80cc DOHC V8

[pat1967]

Hi Guys,

I received the material for the pistons the other day, so went about making up the piston blanks during a few hours I had to spare in garage. Firstly, as there were 8 pistons, I wanted to try and minimise doing multiple setups and measuring, and couldn't really justify making a jig. So I went with the approach of machining a stub, that I could pickup in the collet chuck to turn the final diameter.

First pic shows the blanks (1" diam) all machining to exactly the same length to provide the first reference surface.

Next pic shows the machining of a 1/2" stub, using a saddle stop to provide a reference shoulder, and also something to grab the piston with to turn down the final diameter.

 

[steamer]

Great Start Pat!

Dave

 

[pat1967]

I turned the OD down of each piston to 25mm OD (final diameter will be 24mm). I mounted the first blank and zero'd against the back vice jaw, and picked up on the diameter to get my centre position for the wrist pin. I used this point as the home position, and zero'd the mill on it so I was set to go when the next blank went in.

The rest is centre drilling, drilling through and final reaming of the hole. Without removing the blank I milled out the first cheek of the piston. Same operations were carried out to the remaining 7

 

[pat1967]

With the first cheek machined, each piston blank was returned to the vise (machined cheek down) and using a blank drill rod inserted through the reamed hole, ensured the hole was truly vertical.

Vice was locked down, and the second cheek machined. I now have my 8 blanks waiting to be hollowed out (will be doing that bit cnc). The final diameter will be machined after I bore my cyclinders. At least this way I figure the pistons will be all but done.

Till the next installment ..

Pat

 

[pat1967]

Thanks Dave,

It's spent long enough in my head and solidworks, definately time to make some chips.

Pat

 

[LongRat]

Pat, this looks exciting. Have you been covering the design etc in another thread? If not it would be great to hear some more background and maybe see some CAD renderings. Also, what's the alloy you have chosen for those pistons?
Cheers.

 

[stevehuckss396]

Looking forward to watching this one take shape. I am also building a V8 so this one is of particular intrest. With 1 inch pistions I am assuming roughly 1/4 scale?

 

[gbritnell]

Hi Pat,
Nice start on your pistons but I have a question. Why did you cut the side clearance so deep? It doesn't look like it will give you much wrist pin support when you cut out the inside. I know on a full sized piston the side relief seems much deeper but then you're dealing with much bigger diameters.
gbritnell

 

[pat1967]

Pat, this looks exciting. Have you been covering the design etc in another thread? If not it would be great to hear some more background and maybe see some CAD renderings. Also, what's the alloy you have chosen for those pistons?
Cheers.

I will post up some of the renderings. The design started off as the Schillings V8, I drew most of the engine up more than a year a go, but didn't really like the crank design which was a multipart cranks shaft bolted and pinned together. I've remodelled the crank as a single piece and made the adjustments to the block to suit. Also splitting the sump, so that the upper half forms a girdle.

The pistons are being made from 6061 T6 alloy, based on what I've managed to find on the net seems to be a reasonable choice.

I've attached a couple of renderings of the pistons and the crank, conrod, piston, cylinder and block assemblies

Pat

View attachment SV8-0051.pdf

View attachment SV8-0051-Underside.pdf

View attachment Engine Main Assembly.pdf

View attachment Engine Main Assembly - 2.pdf

 

[pat1967]

Looking forward to watching this one take shape. I am also building a V8 so this one is of particular intrest. With 1 inch pistions I am assuming roughly 1/4 scale?

Hi Steve,

It's roughly quarter scale with a 24mm Bore x 22mm stroke, the length of the raw block itself is 162mm (I'd post pics of it, but I've only been game enough to rough it so far so it's a kinda v shaped billet. I want to test my cnc on a lump of wood first before I cut the water water jackets and bores on the real thing).

I've been watching your thread too, all along I was thinking how I was going too find and hold the square billet in V blocks large enough, then saw how you machined the under side of yours using the banks themselves to provide a perfect 45! I used the same method to rough the underside.

Pat

 

[pat1967]

Hi Pat,
Nice start on your pistons but I have a question. Why did you cut the side clearance so deep? It doesn't look like it will give you much wrist pin support when you cut out the inside. I know on a full sized piston the side relief seems much deeper but then you're dealing with much bigger diameters.
gbritnell

Hi gbritnell,

I probably could have shyed another millimetre to the wrist pin bosses, as they stand, they are 5mm each in length, the conrods themselves have a bearing area 6mm long. I figured considering each side would only be taking half of the load, the pad should be adequate, it also allowed for a comfortable margin to secure the wrist pin with circlips rather than relying on a press in pin or teflon ends.

It doesn't look so extreme when modelled

Pat

 

[LongRat]

Very nice indeed.
I really like the look of the Schillings engines - in fact I just placed an order for his book.
What aspect of the pinned crank do you not like? The fact you can use ball races for the main bearings always seemed so attractive to me.

 

[coopertje]

Hi Pat,

Nice project! I have a V8 on my to do list, too bad daily work costs so much precious hobby time... I was wondering about your machining sequence. Are you not afraid that you get cutting marks on the surface of the piston due to the already made cut-outs in the side? In my (limited) experience I get a better finish when there is a constant "load" on the tool.
Keep the pictures coming!

Best regards Jeroen

 

[pat1967]

Hi LongRat,

I like them too, you'll enjoy the book, not sure if you can read German or not, but as they say a picture says a thousand words, and provides LOTS of inspiration! For those interested the ISBN is 3-88180-133-2. If you love the Schillings designs a guy by the name of Rolf Luther has developed the design further (I'm striving to build an engine similar to his F1 "inboard", you can visit the website here http://www.luther-modellmotoren.de/

Whilst I do like the idea of supporting the crank on ball bearings, my reservations regarding the original built up crank are based on the fact that I could not envisage myself being able to accurately press fit all the individual pieces making up the crank. So I opted to go with a solid crank, no doubt it will be a long winded machining affair but I don't plan on finishing this motor in a weekend. The other thing is the original crank is a flat plane crank, I wanted a cross plane crank to give that lumpy exhaust note.

Pat

 

[pat1967]

Hi Jeroen,

Thanks for the comments, work always interferes here too, you're not alone!

I'm not exactly sure how the final machining of the piston OD's will go. The blanks as they stand are oversize by 1mm, and figure on taking several very light passes with a keen HSS bit to bring them to the final OD. Going the other way round and machining the final OD first, in my opinion would be more of a risk of damaging the surface, in my opinion.

Pat

 

[pat1967]

I got a couple of hours in the garage again tonight and machined up the wrist pins (no pics of the process, nothing fancy just straight turning). I used some 6mm silver steel, hardened and tempered them. I was a bit concerned about fitting the circlips and being able to remove them if need be (panic on my part) but a quick trial fit on one of the pistons put that to rest.

... Finally some finished parts!

Pat

 

[coopertje]

Hi Pat,

Nice work on the pistons! The time will learn what the best method is, and probably there are more ways leading to Rome. I normally make the cylinders first, then turn the pistons to meet the cylinder boring because I find it more easy to get an exact measure on external turning then on a internal one (hope you understand my crapy English).

Just read that it will be a Schillings engine, cool! I have the book and the drawings for the 6-cylinder line and V8. I totally agree on the crank design. For the 6 cylinder I made the crank from separate parts, but in a different way. Made steel disks of 12mm wide and 35mm in diameter. In all of them I drilled (and reamed to 10mm) a hole in the center and 3 ones on the correct pitch circle in 120 degrees. From 10mm silver steel I made the crankpins. When assembling the parts I took a long 10mm rod and run it trough the center of the disks to keep them aligned. Then step-by-step I assembled the crack with 648 lock-tide (strength is 30N per square mm!!). When I had it complete I drilled 3mm holes trough the disks and the crankpins and put in a 3mm pin to prevent the assembly from moving incase the lock-tide would not hold.

I do not have a practical experience yet with this construction, only finished the crank and 4 conrods (about 1 year ago).

Looking forward to see your progress! Regards Jeroen

 

[LongRat]

That's a beautiful method Jeroen, I really hope it works. Seems like the easiest method I have seen for making a complex crankshaft.

 

[pat1967]

Hi Jeroen,

That crank does looks great, would be nice to see some progress on your engine. That design runs in needle bearings doesn't it? I played around with a few different designs too before I decided on the single. Here's what my built up crank would have looked like.

The crank webs are split to allow installing a commercial ball bearing, which eliminates having to harden the "webs". I thought of machining each throw and web halves as one piece, but couldn't work out how to countersink for the bolts, which would be almost equivalent to a solid crank and allow replacement of the bearings if they ever needed it.

Pat

 

[coopertje]

Hi Pat,

Correct, in the original design there are needle bearings. However I find them quite expensive, so mine will be made from bronze. The big advantage is that you can keep them as thin as you like. And I do not plan to run my engine for 100.000km when its finished so I guess bronze will do.

I like your crank design a lot! I think a combination of your design with my mounting method will be perfect. The 3mm pins (to secure the crankpins) will be locked in place by the bearing and you can use the more cheap bearings instead of the needle bearings. I will use the crank I have now for the 6-cylinder, when building the V8 for sure I will use your design (at least if you allow me too).
My 6-cylinder is on hold now, I have some other project running that I want to finish first. I guess I will not be able to restart it within let say one year.

Regards Jeroen