Technical Plans for 650 engine and transmission rebuild

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Technical Plans for 650 engine and transmission rebuild

jjacob

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Location
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I have been off the forum for awhile now, but am now ready to start the conversion of my 1969 500L to a 650 engine and transmission. Got a few personal emails from the Hobbler last year which were informative. I am in the USA (Nashville, Tennessee).
I was able to buy two 650 engines and a transmission out of Germany (ebay). Basically there really are no used 650 engines or transmissions available in the USA or Canada. Those people that have them here seem to think they are made of Unobtanium. Got both engines for $370 which included shipping within Germany and the transmission for $190. Shipping to USA was free as a customer allowed me to put them into their container! Both engines turn free and are 100% complete (alternator, carbs, clutch, all sheet metal).

I want to go over my general plan with the forum. I want to keep this economical so I will be keeping the stock displacement. Most benefits in torque and horsepower seem to come from cam, intake valve and compression increase changes rather than a 50cc increase in displacement.

Engines are both FSM (Polish):
Engine #1
FSM 126A1.076/8 6739534
Head: AD84M "650"
Carb: 28S1A-1-250 (has 2/98 stamped on carb. Date code?) has 2 vacuum ports in carb spacer.
Has wasted spark distributor (no cap or rotor)

Engine #2
FSM 126A1.076/8 6664664
Head: AD84M "650"
Carb: 28S1A-5 (has 10/96 stamped on carb. Date code?) has no vacuum ports in carb spacer.
Has standard distributor (rotor and cap)

Transmission
Fiat 126 AB.0C.1
4321651 10A

I have searched the internet and cannot find any information that gives a range of engine serial numbers and the year they were made or any differences. What I have been able to find out is that these engines are most likely from 1984-1994 based on the .076/8 in the engine code. These later engines should both have an 8.0/1 compression ratio? Wasted spark started in 1985, so that makes the older engine 1984 or earlier?
Any information about either of these engines would help.

My plan, other than to do a complete normal rebuild, is to maybe keep the existing cylinders and have them bored to 0.40mm oversize. I can get a new old stock Mahle oversize piston kit out of Italy for a reasonable price. This keeps costs down and slightly (very slightly) raises the compression ratio. I would increase the size of the intake valve only and keep the standard 28 carb for right now. Use a new cam with something like a 35/75 75/35 profile. Add an oil filter/cooler take off to the front engine cover. Thinking about using the wasted spark distributor and replacing the points with the Pertronix system I have already installed in the 500L. I would like to get to a compression ratio of around 8.5/1, so was thinking either milling the head 1mm or using a thin head gasket. I have a set of aluminum 12in wheels and new 145R7012 tires.

Transmission will be gone through. At a minimum new seals. Gears and syncros will be examined for wear and replaced as needed. Already have a brand new starter motor.

So please give me your opinions. Keep in mind I do not want to spend tons of money on this. Reliability is number one. Second is the ability to cruise at 80-95 kph (50-60 mph) for long periods of time and have more power for going up hills and accelerating from a stop, etc.
Also any information about the differences in the two carburetors or differences between the two engines would be appreciated.

John
 

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If I may say your ideas may struggle to realise some of the gains you desire.


The original engine only revs to 4700rpm and to have an engine that cruises at the speed you wish, you will sit near the top end of what you engine can rev to.


A change of final drive ratio in the diff will assist in bring the revs down a little - but balancing the internal components ( maybe lightening some) would enable higher revving unit.
Bigger inlet valves will help along with porting and polishing - maybe a cheap sports exhaust - with the exhaust elbows machined to match.
BUT beware of milling the head - you will remove the gas ring that is the safety escape of gasses should the gasket fail.
If the surfaces are prepared correctly you can run without any head gasket - as I do - but you need to be aware of the pitfalls.
You could remove some material from the base of the barrels - bringing the pistons crowns closer to the head - but this is dependant on what concoction of parts you are running.
 
It all depends on what you wish to do with your 500.
Have you driven one? If not, drive one first before deciding what you are going to do with it.
If you are keeping the vehicle in standard form, ie. wheels & suspension set up. Then the standard 650 engine in my opinion is suffice for this little car.
If you plan on upgrading the handling of the vehicle then the list of modifications is endless depending on your budget.

I used to modify Mini's when i was younger to the point that they were probably dangerous to drive - I wrote 2 off and nearly died, but the thrill always seamed worth it.
Today i am older, wiser and enjoy life, so i am quite happy driving my little baked bean tin on wheels at a slower pace with the knowledge that this car was not built for speed or safety in mind. I have a modern car for motorways and speed.

The 650 engine is quite a poky little engine and im sure with a few little tweaks you can make this engine a little bit quicker without too much cost or affecting its reliability. There is always a trade off with engines!
 
It all depends on what you wish to do with your 500.
Have you driven one? If not, drive one first before deciding what you are going to do with it.
If you are keeping the vehicle in standard form, ie. wheels & suspension set up. Then the standard 650 engine in my opinion is suffice for this little car.
If you plan on upgrading the handling of the vehicle then the list of modifications is endless depending on your budget.

I used to modify Mini's when i was younger to the point that they were probably dangerous to drive - I wrote 2 off and nearly died, but the thrill always seamed worth it.
Today i am older, wiser and enjoy life, so i am quite happy driving my little baked bean tin on wheels at a slower pace with the knowledge that this car was not built for speed or safety in mind. I have a modern car for motorways and speed.

The 650 engine is quite a poky little engine and im sure with a few little tweaks you can make this engine a little bit quicker without too much cost or affecting its reliability. There is always a trade off with engines!

Very wise and sensible advice from Sean...especially drive it first and see what you think.(y)
My car can and does "cruise at 50-60 mph" all day (well, for up to three hours at a time) giving allowance for inevitable slowing down on hills. And that's with an unmodified 499cc engine.
I think too many cars are bought with tired engines which give a very poor impression, but putting the same amount of attention as you tuning experts do and a lot less stress and money, into simply renovating it back with standard components has made a very nippy car with great reliability as designed.
Same applies to brakes and suspension/steering. The car is a giant go-kart....what needs fixing? It's pottie! :D:D:D

MAL_9012 by Peter Thompson, on Flickr
 
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Sean and Peter,
Thanks for the replies. I already have a 1969 500L that is 100% stock. Engine runs great, although a little tired, and brake system has already been rebuilt. Rather than rebuild the 500cc engine, I think it is better to rebuild a 650. As I said, I am looking for a little more acceleration from a stop, more power up hills, and able to cruise at 50-60 mph. I think the 650 engine and transmission will do that for me.
John
 
Andrew, do you have any recommendations on a final drive ratio? Maybe a good compromise between acceleration and cruising rpm?
I agree about milling the head, not my first choice, although you can mill the gas ring back in. All of the suggestions you made on cleaning up the heads and exhaust are things I intend to do.
John
 
Andrew, do you have any recommendations on a final drive ratio? Maybe a good compromise between acceleration and cruising rpm?
I agree about milling the head, not my first choice, although you can mill the gas ring back in. All of the suggestions you made on cleaning up the heads and exhaust are things I intend to do.
John

Hi John
I would stick with the 126 drive you have. The only other option is the higher ratio Bis diff which may be a bit sluggish on a modest power upgrade. I have just had a head skimmed by 2mm and as you point out the gas ring can be easily recut. I am told that I will have about a 9.1 compression ratio +or - depending upon head gasket and that is compatible with a sport camshaft. Also been gas flowed on the head and inlet manifold for a twin choke Weber. I had one head worked on by a motor cycle racing specialist and he was confident in getting 2-3 hp more from each cylinder with the porting so if you can do your own tuning there is quite a bit to gain at not too much cost :)
 
Thanks Toshi, maybe I will have the head milled then when all the other work to the head is being done. I will have to see the condition of the heads on these engines to see if they have been skimmed previously. 9:1 would be the maximum compression ratio I would want. I'll do a little more research on head gasket thickness / milling amount and resultant compression ratio.
John
 
Just a quick hint - these heads are prone to crack between the valves - check before works commence
 
hi John;
I will go through your notes carefully and e-mail you direct with my considered advice. With a mild tune and careful rebuild, a 650 engine can run reliably at 55-60mph, no problem---don't forget, you are talking basically about a 126 in 500 clothes. What will also help will be an increase in tyre size as this will effectively increase you diff ratio, which an even mildly tuned 650 engine will easily pull.
I have a well tuned 652cc 126 engine (36 bhp at about 5,600rpm) in the back of my beastie, and she keeps up with traffic with no problem. On none-main roads she is probably driven as fast as my 'normal' car (a Citroen estate), if not quicker if I am feeling mischievous.
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Hello jj, I am in the middle of an upgrade to my engine and if I can give you any advice it would be to measure the volume of the individual cylinder to determine the the actual compression ratio before you start cutting any metal off. It will then be a simple job for your engine shop to calculate the amount of volume required to achieve the compression ratio you need. Using either no gasket or one of the various available will help. I have found that a volume of 34.9cc will give just above 9.5:1 with a 1.2mm copper gasket. But, this is using a 704cc engine, so your calculation will be slightly different. As always make sure the bottom end of your engine is sound too. If you have any questions ask.

Ian.
 
Well I finally got around to starting my engine build. I have modified my plan somewhat in order to save some money, mostly because the engine was found to be in better shape than I expected. The engine I am rebuilding is a wasted spark engine. It appears to be from 1987 based on a casting mark on the timing cover.
I have completely torn the engine down and found the cylinder bores to be in excellent condition with almost no wear. Same with the pistons. So I will hone the cylinders, clean up the pistons and put a new set of standard rings on with new standard rod bearings.
Likewise the crankshaft measures perfectly with virtually no wear. Only the two crank bearings show just enough wear to be slightly out of spec. So I will replace those.
Engine block is in great condition as well.
Here is the new plan:
-New standard rod and crank bearings
-New standard front and rear crank bearings
-New standard piston rings.
-Have hardened valve seats installed in head
-New valves - 34 mm intake, standard 28mm exhaust
-New valve springs
-Mild porting to intake and exhaust on head and on exhaust elbows
-Replace wasted spark points with my Pertronix unit currently in the 500 engine.
-Replace metal fan with cast aluminum fan
-Install 3.5L cast aluminum sump
-Install oil cooler and filter (no cost as I already have these parts from an old Saab)
-0.50mm copper head gasket to raise compression ratio slightly. These later 650 engines are already 8.0/1 compression ratio
-Mild cam, maybe 30/70 or 35/75 with new cam followers, or should I just stay with the stock cam? Cam number is 7541011 SF 4/8. I know Fiat modified these later 650 engine cams for better economy and a little more power.

Only issue I found was with the exhaust valve guides. One is high and the other is low. Both intake guides are at the correct height. What do you think caused this, or is this something you guys see all the time? I cannot physically move the guides with my hands and both valves and guides are in perfect condition with zero wear. Picture attached.

Your opinions and comments are welcomed and valued.

John
 

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Evening John;
Great to hear that you have at last been able to start on your engine. Your list of work sounds very sensible, and cost-effective vis-a-vie money spent against performance gained. The heads on the 500/126 engines are not the best design for air-flow, so carefully porting them (especially the ridge behind the inlet valve) can be very beneficial. A 35/75/75/35 cam is as 'wild' as you want to go. Get yourself a decent exhaust---Middle Barton Garage market a good, strong, single pipe sports exhaust---mine has been on for 2 years with absolutely no problem. Don't forget to carry out the exhaust-mount mod that I mentioned in my notes to you (it is actually a 'pukka' Abarth mod). If you have any problem with the bolts that secures the exhaust manifolds to the head, change the system to studs, again as per my notes. Irrespective of how good it looks, I would put a new clutch in whilst you have the engine in pieces. The Pertronix ignition system is a good system and should give you no problems. The drive shafts will need to be changed to 25mm Fiat 500 shafts (the 126 shafts are too long). Carb jetting; I would leave it standard to start with and see how it runs--you might have to go up 1 on both the main and the slow running jets. The combination of a 126 diff and slightly bigger tyres will help in slightly reducing the revs per mph. If I can help you in any other way, you have my e-mail address, feel free to use it.
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John;
Sorry, forgot to answer your question as regards your exhaust guide. The situation that you have is not correct. Look into the exhaust ports, I expect you to find that 1 guide is poking into the air-flow a lot more than the other. I would recommend that you get an engine shop to look at that (or use the other head)
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Thanks Tom, I intend to install a new clutch kit. I also intend to replace the entire drive shaft and assorted bits and pieces with new, even though my 1969 500 has the right size axles to fit the 126 transmission I have.

What do you think about the exhaust valve guides? I am sure I could drive them back into correct postion, but would not want them to move again. Am I looking at installing new oversize outside diamter guides for the exhaust?

John

I replied too quickly! Thanks Tom.
 
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Hi John, you might have seen that I just completed the same job on an engine from 1986 myself. I had to change the cam because one of the lobes was worn and I discovered that there is a one camshaft fits all approach from most suppliers. So if yours is good I would hang on to it. If you get a new one I would also splash out on new cam followers. I did and I am sure it is contributing to the rebuild making for a very smooth engine.
I suspect that your valves have seized in the guides at some point so it is worth a thorough check that there is minimal play with the new ones and that the guides aren't scored.
I think that the guides would originally have been pressed in and there was also a Fiat tool which is a stepped drift. If it was mine I would use the old nut, bolt, tubes and spacers technique to pull them back in place, but new guides are easily and cheaply available so perhaps you could go for them. I'm not sure but I think that with new guides you might be supposed to lightly recut the seats but if you're getting new seats the whole job wcould be done in one go.
 
Hi Peter, I actually just read your rebuild thread 30 minutes ago!
The exhaust valves momentarily seizing in the head would explain the odd positioning. I will take another look at the exhaust valves and guides, but they seem to both have virtually no wear on them. I'll see how easily they move back into position.

I really think that these later 126 650cc engines are better. Like I note, both the camshaft and compression ratio was improved giving better performance.

John
 
Well I have consulted the Haynes manual and they show that the valve guides should be installed such that they are nearly flush with the inside wall of the air passage. So in my picture the exhaust valve on the left is the only one installed correctly. All others have been driven in too far. I have a tool to drive them. I have driven one back to the proper position. Believe me they are tight! So I am not worried about them moving. It may be that the head had new guides and valves installed many miles ago and the guides may have been improperly installed.

All guides and valves are in great shape both dimensionally and surface smoothness.
John
 
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