ShopTalk Forums | Aircooled VW Tech & Restoration Help

Hello

I Have a V code shortblock with the 200 mm. flywheel. and 23 mm diam. wristpin rods. As I want to built a high reving mild displacement type 4 for my standart bug, I was looking into bike engine pistons for use with bored out 93 mm or 94 mm liners. A friend of mine gave me the specs of the Yamaha VL 1500 (twin cylinder aircooled engine.)
The specs sheet for the pistons says;

STANDARD LIMIT
Compression pressure (Automatic de-compression actuated)1 000 – 1 400 kPa (10 – 14 kgf/cm2, 142 – 199 psi) —Compression pressure difference
—
Piston to cylinder clearance 0.02 – 0.03 (0.0008 – 0.0012) 0.120 (0.0047)
Cylinder bore 96.000 – 96.015 (3.7795 – 3.7801) Nicks orScratches
Piston diam. 95.975 – 95.990 (3.7785 – 3.7791)
Measure at 16 mm (0.6 in) from the skirt end. 95.88 (37.7748)
Cylinder distortion — 0.05 (0.002)
Piston ring free end gap 1st T Approx. 13.5 (0.53) 10.8 (0.43)
2nd T Approx. 14.0 (0.55) 11.2 (0.44)
200 kPa 2 kgf/cm2 28 psi

Piston pin bore 23.002 – 23.008 (0.9056 – 0.9058) 23.030 (0.9067)
Piston pin O.D. 22.992 – 23.000 (0.9052 – 0.9055) 22.980 (0.9047)

What do you think? I always read about skirt claerance. Are those pistons specs (on paper at least) suitable for use in a aircooled vw engine. (I will run upright DTM cooling and 40's Dellortos if that matters) I did'nt see the pistons yet. But I'll go and check the wristpin height etc. and other dimensions. I would like to buy and try a set of them if the pricing turns out to be reasonable. What are the key points to look at when inspecting different make pistons for an aircooled type 4 engine? Has anyone here used bike pistons in bored out typ4 Jugs?

Thanks

Yes, I have seen engines with Yamaha pistons in them.

There was one featured in Hot VWs a few years ago.
Our friends across the pond would be more familiar with the engine,
as it came out of GWDs shop.

So, can it be done?
YES.

Now, how to use those 95.3mm Harley pistons I have.........


Don

Just watch the skirt clearances that you use... Bike pistons have a different alloy and expansion rate than most street car pistons on the market...

A freezer, oven, bore gauge and micrometer are your best friends when determining what skirt clearance you will be best with.. Also watch the ring end gaps..

Yea, I will be having Doug's Machine shop over here bore my
cyls for them. IF I had 4 HD cases and rods laying around, I'd make
an 8 cyl T4.... 4565 CC's !!!


Now to make the domes work in the Type 4 head.....



Anyone know a good aluminium head welder?


Don

Dont assume that those pistons would be better than the proven 96mm options for your high reving goals. I have a Yamaha Road Star (I think thats what those are from) and its not high reving at all. Its a long stroke high torque configuration like Harleys and doesnt rev a whole lot higher than the Harley even though it has overhead cams. These are very high torque road cruisers, not at all like the 10,000 rpm crotch rockets! So, keep clear on what you want to accomplish. Are they lighter? stronger? cheeper? better quality? how are they better? Just a suggestion to think about if you havent already.

I would be happy with just some flat top 2.0's in my 71mm stroke 1700 head engine. Mine are dished and are still quick and powerfull but I bet besides the extra power I would get better gas milage. I get what my 1600 T-1 got, about 25mpg, mostly because I can't keep my foot off the pedal.


Joe

I got two sets, 4 P&Cs, for $80.
THAT is how they are better..........


I'm just gonna use them to build an engine to *play with*.


So, I have 4 sets of pistons.

I still have a set of KB 96ers, and the TWO sets of 96mm,
Ford 2.3Ls that I got for $50. Those are perfect for 66mm cranks.....


The KB 96ers are going on the shortblock this weekend.
Then it is on to the dyno for breakin and tuning!

It's redline is 6500.

IT is almost exacting the engine Jake built for the DB&HotVWs article,
just a *nastier* cam! And without Len's heads......


Don

dstar5000 wrote:So, I have 4 sets of pistons.
Don

Flat sixteen would be ever cooler.

dstar5000 wrote: I'd make
an 8 cyl T4.... 4565 CC's !!!

The flat 16 would be like 9.1 liter+.

Here's a Honda piston from the CFR450R. 96mm, 19mm pin, forged, total height under 34mm, and 261g. Oh, and rated to 9000rpm.

Might be cheaper to get some Chevy pistons,and bore the cylinders,
unless those domes are REAL thick.

dstar5000 wrote: Anyone know a good aluminium head welder?


Don

I have been checking on a couple things and if I had a twin plug head,
the combustion event would be a *ring of fire*, racing around the dome.

Pretty amazing to see on my demo, and efficient........

Unfortunately, the numbers show that that design would comcetrate
heat on the outer edge of the piston, not good for ring lands, and
it would also heat the cyl walls more than normal.

I may mock up a ledge around the *dome* to draw more heat to the piston's mass.

We'll see. It's all just numbers and computations right now!


Don

Talking of the ring of fire., I saw a patent published a year or so ago for a combination spark plug and head gasket. The thing was made like a heavyweight printed circuit and had 6 or so spark gaps around the circumference of the cylinder. The electrical connection was a multi-plug on to the edge of the gasket . Haven't heard whether anybody got it to work , but if they did excess advance would mean that pre-ignition events would be well clear of the piston rings where damage is usually done.

Thanks for all the replys.
Jake I'll follow your suggestions concerning the measurements for the expansion rates. The pistons pricing turned out to be 500 bucks for a set of four. 280 is the cost for pistons and 220 for the rings. By the way the pistons are for Suzuki VL 1500. I'll post the pics. as soon as I inspect them. But that's quite an expensive set of pistons for experimenting. I might as well opt for a set of 96 mm KB's.
Thank you all, and I'll report as progress is made.

My KB 96s are 255 per set and we KNOW they drop right in!