KB's in a 318 with No Re-balance

[dartfreak75]

I recall a 360 build by some magazine. It was some time ago. They used the KB107'S and did not balance rotating assembly. It was a cheap type build. They ran car to get some times after break was done. And claimed that engine ran surprisingly smooth @ all rpm's.

This is something i have been curious about. Kinda what got the whole process started. Me and nm9stheham was talking about budget builds and how necessary rebalancing was if it was just a low performance, low rpm street car. Obviously in a race car where your turning high rpms constantly its gonna be crucial that everything is done precisely. But in low performance builds where is good enough? So he started plotting out some homemade balance stuff and this is what he came up with. I think its great. Nm9stheham did a great job with this!

 

[1778ppr]

I know this thread is more than a year old.
I have been thinking about doing this for a long time. Has this "pin balance sleeve" been tried? How did it work out in a running 318? Give us an update. Thanks for posting all this. John

 

[nm9stheham]

I only made the 1 for initial testing. So not tried in a real engine. It's one of the many builds on my radar, many of which I will never get the time to do.

I can see the fears some will have over this; you have to look at the temp of the pins and the release temps of the sleeve retaining compound. Pins don't get above 300-350F even under extended heavy loading, and that is only at the ends; the central area stays cooler. You can do the research and find this info. The compound releases at 450F or higher. This is the same compound used to seal in cylinder sleeves, so it is a known working item.

If you can find some good condition 273 wrist pins, then that is the other way to do it. The 273 pins were made heavier on purpose to balance with the lighter 273 pistons, on the the same crank as the heavier 318LA pistons.

 

[1778ppr]

What about the pin retainer clips? Wouldn't that keep it from interfering with the cylinder wall? I can't find a good pic of the KB167 pin clip design.

My original thought was to make the "balance pin" out of aluminum rod installed with a light press fit. Size on size. If it did move it would only be aluminum not steel rubbing on a lubricated cylinder wall. My biggest worry about that was expansion rates between the aluminum pin and steel pin. I'll have to do more research.

When I found this post I was glad to see someone else thinking the same. Also why don't they just make pins for this? It seems like this is a no brainer to me. The same situation for BB400. Which is why I frist considered this. Now I'm looking to build a cheap 318 for my truck. If Silvolite made a 318 flat top cast piston OEM weight with 1.810" compression height for a comparable cost to the stock replacements, they would have trouble keeping up with the demand. We're only talking 318 power here. 350 hp maybe. Most builds probably won't see that.

 

[nm9stheham]

I actually wrote KB and asked if they could make a heavier pin or a heavier piston. Never thought about a taller cast piston. They said they would consider it. But I never expected it to happen... and I have not been dissappointed LOL.

IDK if you could get the needed weight with an AL insert; you need to end up in the 210 gram range IIRC. And the expansion difference would seem to be an issue. But, some Formula 1 engine builders used a hybrid AL/steel pin for a while, so it is not a new idea and has been used in a high stress application. I'd personally rather stick with the same materials and keep the lengths equal so the pin flexing does not have any discontinuities. And I don't think you can count on the locks, at least in their common forms.

Speaking of which, pin flexing and the effect on the retaining compound is a thought.... These compounds get used regularly to put bearing repair sleeves in machinery systems so they work with some level of vibration, etc.