Engine rebuild (questions)

[phaetn]

@OP

Any particular reason to stick with low cr pistons? Seems a good opportunity for some extra power.

My one true concern is that that the head was decked when it was rebuilt two years ago. I'm worried that any excessive dome might cause interference, and the 10.8:1 have an 8mm dome height compared to 1.25mm for the 8.8:1 (true for both A/R and Vick's).

I'm having a tough time determining if the head I'm using now was originally from a 1756 or 1995cc engine. It's numbered 4372291 with other markings of 34AS.6C (no "1" before it) so, according to Mirafiori's Head Casting ID, it could be from a '77 Spider 1756 (if the other marking was a 134AS); OR it could be from a late 1995cc Spider. My other head, which hasn't been rebuilt and would create an added expense to get valves seated, etc, is numbered 4277590 and is, fittingly, from '74-'76 Coupes, Spiders, and Lancia Betas.



Stock for my car was 8:1 and it's probably running less than that, so 8:8:1 would be an improvement. I also don't want to tax any components too much. I've really had issues with coolant leaks and don't want to pop another head gasket. That said, if it's getting machined it should all be top-notch fitment, right?

I suppose I would prefer running on regular rather than premium gas, too.

Geez, if I go for high compression pistons, then I'll have to get bigger brakes, a limited slip diff and all sorts of other things, too.

Cheers,
phaetn

[SteinOnkel]

You can measure and determine if high cr pistons would fit.

In any case, I wouldn't discount it. Compression ratio is the most vital component for an n/a engine in terms of how much power it produces.

[aj81spider]

It looks like it's a 1756. Here's one for sale on Ebay. Page forward and there's a shot of the numbers. They look just like yours:

https://www.ebay.com/itm/Fiat-124-Spide ... 3203159576

It looks like you have the air injection ports which weren't on the 1995.

http://fiat-spider.com/f15/viewtopic.php?t=35548


However I'm not much of an expert so if someone else knows better trust them!

[18Fiatsandcounting]

Based on the evidence so far, I agree that it looks like a 1756cc cylinder head. As pointed out, casting numbers can be a source of confusion, and common examples are the cylinder heads and transmission case parts.

Keep in mind that a lot of driveability is where the power is produced, not the ultimate HP at 6500 rpm or so. When I did the conversion in my '69 spider from the 1438cc to a 2L engine, the overall power didn't increase (maybe it's even lower), but the car feels so much stronger because you don't have to flog it like a rented mule (in terms of rpm) to get it going. I agree that raising the C.R. will increase the overall power curve, but you can also look at carb and cam options to flatten out that curve if you so desire.

-Bryan

[phaetn]

Thanks - that's a great help!

Cheers,
phaetn

[Nut124]

I would measure the chamber volume. 1800 head is supposed to be 49cc. 2L heas 54cc. Surfacing reduces chamber volume. I could share data and methods. This is the only way to determine actual CR accurately.

Head gasket thickness is a factor.

A dry build with modeling clay is a good idea when building with non-stock pistons and/or cams/valves. This is done to examine internal valve to piston clearances, both axial and radial.

I would not go above 9.5, 10 unless you plan on optimizing AFR and ignition timing and/or like living on the edge.

[phaetn]

Thanks for the reply and offer to share methods. Good tip about the clay testing.

To be honest, I'll just leave the head I have now it the way it is, even if it has slightly greater volume, and therefore less compression. It would be an added expense if I went with the other head that has valve guides that would need to be removed (too much slop against the valve stem). The one I have now is set up right. I think I recall reading somewhere that the difference between the two affects static compression by .02 (i.e. if it was 8.8:1 with an 1800 head then it would be 8.6:1 with a 2000 head).

I now use a stock paper head gasket having once tried an MLS gasket from Allison's trying to solve a coolant leak. I ran it once and then took it out right away since there was still a leak. I still use his stud kit for extra clamping force. The machinist, apart from boring the cylinders, should match the block and head, too, though I know that any shaving will reduce the compression area and run more risk of interference.

A/R sells:

• 10.8:1 (8mm dome height) and 8.8:1 (1.25mm dome height) piston sets for the same price @ $200.
• 9.8:1 (4mm tall dome height) is nearly double the price at $380 -- not sure why - if just a different supplier or what.
• Or they have a built to spec forged set at $800 that I will avoid (can be 10:1 or other ratio).

Vick's sells (all for $190):

• 10.2:1 set (10.4:1 on an 1800) for $190 (compression Height: 38.70mm; 8mm dome height);
• a pop up set with no compression listed (compression height: 39.65mm (stock Fiat pistons are 38.70mm) - I don't think there are domed, just a taller overall height (so I should avoid these with a decked head);
• a Stock+ set (compression height: 39.00mm; 1.25 dome height) but employ custom rings (probably the same suppler as A/Rs) I suspect these are also 8.8:1 since stock 1974 was 8.0:1.

It would be nice to just have the engine buttoned up and then not have to worry about it again for 20 years. I guess that's pointing to the 8.8:1 route. My '74 came stock with 8.0:1 compression so even this would be a gain.

The car already has decent enough power, but just a tired engine, so even fixing the blow-by would get a boost, not to mention going to 8.8:1. Then add a mild intake cam to help with top end power and that should be good enough. As it is, I can easily slip the inside wheel on 90° corners (with 205/50-15 Direzzas) and I don't need to be power sliding all over the place. While I love the wheels, the tires give *no* audible warning when they're on the edge (no squeal at all when cornering or lighting one up on acceleration) -- they just let go.

I was planning to put in an AFR gauge, too (hidden in the glove box) to actually dial it in right at the carb with my mixed and matched components. Ignition timing I just do on my own with a timing gun on the Computronix waste spark system.

Thanks again!

Cheers,
phaetn

[Nut124]

I have an extra set of the 4mm dome pistons. I had them installed in my short block on the stand, but took them out and went to the 8mm domed because my 1800cc head had a bad valve seat and I went with a good 2L head.

They are in the 1st oversize, 84.4mm. I will likely never need them. I might have a set of rings as well as I ended up going w a custom ring.

In general, I think that the pistons sold by Vick and AR are the same pistons in terms on CR and specs. There is dished, flat, 4mm and 8mm. As far as I know, they are made in Brazil to OEM spec by Borgo(?).

[phaetn]

Thanks for the offer, Nut124. I think 4mm is the way to go for me. I'll have to go for A/R's complete rebuild kit so as to get all the bearings, thrust washer set, etc. I don't want so show up at the machinist's with mixing and matching bits and bobs and end up missing something. I'm still undecided if I should have the machinist's do it all (including buttoning it up), just bring it to them for the boring/honing and have a very experienced friend do the reassembly, or if I should tackle the latter myself. I don't have a heated garage so that's a real deterrent.

To that end, does this engine stand look like it would work? Princess Auto is like your Harbor Freight: a lot of stuff at low cost, often low quality, but good enough for situations where there isn't commercial use.

Description here: https://www.princessauto.com/en/1500-lb ... 0008682817
I might use it myself or just give it to my friend to make his life easier.

I went through my stock of goodies from past orders and it turns out I still have an unopened MLS head gasket as well as a new Fel-Pro traditional style. A/R doesn't seem to sell it any more and I wonder what makes it "performance."


I also still have gaskets for the water pump, etc. The pump was new as of two years ago so I don't even know if I'll change it out.

Thanks again for all of your advice!

Cheers,
phaetn

[dinghyguy]

My two cents worth....
The princess auto stand will be fine, and look good in the warm family room where you reassemble the engine after everyhing is machined and clean.......although if you take it over to your friend (spiderdan?) he will not be able to stop himself from working on it even when you are not there.....which is a good plan if you are as lazy as i am!

If you have not thought of it, you might want to mount the block sideways on the stand to give you good access to both ends as you proceed.

I would also take the water pump off, just to make it possible to clean the block without worry about bearing contamination
Are you going to replace the casting plugs in the block as well?

Also what about oil pump are you going to replace, and fuel pump are you going to change to electric (or have you done it)?
If you are changing the fuel pump you may want to take the lobe off the shaft that drives it.

And of course painting

Oh, while the engine is out you might want to remove the main crossmember and confirm there are no cracks in the frame under the mounting bolts.
I am sure other scope creek suggestions will come from others...

cheers
dinghyguy

[Nut124]

The Fiat twincam is a very simple engine to assemble.

If you take the block to a shop, tell them not to acid tank it or the aux shaft brgs will get eroded. They are not easy to replace.

[phaetn]

Thanks for the great tips.

dinghyguy, it's another Dan (CanadaDan) that will be be helping me out. I don't think he's on these boards any more. He used to be THE Fiat guy in town with a shop years and years ago, and still has containers full of parts. Unfortunately they are not inventoried so it can be a bit of a treasure hunt to find things. He has a wealth of experience, too, but it a ways out of town and what with COVID and all, we are not supposed to mingle. Still, car repair is considered an essential service.

CanadaDan has an assembled 2.0L motor that he has tried to tempt me with in the past but I'm already concerned about the low height of my oil pan (I have a dropped suspension) and would, frankly, rather keep the appropriate serial number for the block that matches the car. I know that's probably stupid since these cars aren't really that valuable, but I hope to keep in another good 20 years or more and maybe by then it will have appreciated even more. If we will still be able to buy gas.

A few things I was thinking about as engine is pulled:
- grind off lobe of auxiliary shaft (I have an electric fuel pump, but still have not installed a FACET high quality one I have lying around)
- plug coolant passages in the head that lead to intake (I have an electric choke) to reduce possibility of sucking coolant
- grind some meat off the back of the 95w alternator as it doesn't quite line up with the block (belt at a slight angle)
- check out the crossmember condition and attachments
A little over four years ago I had one of the control arm bolts fail after an alignment so I replaced them with longer ones (an issue because of the lowered suspension) so I want to give it all a good look-over and replace the ones on the other side, too.
https://www.flickr.com/photos/1974_fiat ... otostream/
- I'll have the block painted, too, if I'm bringing it to the machinist's

Once it's out and apart CanadaDan will tell me what I need. I'm not going to order anything yet.

While I'd love to have it in the house, that just ain't happening. I once had a 150cc Vespa engine (you can carry them by hand) in the basement and even the fumes from that was enough to get me a scolding. I cannot imagine the grief from a 1756cc block in a stand dripping all over the place.

Thanks and cheers,
phaetn

[jon8christine]

Are you going to replace the casting plugs in the block as well?

Also what about oil pump are you going to replace, and fuel pump are you going to change to electric (or have you done it)?
If you are changing the fuel pump you may want to take the lobe off the shaft that drives it.

I'm in the rebuild process right now too...do you NEED to replace the casting (freeze?) plugs when rebuilding? Nothing leaks right now.

Also, my car had already converted to an electric fuel pump in the trunk. Are you talking about taking the lobe off the aux. shaft? Why would you need to? Just to reduce the possibility of interfering with the rod or can it break without the fuel pump on it or just to reduce weight?

https://drive.google.com/file/d/18PBMRv ... sp=sharing

[18Fiatsandcounting]

Also, my car had already converted to an electric fuel pump in the trunk. Are you talking about taking the lobe off the aux. shaft? Why would you need to? Can it break without the fuel pump on it or just to reduce weight?

My suggestion is to leave the auxiliary shaft as is, and just make sure that your auxiliary shaft pulley (and thus the shaft) is timed correctly relative to the crankshaft rotation. The issue is that that lobe can hit one of the connecting rods (#3 if I recall) if the auxiliary shaft is timed incorrectly. In other words, get all pulleys timed correctly, and you'll be good.

-Bryan

[Nut124]

Are you going to replace the casting plugs in the block as well?

Also what about oil pump are you going to replace, and fuel pump are you going to change to electric (or have you done it)?
If you are changing the fuel pump you may want to take the lobe off the shaft that drives it.

I'm in the rebuild process right now too...do you NEED to replace the casting (freeze?) plugs when rebuilding? Nothing leaks right now.

https://drive.google.com/file/d/18PBMRv ... sp=sharing

If the block plugs are in good shape they do not need to be replaced. I just did my engine and left them in place. If you take the block to a shop, talk to them about what you want to do. I also left the oil galley plugs in place but we spent extra time flushing the galleys in solvent bath. I had replaced all plugs during a past rebuild.