What do you all think about this? I would also check the oil holes in crank for chamfer and cleanliness.
So back in the day I had a similar situation, fixed the crank replaced the bearings all was good until! One lifter collapsed, no biggie changed out the lifter and another one collapsed, pulled the lifters apart and they were full of metallic sparkles. That meant the rest of the engine was too.
Marcohotrod
Well-Known Member
polish rear main and #8 rod journal and measure diameters- may be small. front thrust surface on crank may be worn down.
Yes that is my worry. I do have solid cam so is there a way I can flush the engine. I know I am taking a risk for me a 66 year old man, tearing all this apart is a nightmare. I dont have my lift anymore.
I will pull pump down and inspect if other journals are not damaged.
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