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Looking for advice on slant rebuild...
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Author:  briwill [ Tue Jun 02, 2020 9:22 am ]
Post subject:  Looking for advice on slant rebuild...
I have 65 Dart that I picked up a few months ago. Was sitting for 20+ years with a bad transmission. I rebuilt the trans, brakes, suspension and got it running a month ago. Was running good but lacked power. I did a compression test and all cylinders were between 140-150psi. Adjusted the valves and the head was very clean inside. This led me to believe the engine had been rebuilt at one time. I decided to pull the engine last week to fix a dent in the oil pan and a broken exhaust stud. Once I removed the engine it was apparent that only the head was rebuilt or replaced at some point. The most disturbing discovery was a thick, nasty sludge in the bottom of the oil pan. This is after 2 oil changes and about 30 miles of driving. Makes me sick to think this was pumping through my engine.
My question: Should I pull all the main/rod bearing to check for wear? Plastigage them? Since the compression was good I hate to pull the head. My plan is to clean it up, get my cam reground, add super six intake/weber and HEI ignition. Advice?

I already spoke to Oregon Cam and planning to go with the 2106 grind. I have a Super six intake and 32/36 Weber ready to go and electronic distributor, HEI coil and GM style ignitor. Planning to keep stock exhaust manifold and already have a new 2.25 exhaust. Thinking this combo should wake up the slant nicely.
Author:  Joshie225 [ Tue Jun 02, 2020 12:18 pm ]
Post subject:  Re: Looking for advice on slant rebuild...
It seems unlikely you would find anything pleasant if you inspect the main and rod bearings. If I were to put in new bearings I'd want to pull the crank and at least have it polished assuming it isn't too worn or out-of round on any pins. Removing the crank requires removing the pistons and rods so there goes leaving the head in place. If the crank looks quite nice though you can roll in new bearings.

The Oregon 2106 looks good, but I think you want 2106R with more intake duration than exhaust. If you are wanting to improve the engine performance to the point of changing the cam then you're back to pulling the head so that you can check and increase the compression ratio to best suit the cam. You'll be most of the way there anyway with having removed the manifolds to swap them and the valve gear to change the cam. You're losing power and economy if you don't get the compression up where it belongs.

Welcome aboard, BTW. :D
Author:  Dart270 [ Wed Jun 03, 2020 3:49 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Too bad you didn't measure the oil pressure before you pulled it. That would have told us something about the condition of the bearings and crank.

It really depends on your budget and time and needs/wants. If it was running OK, and the oil light was not on at idle, then maybe you'll be OK with cleaning the pan and pickup and putting the motor back in. This is a dice roll, but if you want simplicity and can afford to pull the engine again if it doesn't work, then it would be worth a try. Sometimes it's better to leave something alone if it was working rather than try to fix part of it and do further damage. 140+ psi cranking is quite good, indicating the pistons/rings and associated schtuff are in working shape. My guess is once you pull the crank you will end up doing a full disassembly and rebuild in order to get everything clean, and that gives chances for goofs...

Lou
Author:  briwill [ Wed Jun 03, 2020 9:16 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Wish I had measured the oil pressure before pulling but didn't have a gauge attached. I've built a couple dozen engines over the years so not worried about pulling it completely apart. I've just already spent way too much money on the project and want to be driving it in a few weeks. I will measure a couple bearings and go from there. I pulled the cam yesterday and it looked ok. No wiped out lobes but the cam bearings seemed to have a lot of slop. If I flip the cam around and put the first bearing surface in the block, I can move it around a bit. Is this normal? What is the best way to measure this?
Author:  DadTruck [ Wed Jun 03, 2020 9:36 am ]
Post subject:  Re: Looking for advice on slant rebuild...
the slant motor that I ran in the 68 Barracuda drag race series is basically the stock 50 year old,,xxxxxx mile motor.

took the motor completely down, kept track of what pistons - rings - bearings were where,,,
Had the block - head hot tanked to remove the sludge,
Installed new: cam bearings, freeze plugs, timing chain, valve seals, valve springs and an oil pump from a hydraulic lifter slant motor.
milled the head to get the compression up to the high 8's, had a mild re grind put on the OE cam.

The cylinder bores had a ridge that you could catch a finger nail on at the top, did not do anything to that. The bores were out of spec for size, taper, roundness.
I ran a ball brush thorough the bores to re establish the cross hatch and that was it, then re assembled the motor with the OE pistons, rings, main and rod bearings
valves, pushrods, rod bolts, head bolts.....

I do run 15w 40 diesel motor oil, oil pressure is good with the motor hot or cold.
Also added MPFI, Hooker Long Tube headers, MSD ignition, the motor should be around 160 HP.
It has survived 50 + trips down the strip, normally shift at 5500 RPM. Never a wimper, a knock or a miss out of that motor.
It just runs,,,There is no blue smoke at start up or while on the throttle.

There is nothing wrong with rebuilding them 100% back to factory specs or better,, but depending upon what you want to do with the vehicle, that is not always necessary.
Quote:
I can move it around a bit
I would go with new cam bearings,, pretty cheap and can have a big impact on oil pressure, also if you take the block completely down to get it hot tanked the cam bearing will get knocked out anyway.
Author:  Dart270 [ Wed Jun 03, 2020 9:48 am ]
Post subject:  Re: Looking for advice on slant rebuild...
The cam bearings have different diameters, larger in front of the block and smaller toward the back. There will be a ton of slop if you have the rear cam journal in the front bearing. I bet it's fine.

OK, oops, I see you flipped it around. A little slop is fine and if no scoring on the bearings then you should be OK.

Sounds good to measure a couple of bearings and go from there.

Lou
Author:  Joshie225 [ Wed Jun 03, 2020 9:49 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Quote:
Wish I had measured the oil pressure before pulling but didn't have a gauge attached. I've built a couple dozen engines over the years so not worried about pulling it completely apart. I've just already spent way too much money on the project and want to be driving it in a few weeks. I will measure a couple bearings and go from there. I pulled the cam yesterday and it looked ok. No wiped out lobes but the cam bearings seemed to have a lot of slop. If I flip the cam around and put the first bearing surface in the block, I can move it around a bit. Is this normal? What is the best way to measure this?
That kind of cam bearing wear is unusual. Cam bearings are cheap, but the tool is not. As you have experience with full rebuilds I would take the motor apart completely and have it hot tanked to get all the junk out and new cam bearings installed. Yes, it puts off driving the car, but it will never be any easier.
Author:  briwill [ Thu Jun 04, 2020 7:06 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Well, here I go down the rabbit hole. Pulled the engine completely apart last night. I took another look at the cam bearings and they appear to be ok. I guess I was fitting the back of the cam in the front bearing. Crank looks good but main and rod bearings have some streaking from what looks like oil starvation. Will plan to polish crank and get fresh bearings. Hoping to re-use the pistons and rods with fresh rings. My biggest concern is the ridge at the top of the cylinders. They all came out ok but one of the ridges feels pretty bad. Wish I had just left them in since I had good compression. Cylinders look good with no scoring on the walls. Is the ridge a real concern?
Author:  Joshie225 [ Thu Jun 04, 2020 8:12 am ]
Post subject:  Re: Looking for advice on slant rebuild...
If you're going to hot tank the block the cam bearings still need to come out. The usual cam bearing failure mode is to lose pieces of the bearing surface rather than to wear heavily.

The ridge isn't great, but it's not catastrophic either. The ridge means that the cylinder(s) are almost certainly out of spec for taper. The engine is likely to run fine, but will use a bit of oil and maybe lose some power due to ring flutter. The question I would ask is: How long and how far you want to use this engine before it gets pulled apart again? If it's less than 50k miles I'd clean everything really well and only replace parts that fail inspection.
Author:  briwill [ Thu Jun 04, 2020 8:42 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Quote:
If you're going to hot tank the block the cam bearings still need to come out. The usual cam bearing failure mode is to lose pieces of the bearing surface rather than to wear heavily.

The ridge isn't great, but it's not catastrophic either. The ridge means that the cylinder(s) are almost certainly out of spec for taper. The engine is likely to run fine, but will use a bit of oil and maybe lose some power due to ring flutter. The question I would ask is: How long and how far you want to use this engine before it gets pulled apart again? If it's less than 50k miles I'd clean everything really well and only replace parts that fail inspection.
I doubt I would ever put more than 10k miles on this engine before I pulled it for something else. That said, I hate to put together something that is going to have issues.

Looks like you are local. Do you have a machine shop you recommend in the Portland/Vancouver area?
Author:  SpaceFrank [ Thu Jun 04, 2020 11:18 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Quote:
Removing the crank requires removing the pistons and rods so there goes leaving the head in place. If the crank looks quite nice though you can roll in new bearings.
Not relevant now, but... I replaced a set of rod bearings without pulling the crank when I was in a hurry to get ready for a race. The head was off at the time, but I just slid the pistons all the way up the bores until they rested on the cylinder ridge; I didn't want to risk breaking the rings getting them out. It wouldn't be too much extra work to pull the crank and do the main bearings. You do have to be careful to watch and align the various rods' big ends when rotating the crank. I recommend putting vacuum caps over all the rod bolts to prevent banging up the journals. Installation of new rod bearings requires some manual dexterity, but it can be done.
Author:  briwill [ Sun Jun 07, 2020 10:10 am ]
Post subject:  Re: Looking for advice on slant rebuild...
Engine is completely torn down now. Measured the head CCs and got about 55. There is a pretty nasty ridge at the top of the cylinder walls so plan to take it to a machine shop later this week. Guess I will have to bore it out and get new pistons. Should I assemble the short block with new pistons to figure out the deck hight? Then decide how much to shave the head?
Recommendations on where to buy the pistons/gaskets and what brand to get/avoid?
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