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Tue Dec 09, 2014 10:36 pm

Does anyone make regular length 94mm cylinders or should I say same length as others sizes?

Tue Dec 09, 2014 11:29 pm

They're a little longer to give more deck height, so your compression isn't too high. If you want shorter 94mm cylinders, just send them to the machine shop to get turned down. Simple.

Wed Dec 10, 2014 8:31 am

or machine the case...

Wed Dec 10, 2014 11:55 am

modify the cheaper part.....the cylinder.

Wed Dec 10, 2014 12:27 pm

I have to get the case decked which will take the extra length off but I still need another .06 off. I don't want to go too deep on the case. It would be perfect if they made the regular length and I didn't have to get both sides machined.

Wed Dec 10, 2014 12:50 pm

jason wrote: I have to get the case decked which will take the extra length off but I still need another .06 off. I don't want to go too deep on the case. It would be perfect if they made the regular length and I didn't have to get both sides machined. i had the same issue so we cut the cyclinders down .60 i believe . dont cut the case

Wed Dec 10, 2014 1:06 pm

The solution is obviously a bigger crankshaft.....

4mm more stroke should fix it!

:twisted:

Wed Dec 10, 2014 8:10 pm

[email protected] wrote: The solution is obviously a bigger crankshaft.....

4mm more stroke should fix it!

:twisted:

I really like Johns idea!!!! Don't forget that the wrist pin distance is also different, Mahle 94 = 35mm Mahle 92 = 34mm

Wed Dec 10, 2014 8:35 pm

Thing_Man73 wrote: [email protected] wrote: The solution is obviously a bigger crankshaft.....

4mm more stroke should fix it!

:twisted:

I really like Johns idea!!!! Don't forget that the wrist pin distance is also different, Mahle 94 = 35mm Mahle 92 = 34mm if u have the cash for the crank go for it.

Thu Dec 11, 2014 7:38 pm

I'm not going to try and stuff a 90mm crank in there. I'm going to use C pistons so I don't have to use 1/4" spacers. Spacers would be cheaper than all the maching but I'd rather keep it as narrow as possible.

Thu Dec 11, 2014 8:06 pm

then it's obvious you have an assortment of mismatched parts. You either need more crank, or a longer rod. If you are too committed to keeping parts you have already, that were chosen prior to having a good plan, THAT
is your problem.

You can use longer cylinders, but those always require machining to make them the actual length needed, as it differs for each engine.

jason wrote: I'm not going to try and stuff a 90mm crank in there. I'm going to use C pistons so I don't have to use 1/4" spacers. Spacers would be cheaper than all the maching but I'd rather keep it as narrow as possible.

Thu Dec 11, 2014 8:35 pm

[email protected] wrote: then it's obvious you have an assortment of mismatched parts. You either need more crank, or a longer rod. If you are too committed to keeping parts you have already, that were chosen prior to having a good plan, THAT
is your problem.

You can use longer cylinders, but those always require machining to make them the actual length needed, as it differs for each engine.

jason wrote: I'm not going to try and stuff a 90mm crank in there. I'm going to use C pistons so I don't have to use 1/4" spacers. Spacers would be cheaper than all the maching but I'd rather keep it as narrow as possible.

I am kind of with John, if you are committed to keeping parts you have already don't ask for advise, just do what YOU think is best for you.

Thu Dec 11, 2014 10:19 pm

The 86mm Berg crank and 5.5 carrillo rods are nice parts, and I can understand wanting to keep and use them. For sure, having some cylinders cut down is going to be the cheapest option. You might also look at trimming the top of some B pistons, and using a smaller shim.

Fri Dec 12, 2014 9:25 am

For a moment there, I thought the OP asked "whether stock-length 94mm cylinders exist" and he was answered with "buy a longer crank or longer rods".

:roll:

Jason, as a few others have correctly suggested, cutting the cylinders to length is the best -and most cost effective- solution. FWIW, don't rely on your back-of-the-napkin calculations. Have your case decked, procure the parts, then mock up the assembly with uncut cylinders to determine exactly how how far down to have the cylinders turned. You can account for any cylinder shims or head gaskets at that time, too (if you have any inclination in playing around with deck-height and CR in the future...).

Fri Dec 12, 2014 9:37 am

I would simply mock up the engine, and see how much stuff needs to move. A lot of guys think you can just do some maths and figure it out, but the reality is a lot different.

Just get off your ass and mock it up, and then the best solution is obvious.

It's normal to deck the case .060" when boring for 94s for a nice wide surface for the cylinder base, which makes the net change 0 when used with the longer 94mm cylinder.

As an aside, the main problem with stock length cylinders on long stroke engines is not the top, it's the piston pulling out of the bottom excessively. I've seen some guys that step bored the case and used the case as the piston support at the bottom, since the piston slid down/out of the cylinder so much. A good machinist can handle this, but you have to be paying close attention to stuff. I've never done this BTW.

Fri Dec 12, 2014 10:22 am

I know I have to mock it up but I haven't bought the pistons yet. I was wondering if they made the shorter cylinders so I could figure out which way to go, B or C pistons. I wan't to buy super squishy pistons so taking some off the top isn't going to happen. When cylinders are shortened do they take some off the ends or only on the seat?

Fri Dec 12, 2014 11:30 am

Quote: When cylinders are shortened do they take some off the ends or only on the seat?
Both. I know you are trying to plan everything out and not have to send stuff back to get machined but sometimes you cant help it. Take john's advice and know that every situation ( build) yields slightly different results. Know that he will give you the best advice to get you close. And also, know that you may have to use shims. IMO I would get the normal length cylinders and just add shims and or gaskets if need be. Sending cylinders are cheapest. Since in all likely hood its going to stick out. Getting the heads compression flycut on the cc's is the last youll have done.

Fri Dec 12, 2014 11:44 am

one trick is to use normal cylinders built to "zero deck", and then use copper head gaskets at the top for the final DH. This effectively makes the cylinder longer. I knew some guys that would run a .090" head gasket, and run the piston up around .050" into the gasket, for a final deck of .040".

When choosing between $30 head gaskets and $250 cylinders AND machine work, sometimes it's an economical option.

With your engine, you are 86mm and 5.5"? This is ~.180" out more than stock per side. But that's "more than stock", in actuality it will be smaller, because you will build a tighter deck anyways. I recall the 86/5.5" is a Berg combo that is designed to use stock cylinders with Bs. It's not that much wider, certainly reasonable at around .180"/side. And like I mentioned, actual shimmage will likely be less when it's assembled.

If it were me I'd assemble with an old Cima B, and measure where it's at for reference. Then you can do your final calculation on the napkin and it's useful, instead of 100% napkin theory.

Also, FYI squishy Cs are 1.055, and Bs are 1.380". So you can see how C's are going to create as many problems as you are fixing, with your in-between combo. If you switch to 5.7 rods it's a no-brainer, but not with 5.5s.