Getting ready to begin engine work on my 70 coupe with L46, M21, 4:11 rear project. Background on this car. It was my Dad's car, last on the road in 1991 or so. From what Dad tells me he had the engine out and had it rebuilt in 91. He put the motor back in and only ran it for 500-1000 miles. Said it ran terrible, got frustrated and put it in the barn. 25 years later the motor is out and I'm trying to figure out what needs to be done at the machine shop. From what I can tell, the engine was bored .060 over and cast flat top pistons and new cam was installed. The block was not decked. After inspection it turns out the pistons had -.020 CH from original and the cam had 2 lobes already worn down. No wonder it ran like crap!! I have measured the bores and they are all at 4.063. It also looks like the mains were align bored and the crank polished. I am posting some pics for you pro's out there and looking for some opinions on what needs to be done to this block when I take it to the shop. I am thinking it just needs hot tanked and maybe light cylinder hone.

Let your opinions fly but keep in mind I am on a very tight budget.

 

No expert but this is what I see. The straight lines in the bore means fuel wash and the rings weren't rotating. Also looks like the ridge reamer may have been used too much.

You should state your goals so you can get advise towards it. I've ball honed and re-ringed a fresh build that was washed bad, but that isn't the best idea for a daily driver.

 

I think you should have left it together and put a new cam in it ! Looks nice to me. You could hone it, rings and brgs and reassemble.
Doing it on the cheap, Use set of 400 grit stone w/kerosene for cutting lube and LIGHTLY hone it. Crank looks good , you can hand polish it if you want. Again w/400 grit paper- wet. When you assemble have everything spotless clean. Most important. Dirt is death to an engine. I have an engine to build this winter also. Have fun -take your time- check everything twice. Plastigauge is o-k.

 

Guys, thanks for the input. Goal is to get the engine back together with minimal expense. Car will be driven a couple thousand miles a year tops. Planning on putting original dome or flat top forged pistons back in with 10-10.5 CR. Won't deck the block as its original to the car. Will use the original forged crank that's in the pics. Undecided on the rods.

There is no ridge at the top of the bore....just discolored. Never thought about that area being reamed too much. The pistons that were in it definitely had to go. With the deck being 9.025 and these pistons having a -.020 CH that would have put them .045 in the hole. Add another .040 for the head gasket and you get .085 quench....no good!!

Going back to original question. What do I need to do to get this short block back together? Can a guy who has never rebuilt an engine ball hone the cylinders correctly? Is that all that would be needed? What about cam bearings? With only 1000 miles on the motor, do they need to changed? I am not against taking it to a shop and having them clean it up and do some minor work for a few hundred bucks. Just want to know what I am getting in to if I go that route.

Is the bore size of 4.063 ok for a replacement +.060 piston? Looking at TRW .100 domes or possibly a forged Weisco flat top with a higher compression height to compensate for the 9.025 deck height.

 

Many people have gone to great lengths and expense to achieve maximum quench because it was assumed the quench played a big part in the engine's performance. Then along came the HEMI with no quench whatsoever and proved quench has no advantage at all. Yes, the quench does stir up the air/fuel just before combustion but the air/fuel is already stirred up just from being inducted on one side of the cylinder head thru an intake valve less than 1/2" open. Look at the average cylinder head used now days and you'll find most have little (if any) quench so it appears it was just an assumption all along.

 

Well I'm gonna shoot for .040 quench. CR had to be around 9:1 with those pistons....

 

Quench IS important. I would advise sticking with a flat top. Forged is nice but not necessary. 0 deck might be hard to achieve without decking it.

 

Yes from all I have read quench is important. Skip White has Weisco Pistons available. Here's what Skip has to say about them:

All of our Wiseco forged pistons are custom made for us and will sit flush in the block at a deck height of 9.015. If you have a virgin block then the deck height is at 9.025 and most machine shops will shave approx. 5-10 thousandths to remove any warpage and rough surface. This puts the block right at 9.015, creating a zero deck with these pistons. Most other catalog pistons sit .025 below stock deck height. Their reasoning for this is that should the block have been decked multiple times, then the pistons will not be sitting too far above the deck surface. It is rare that you will see a block end up at 9.000. And if you have one that is at that height then it would be highly compromised in our opinion. But should you decide to use a block with a deck height of around 9.000 then you can use a thicker head gasket to compensate for this.

 

I would have block shaved a tad , tank it , check it , cam bearings and all plugs replaced and get rotating assembly balanced .

 

I would have the block shaved i a heart beat but am concerned about loosing the VIN id on the block. It is a #'s matching car....

 

I'd re-measure the bores first. The clearance is built into the piston...so if they are actually .003 over 4.060...things are going to be awful loose. Best choice would be to let machine shop hone with torque plates to see if they will clean up and that bores are straight. Next choice is a flex hone which you can do at home...but it's a gamble if you aren't sure about the bores themselves.

You'll need to pull cam bearings and change. Not because of wear but because all that metal floating around in there from the cam lobes can easily get trapped behind a bearing and come out later. Need to clean block/crank REAL good.

Need to inspect lifter bores for size to find out why the lobes went flat. Verify lifters rotate as they should when cam is turned during assembly.

If your pistons end up .025" down in the hole, you can get .015" gaskets that work fine. No need to go out to .040" ones.

Piston to head clearance is a good thing to control. Even old Hemi's gain power when "quench style" pistons are installed. Search Dick Landy. My pistons are .028" from the head and do fine.

A good machinist can save the numbers on the block if they know what they are doing and are careful.

JIM

 

THAT was some good advice !!

 

Thanks 427!!! That's exactly what I had in mind. Guess I just needed some reinforcement from someone who has done this before. So my plan is this: Take to machine shop, clean/degrease, hone with torque plates, change cam bearings and check lifter bores. Shouldn't be too costly to have that done.

With regards to the piston to wall clearance, is there any advantage/disadvantage to using cast, hyper or forged? Do any have a looser tolerance or expand more when hot? I have also read that while the skirt clearance is recommended by the piston manufacturer, that you can get away with a little larger than recommended. Might be a little more noise but no harm to the engine....

 

Like someone said, the clearance is built into the piston. If the bores are in fact 4.063", they're .003" oversize to begin with, regardless of which type of piston you use.

 

Hypereutectics and cast run very tight clearances.....0005" to .002" max usually. Forged pistons made from 4032 material will run .002" or so...but I've run them out to .0045-.005" on my big bore stuff with no issues. I like to rev things a little! Forged pistons made from 2618 material are more hardcore and true race style. They might run .004-.008" or so. These are all generalities....the true measurements are based on bore size...it's a .000" per inch of bore thing. Bigger the bore...the larger the allowed clearances to a degree.

But again, the clearances are built into the piston. Piston skirt design allows differences in clearances also.

Need to measure your bores closely after they are honed and then decide on pistons. If they are already opened too much you may need a custom piston to save the block. Not a big deal...just costs a little more. And if you do that you can have them made to fit your deck height.

JIM

 

Thanks 427!! Good advice. I didn't realize you could custom order pistons. Was worried I would get the bores honed and then not be able to get pistons. Will look in to that. Wisco is local here in Cleveland.

Final question for you guys....Do I need to get the rotating assembly balanced after getting new pistons and possibly connecting rods?

 

Yes if the weights change much. If you're getting new pistons hopefully they will be a lot lighter and make up for heavier rods if you go that way.

If you're going for pistons and rods...you're not far off making a 388 or larger out of it.

JIM

 

I am concerned about the straight line marks in the cylinder bores, also. If there is any depth to those 'scratches, the block should be re-bored. If scratches are superficial, the bores should just be cross-hatched with a flex-hone tool to clean it up a bit.

Make sure all the oil passages are COMPLETELY cleaned out and that any block-off plugs are installed before you rebuild the block. I suspect that some kind of blockage in an oil passage may have caused the cam lobe wear, so be thorough about this work.

 

The scratches in the bores are superficial. I can't feel them with my fingernail...... The cam had 2 lobes that were down a bit. I can't tell if its the original cam or aftermarket. There is a good chance its an aftermarket came that was not broken in properly.

 

Looked into crate motors?