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Help me make some engine teardown/evaluation/might-as-well decisions please.

davester

Jedi Trainee
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My brother has just returned my '65 Sprite (that I bought in high school and then sold to him) to me after having had it for 40 years. He had the engine and gearbox pulled a couple of years ago for the purpose of installing a new clutch and it never got reinstalled. The engine itself is a 1098cc 10CC and is partly disassembled (flywheel, head, oil pan removed) and is now on an engine stand. A compression test just prior to removal was good, with 175 psi compression all around. One minor concern I had at the time was that to my untrained ear the bottom end seemed a little noisy (mild clanking noises), but perhaps that is how they all sound. My brother said that he vaguely recalls perhaps having bottom end work done in the past but can't remember specifics. The car has around 90,000 miles on it.

Now, I am torn between possible different directions that I could go. I am not wanting to sink a lot of money into making this into a pristine engine with performance upgrades, because that money would probably be better spent buying and refurbishing a 1275 (perhaps something for the future). However, I'd like to get the car back on the road relatively soon and if I'm to keep this engine I should probably take advantage of its current state of (dis)assembly to do some evaluation and perhaps make a modest investment to ensure that it lasts a while. One thing I do need to replace for sure is the back plate, which is broken at the starter. So, I'm seeking advice on how far to go here and what things are worthwhile versus what things are overkill given my goal. Here is a list of possibilities I can think of:

1. Replace the big end bearings. This seems easy. I figure I can visually inspect for damage and measure the journals with a micrometer to see if they are undersize This seems fairly straightforward.

2. Replace the mains. Same as above but I'm wondering if I can measure them with the caps off and the crank remaining in the car. Pulling the crank is going to involve a bit more work (timing cover, etc) and now I'm heading down the slippery slope of a major engine overhaul and I would start thinking about crack checking, etc.

3. Pulling the pistons and replacing rings. Now we're into the mode of perhaps fixing things that aren't broke (given the good compression). The obvious progression here is taking the block to a machinist to measure the bores and having him tell me that I need a bore job. I'm not sure I want to go this far but would it be foolish to not even do an easy evaluation?

4. Head studs. Should these be replaced? Is there a way to evaluate them?

5. Oil pump. Pressure was good. Is there really any need to replace?

6. Evaluate the camshaft for lift using a dial gauge. The lifters look good so there probably isn't a problem.

7. Replace the timing chain and/or tensioner. I'm not sure how.

8. Rear "seal". I'm not going to buy Gerard's kit because it's too much money for a motor I may eventually switch out. However, I'm wondering if there's any work that can be done to improve the effectiveness of the factory screw "seal".

9. Anything else I'm not thinking of?

I'd appreciate receiving some opinions on these thoughts.
 

JPSmit

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My big question is how disassembled and for how long? The absence of oil on a partially taken apart motor could do more damage than an engine in the car with old oil.

I would plastigauge the bearings and check the cylinders for wear/scoring. Rings aren't expensive plus a quick hone.

I just tonight replaced the oil pump - the only thing I didn't replace when I refreshed the engine - and it has been causing me worry ever since.

Not hard to replace the timing chain/tensioner while you are there.

General wisdom is replace the head studs. Not sure about the cam.

have fun!
 

Gerard

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If you don't want to sink a lot of money into it and have in mind to upgrade to a 1275 anyway, I would inspect the bearings for signs of wear. If there's no scoring, check with Plasti-gauge to see if bearings are within tolerance. If it's not severe, I would just put it together as-is and use it.

Change the timing chain and gears if it was noisy. If you get a dual row chain and gears, that can be migrated to the 1275 later. If the head is already off, check the valves for leaks by inverting the head and filing the chambers with a solvent like lacquer thinner, and see if any liquid leaks out. If they leak, you can pull the valves and lap them yourself rather than do a complete. The tools to do that are pretty inexpensive. If the pistons are are original or are high milage, I can pretty much guarantee you you won't get away with just rings. Typically, these pistons wear in the ring lands and replacing with new pistons will be end result. Out of all the engines I've built over several decades, I've only encountered 2 that the pistons were in good enough condition to reuse. If you have good oil pressure, keep the same pump. Also, you can lap the cover and restore it to close to new condition. You say it has good compression, so I would surmise that you are probably good.

You can't restore the scroll seal function without doing a line bore. This is one of the more expensive machine charges to do, and most shops won't have the tools do do such a small engine. My shop always has to send mine out to a shop in Sacramento or Auburn for that.

If you decide to go the rebuild route, you could always disassemble everything and have them check the crank/spec the crank, and measure the bore for taper, oval and oversize wear. You really can't decide on how to go forward with a rebuild without knowing that. That alone is not expensive, but if you go ahead with the proper machine work and have to buy new parts, things will start adding up quickly.

I wouldn't worry too much about the cam or new studs unless you get ARP studs. They can be used with the eventual 1275, as could a cam if you choose to get a new, better performance cam. If you upgrade the cam, get a new oil pump that will match, as many new performance cams used the slot drive. 1098's usually have a pin drive cam and pump which is little used anymore.

Unless it's beat to sh*t, you should be able to do a minimum of tidying up and just use it until you source a 1275.

If you want to source any parts through me, I can save you some money. Since your local, shipping won't be an issue either.
 
OP
davester

davester

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My big question is how disassembled and for how long? The absence of oil on a partially taken apart motor could do more damage than an engine in the car with old oil.

About two years. Only the pan and head is off.

General wisdom is replace the head studs.

Why is this?
 

JPSmit

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About two years. Only the pan and head is off.



Why is this?

Please defer to Gerard on this (and I didn't) but, my understanding is that they don't restretch well in being re-torqued.
 

Gerard

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JP,

Were is a complete fresh rebuild, I would agree with your recommendation, and in itself, there are inexpensive ones you can buy. However, everything adds up, and the old ones would certainly be fine to get by with short term.

Please defer to Gerard on this (and I didn't) but, my understanding is that they don't restretch well in being re-torqued.
 

glemon

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I believe one shade tree mechanic way to check studs for stretch is to run a good new nut up and down the clean threads. If stretched you wiLL get some resistence/bind, which makes sense because the stretch should occur at the weakest point and the diameter is reduced by the threads. Bearings are pretty cheap, I would replace if signs or evidence of wear. If compression is 175 +/- 5 across the board I wouldn't worry about rings/pistons/bore and bodes well for good valve sealing in the head too.
 
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