Technical Engine build plan. Comments welcome.

[jjacob]

I have not been on the forum for awhile due to starting a new business. My 1969 500L has languished in the mean time. I decided that I wanted a 650 engine and transmission, but of course in the USA these are almost impossible to find or people think they are made of unobtanium.
I just recently purchased not one but two 650cc engines as well as a 126 transmission on eBay Germany. I have a friend in Germany who is going to crate everything up and send them to me.
Thought I would share my plans and get some comments and advice.
I have decided to stay with the stock 650cc displacement. I cant justify spending a lot of money for another 45cc's which will likely only yield a few more horsepower all by itself. Carburetion, head work, compression increase, and a more sporting camshaft seem to be the ticket to most horsepower increases with these engines. The cost difference between 650cc cylinders and pistons vs. 695cc is huge. Parts are way more expensive plus the added cost of machining.


So here is the plan:

1. Rebuild engine. Determine condition of cylinders and pistons. May only put new rings in with a hone if everything else looks good.
2. 35mm intake valve. Stock exhaust valve.
3. Hardened valve seats and some mild port work.
4. Sport camshaft
5. Aluminum 3.5L sump
6. Clutch disc with spring center rather than solid center disc.
7. Oil filter and cooler set up.
8. Retain existing Weber 28IMB carb with a rebuild.
9. Tubeless wheels with 135/80R12 tubeless tires.
10. Pertronix electronic ignition (currently on my car)

Here are my questions:

1. How much would I skim the stock head to get something around a 8.8 - 9.0/1 compression ratio?
2. I am thinking of getting a welded and balanced steel fan. I have heard the stock fan is prone to letting go and the aluminum ones are inefficient.
3. Camshaft - thinking a 30/70-70/30 or 35/75-75/35. I want torque. Power over 4500rpm does not interest me. I want fairly smooth idle and pulling power. Cruise at 60mph (100kph)
4. Is it worth the money to get a bis crankshaft? Car will be driven not only around town but on longer trips at constant 50 - 60 mph for hours. Is the stock crank up to that task?
5. Exhaust type: I am wanting better flow but I do not want to suffer a loud exhaust or one that drones. I am thinking of the types that either have a collector "Y" into the center or into the end. To me this is better balanced. Into the end seems better flow wise. Are they all loud other than a stock muffler?
6. Will the starter motor from my 110F engine fit the 126 engine and transmission?
7. Thinking I will keep the flywheel stock weight. Smoother idle and will dampen the inherent unbalanced nature of a two cylinder engine.

Sorry for the long post but thought it best to put this all in one post rather than spreading it out over multiple posts. Easier for people doing future searches too.
Thanking you all in advance.
John

 

[Bambino]

Hi John,

When I rebuilt my engine I splashed out on the 695 kit - rush of blood to the head, I guess.

Most of the work was in the head though - opening up of the inlet tract, 35mm inlet valves and a thin copper gasket.

I fitted a sportier cam (43/77) and a 3.5lt aluminium sump. I didn't fit a filter/cooler as the new sump should result in better cooling just by itself.

The tyres are 145/70s on 12" 126 rims. They are slightly wider than standard but offer a more modern tread pattern and better grip.

I used a standard 126 flywheel and had the engine parts balanced.

I'm not sure about the starter, maybe someone else can help.

The carby is an FZD - expensive but a bit better than the IMB. Distributor is a 123ignition from the Netherlands. I ditched the generator (dynamo) for an alternator.

I must admit that I took a lot of advice when I did all of this - mainly from a local motor cycle engine tuning business. I've rebuilt many engines over the years, but usually back to standard factory specs.
When I did this one I wanted a bit more power because I live in a very hilly area and needed the extra grunt to comfortably get up and down the hills.
I'm very happy with the results. The engine starts easily hot or cold, idles smoothly and pulls strongly.

Good luck with your rebuild. As you suggest, you can do a lot with these little motors without going over the top.

Please post some photos as you go.

Regards,
Chris

 

[the hobbler]

Hi Jacob;
Good to hear from you again---your proposed engine specs sound good, and sensible. I have a tuned 126 (652cc) engine in the back of my 500 and it will cruise at 60/65mph and tops out at just under 80mph--and that is with a re-jetted 28IMB carb. I still have some carburettor work to carry out (HS2 SU carb or a Weber 34) as my target is 80mph--with this engine. Driven sensibly the 652cc engine is pretty unburstable and should give you all the performance you want at a sensible price.
4 details---(a) the 500 starter won't fit the 126 engine--an early 126 'cable-pull' starter works and fits fine.
(b) you will have to fit 500 (25mm) drive-shafts to the gearbox--the 126 'shafts are too long
(3) the 500 flywheel is 2kg (about 4-1/2lbs) lighter than the 126 flywheel and bolts straight on
(4) spend some money on getting the whole crank/rods/pistons/flywheel/clutch/front-pulley assembly balanced. It is stupid spending money on a rebuilt engine and then watch it shake itself to death!
I hope this info is of use to you---keep us all updated as to progress please

 

[Toshi 975]

Hi JOHN , I have to agree with the other guys so far and I think that you are on the right track for what you want to achieve. In fact your intended spec pretty much matches up to what I am running in my 126 and it goes very well even with the standard carb but I will be upgrading to a twin choke later this year. I have had no problem with the alloy fan even when driven hard for a long run in the summer heat. I am running a Bis crankshaft partly because I got my hands on a good one for a reasonable price and also I wanted to try one when some pals said it would not work. I have not gone for balancing and have not had problems with a number of rebuilt engines.
I am running +0.060" pistons which give 662 ccs and I have avoided head skimming so far but used thin copper head gaskets which are about 1mm thinner than standard. Depending upon the age of the engines you have bought if they are later ones they will have unleaded valve seats and the better combustion chambers.
As you have a 500L you should already have a pair of the thicker drive shafts that you will need.

 

[jjacob]

Chris, Tom and Toshi thanks for the replies.

Tom, 80 mph in a 500? You are more brave than I!

My engines and transmission do not have a starter motor so I will have to buy one.
I am thinking that I do not need a bis crankshaft for long term durability with the type of driving I would be doing which is mostly around town but with some highway (60+ mph) for hours on end. Does that sound correct?

Are you running the original style solid center clutch disc or the aftermarket spring type?
I am thinking the spring type would offer smoother engagement and be less harsh on the transmission and engine. Thoughts?

Are the copper head gaskets all thin (to raise the compression ratio) or do I need to make sure I get a specific thickness?

I know the 126 transmission is geared so there are a little less rpm at speed, but my thoughts are that the 135/80/12 tires will give me another 3% reduction in rpm for more relaxed cruising and hopefully not have any fender rubbing issues.

Again, thanks for your comments and benefit of your experience.

John

 

[jjacob]

Just did a little poking around on the internet. 0.5 mm thick copper head gasket is the one to get to raise the compression ratio. The other thickness normally supplied is 1.5 mm.
John

 

[Bambino]

I think the two commonly available standard head gaskets compress to 1.2mm and 1.5mm respectively.

Chris

 

[Bambino]

A bit of rough maths:

652cc engine has a bore and stroke of 77 & 70mm respectively giving a swept volume to the top of the cylinders of 652cc. Standard CR is 8.0:1. This gives a calculated volume, including gasket, at the top of the combustion chamber (in the head) of 652/(8-1) ~ 93cc. Total chamber volume (2 cylinders) is therefore 652+93 ~ 745cc.

With a 77mm bore, a 1.5mm gasket encloses a cylindrical volume of ~14cc leaving ~79cc in the head proper.

Fitting a 0.5mm gasket adds 14/3 ~ 4.6cc of volume. The new inclusive volume in the head is now 79 + 4.6 = 83.6cc.

New CR is (652+83.6)/83.6 ~ 735.6/83.6 ~ 8.8:1

For a 9:1 CR engine the exhaust to inlet valve diameter ratio should be 0.8.
Your inlet valve should be then 28/0.8 = 35mm. Winner

Rough and ready, but works for me

Comments and corrections gratefully accepted,
Chris

 

[jjacob]

Chris,


Thanks so much for the reply. You were obviously paying attention in math class!
The gaskets you referred to in your previous post at 1.2 and 1.5 are the fiber and steel "normal" head gaskets. The ones I referenced were the copper sheet type.
8.8 compression ratio is perfect. Thanks for doing the heavy lifting for me! I will target the 0.5 mm head gasket with a 35 mm intake valve and some mild head work as you have done to your engine. Based on research I have done on this forum and others, there is no need to change the exhaust valve.
I will need to check and see the age of the engines I have. The earlier 650 engines had a compression ratio of 7.5/1 the later engines were 8.0/1 as you state. Below is some information I found on a 126 web site.

"FSM then undertook a program aimed at improving the fuel consumption of this already frugal little car. Extensively modified prototypes were created but they proved too expensive to put into production. In November 1982 the 650E was announced and this received a new exhaust, modified combustion chambers, and revised ignition settings. This resulted in an improvement in fuel economy of 7%. Further changes were made to this model in June 1983 which included a compression ratio of 8.0:1 (up from 7.5:1) and revised valve timing. This gave another 5% improvement in fuel consumption."

Best regards,
John