View original topic: 78mm crank and 82mm crank Page: 1, 2  Next
[email protected] Thu Jul 14, 2011 12:06 pm

Does the case have to be machined to install a 78mm or 82 crank? what has to be done in order for it to work? How does a larger crankshaft enlarge the CC of the motor?

baked beetle Thu Jul 14, 2011 12:23 pm

oh boy. Those are 2 good questions.

Questions that someone who has built a motor, should have the answers to.

The case doesn't have to be 'machined' it can be clearanced by hand. Search on that topic.

The last question is the one that scares me :?

mxracer Thu Jul 14, 2011 12:27 pm

I'm a relative noob here too so I'll share some "noob wisdom" with you before you get hammered. Search :)

That being said. Yes the case needs to be machined to create room/clearance for the longer stroke of the crank.

The 78 or 82MM "larger" crank refers to the stroke (up and down) of the rod and piston connected to it. The two factors that make up the displacement (cc's) of the engine are the bore and stroke. Bore is the piston (or cylinder) diameter and stroke is the distance the piston (connected to the crank via the rod) moves in the cylinder.

BTW that is the very high level answer on displacement. Google "calculating displacement" and read on. :D

[email protected] Thu Jul 14, 2011 12:29 pm

HRVW Thu Jul 14, 2011 1:24 pm

:roll: Clearance the case by hand? yep...I can do that with no sweat.

Have some bastard files...a skill saw...pair of tin snips just in case...set of strong chisels...large hammer to use...elect drill with a set of grinding tools.

Why bother with a pro machine shop when I can do it myself and save $$$$.

jsturtlebuggy Thu Jul 14, 2011 2:04 pm

Never used a skill saw.
Die grinder carbide bits,WD40, an sanding rolls is what I have used.
It is time consuming, but worth while if you have more time than money.

[email protected] Thu Jul 14, 2011 2:11 pm

So when you install a stroker crankshaft, you need to install new class B pistons. The longer piston gives you more CC? Im guessing even after reading the aircooled article, the piston is longer along with a longer stroke from the crankshaft?

Quickstraw Thu Jul 14, 2011 2:19 pm

Quote: The longer piston gives you more CC? :?

The longer stroke of the 82mm crank gives you more cc'c

jsturtlebuggy Thu Jul 14, 2011 2:25 pm

Stroker pistons usally have the wrist pin sitting higher in piston.
Meaning it is closer to top of piston and oil ring.
Pistons usally as shorter skirt for clearance.
Remember piston travels further away from center of crankshaft at top of stroke and closer at bottom of stroke.
Also longer connecting rods are use for some applications.
I have no idea how much mechanical knowledge or ability you have.
Building a stroker engine is really not something that you would want to try for your first build.

baked beetle Thu Jul 14, 2011 3:14 pm

Have you built an aircooled engine before or any engine for that matter? If you have that helps.

[email protected] Thu Jul 14, 2011 4:26 pm

I was reading the off road modifications book and in engine performance chapter they said i could use the 85mm pistons and a stroker crank to get a @1800cc motor. i didnt understand how changing the stroke would make more CC, without adding more size to to the combustion chamber. I could see more compression with a stroker crank, its traveling farther. So i would need to get different pistons too, right? So in a stoke motor the pistons arent using the full stroke of the barrel? The barrels dont have to be longer?

I have taken the motor apart with a friend that knew what he was doing, so i observed more then i assembled, dissasamble no problem.

ColtonMelson Thu Jul 14, 2011 4:43 pm

from my understanding you can use up to a 76mm crank (this would make your 1600 into a 1745cc per ) and not have to change pistons. you would have to shim the P&Cs or get different size connection rods, not sure. ask about it you might be able to do this and save some money.

baked beetle Thu Jul 14, 2011 5:01 pm

thanks for answering the question honestly. :P

A stroker motor requires a lot of measuring to accomplish right. You need to measure things you don't even know exist, in a simple breakdown/reassemble.

I think you CAN accomplish it with the help of several people on this forum, but to me, honestly build a stock motor and drive it and deal with those problems, before you spend a lot of money and something goes wrong, then it's all on you.

If you read this forum for 3 months, you would feel a lot more confident. Then build your motor :)

[email protected] Thu Jul 14, 2011 5:12 pm

I have had this bug for 25 years, it was one of my first cars. I kind of think its time to build a lil bigger. Im thinking a 1776 or so, im running 31' tires that require more power. I would like to have two motors, the 1600 thats in it and a bigger one for fun. So i could use a 76mm crankshaft without doing much clearancing? The 88mm slip in pistons too. Im reading, that some people say you can use the same stock connecting rods? I am searching things out too, i appreciate your advice guys. Ive been reading all sorts of stuff on this site for a while, so much to take in.

bsairhead Thu Jul 14, 2011 5:28 pm

Do not use 88mm slip in pistons! 88 machine in's, great. I vote for stock 69 stroke or at most 74 stroke and 90.5 pistons. You will have to have your case opened up for the bigger cylinders but little or no clearance for the 74 stroke.

ColtonMelson Thu Jul 14, 2011 5:29 pm

you might even get lucky and not have to clearance the case for a 76mm Crank. i have heard some talk on here about the smaller cranks dropping right in, depending on the case number, and im sure it is still recommended to check and recheck that you are going to clear everything. i would say that also is a good thing to look into before paying some one for something you didnt need

baked beetle Thu Jul 14, 2011 5:33 pm

Read this thread. The first pic shows notching in the case to clear the rods.

ColtonMelson Thu Jul 14, 2011 5:34 pm

Damn you bsairhead :lol: you beat me to it.. but running the 88s are his choice. Some people gamble some dont.

[email protected] Thu Jul 14, 2011 5:53 pm

I just saw a pair of thick walled 88's for sale on here, slip in i think. Maybe they were machine in 88s, no they said you only had to get heads machined only.
What book would be best for building a bigger Vw motor. Any good book? How much was the bug video?

ColtonMelson Thu Jul 14, 2011 6:07 pm

this is the list that DarthWeber gave me and said to read before i open my case lol

I'd recommend you get the following books and read them before you start taking anything apart:
The VW Bentley Manual
Tom Wilson's How to Rebuild Your VW Engine
John Muir's Idiot Manual
The Bug Me video on engine rebuilding
All of these give you a different slant on rebuilding VW engines but if you take the time to read (watch) what they have to say then I think you'll be much better prepared to tackle a rebuild.

I figure im gonna get 2 maybe 3 of them before i start

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