TheSamba.com :: View topic - 5.4" H-beam rods with 78.4 crank?

Tue Mar 19, 2013 8:27 pm

My build plan changed due to my newly acquired 82mm crank being no good. This week I stumbled upon a really sweet old school SCS(small car specialties) 78.4 crank wedgemated to a lightened flywheel. I had already purchased a set of 5.4" h-beams as it was recommended for the 82 stroke. Tonight i emailed John at ACN and he informed me that the 5.4s can make the assembly more difficult such as to much deck at TDC. So.......how many of you have built engines with 78/78.4 cranks and 5.4" rods?? What if any problems did you run into??
I am building a 2085cc. 92x78.4, 120cam and 1.25 rockers. 52cc custom hand ported heads with 40/35 valves. Dual weber 40idfs. Want Cr to be somewhere in the neighborhood of 8.7-9.3. With my heads at 52 the deck needs to be in the range of around .070. Am i going to run into alot of fitment problems or should i just bite the bullet and get a set of 5.5" rods?? Id sure hate to spend another $230+ on more rods. Arghhh!!!!

Tue Mar 19, 2013 8:33 pm

mock it up and see where you are at. For this put the calculator away.

Tue Mar 19, 2013 8:34 pm

I would think that the rods would work for the 78.4 if they were originally going to go on an 82 crank. I would not want that cam though.

Tue Mar 19, 2013 8:39 pm

I assume you are running "A" pistons??

Tue Mar 19, 2013 8:56 pm

MURZI wrote: I assume you are running "A" pistons??

Thickwall AA 92mm stroker pistons.

Tue Mar 19, 2013 8:58 pm

Yes, as mentioned in your OP, when you build an engine with a 78.4 mm crank with 5.4" rods and Mahle B pistons, using an OEM case, you can end up with 0.100" DH (or more). Some will elect to trim the cylinders, deck the case, etc, however, I chose to sell my 5.4 rods and replace with 5.5's.

Tue Mar 19, 2013 8:58 pm

[email protected] wrote: mock it up and see where you are at. For this put the calculator away.

Yea i know. I just dont like doing things multipl times.

Tue Mar 19, 2013 9:00 pm

So are they A pistons or B's?? Do you know?? Have you mocked up anything yet? One rod, piston, cylinder??.

Tue Mar 19, 2013 9:03 pm

neil68 wrote: Yes, as mentioned in your OP, when you build an engine with a 78.4 mm crank with 5.4" rods and Mahle B pistons, using an OEM case, you can end up with 0.100" DH (or more). Some will elect to trim the cylinders, deck the case, etc, however, I chose to sell my 5.4 rods and replace with 5.5's.

Not what im wanting to hear. My case is being machined now for the bore and stroke. Really dont wabt to have to ship it back to have it decked if need be. Sounds like trimming the cylinders will be my easieat route unless i find someone else who bought the wrong rods like i did.

Tue Mar 19, 2013 9:05 pm

You might get lucky, as sometimes the machine shop will deck the case to fix the problem of inserts sticking up too far...so this might bring your DH down a bit.

Tue Mar 19, 2013 9:07 pm

Why not buy a 82mm crank instead..... About the same exact cost....

Tue Mar 19, 2013 9:11 pm

MURZI wrote: So are they A pistons or B's?? Do you know?? Have you mocked up anything yet? One rod, piston, cylinder??.

They are B's for 82mm crank.

Tue Mar 19, 2013 9:16 pm

MURZI wrote: Why not buy a 82mm crank instead..... About the same exact cost....

My OP stated that my 82mm crank was no good. It had a crack between dowel pins. I ran into this 78.4 crank/flywheel (wedgemated) combo and purchased it for $350. My plan was a 2180 but the crank issue changed that and i couldnt walk away from this old school crank. Besides i think at 2085 will be a better match for my 40idfs anyways.

Tue Mar 19, 2013 9:20 pm

Great build up of a 2085. Mightymouse did a very detailed write up. I've read that thread a few too many times.

http://www.thesamba.com/vw/forum/viewtopic.php?t=444148&highlight=stroker+camshaft

He used 5.5's.

Tue Mar 19, 2013 9:21 pm

even fixing the problem with cylinder machining, you can wind up with additional unexpected issues from this "solution", depending on how much you have to do.

PRs are too long
Cylinder tin doesn't fit right
intakes hit the tin (tin stock location, heads "in")
Exhaust is now too wide

This is a huge problem not talked about when people deviate from normal engine widths, both narrower and wider. The only thing easier with a narrow engine is it fits into the engine bay easier, but the rest of the issues can still bite you.

Tue Mar 19, 2013 9:22 pm

mrblyoung wrote: Great build up of a 2085. Mightymouse did a very detailed write up. I've read that thread a few too many times.

http://www.thesamba.com/vw/forum/viewtopic.php?t=444148&highlight=stroker+camshaft

He used 5.5's.

I too have read it a few times. He did an excellent job. Wish it had more info on the performance of the motor such as dyno numbers. I would like to somewhat replicate his build.

Tue Mar 19, 2013 9:31 pm

[email protected] wrote: even fixing the problem with cylinder machining, you can wind up with additional unexpected issues from this "solution", depending on how much you have to do.

PRs are too long
Cylinder tin doesn't fit right
intakes hit the tin (tin stock location, heads "in")
Exhaust is now too wide

This is a huge problem not talked about when people deviate from normal engine widths, both narrower and wider. The only thing easier with a narrow engine is it fits into the engine bay easier, but the rest of the issues can still bite you.

Dang it John!!!! Want to make me feel better and trade mr some 5.5s for my 5.4s??? ;-)

Tue Mar 19, 2013 9:38 pm

pigzsnout wrote: mrblyoung wrote: Great build up of a 2085. Mightymouse did a very detailed write up. I've read that thread a few too many times.

http://www.thesamba.com/vw/forum/viewtopic.php?t=444148&highlight=stroker+camshaft

He used 5.5's.

I too have read it a few times. He did an excellent job. Wish it had more info on the performance of the motor such as dyno numbers. I would like to somewhat replicate his build.

Agreed. Dyno info would be cool, but not all owners care about exactly what their motor is making. Can't blame the owner though. mightymouse built a stout motor and the owner is obviously very happy with it.

I'm planning on building one somewhat similar, but I'm building a 76x92 instead of the 78.4. Very similar though.

Tue Mar 19, 2013 9:59 pm

pigzsnout wrote: MURZI wrote: So are they A pistons or B's?? Do you know?? Have you mocked up anything yet? One rod, piston, cylinder??.

They are B's for 82mm crank.

That means nothing in particular to me.

The cylinder lengths can be 112.5 or 114mm
the pin height can be 34-35mm, yours are probably 34.9mm

depending on if the case was cut for 94's it may be surfaced 1.5mm, or it may not, or maybe your using the newer AA cylinders that fit a 96mm case hole? I don't know the length of those

You tell me bro, we have no way to know

Tue Mar 19, 2013 10:39 pm

push rods are easy fix, new set.I have the 5.4 with the 78.8 scat crank, I just cut the cylinders down.(or rather cut them up, from the lower portion that contacts the case,did some other mods too but we wont go into that as yours wont need that done)but you need to mock it up to see exzactly what it will need. and dont forget, head gasket or not???step in heads or not, etc