Baja Motors -
more than just a VW motor
This is not an article on how to build a motor. I strongly recommend the first-time motor builder make
use of a Guru to show 'em how it's done.
Instead, this is about what it takes to build a baja motor. Not to be confused with the average VW
engine. Reliability is always a factor, but when you're 20 miles into the boonies, it's a matter of survival!
Furthermore, all these magazine articles show turbocharged 2500cc motors in rails. That's real nice, but
few rails are actually daily drivers, and many bajas are. So reality check comes into play.
Here's a quick reference for a lengthy article.
Special Tools Needed
Two factors to consider when deciding which baja motor to build are: power and reliability. Nothing new.
But keep in mind there's no wreckers where you're going, so many of those street motors you read about
aren't the same application. Drag strip motors are real good in the top end, but I doubt they'd be much at
hill-climbing. Turbos, well it's a complicated subject, but the bottom line is that engine life will be
decreased and there's another level of complexity to deal with when you're far away from pavement.
Engine size is determined by the bore and stroke. Again, nothing new. However, the complicating
factors here are the cylinder wall thickness and compression. VW motors in general have to deal with
a lot of heat, which is carried away by the cooling fins and the motor oil. As your motor generates heat,
the cylinders and heads reach tempratures approaching 600 degrees F! Big time! The scientist can
tell you how the coefficient of expansion of various metals causes your cylinders to increase in diameter
by some small amount when at running temprature. So this cylinder heats and cools again and again,
and if it's not strong enough, it eventually weakens, cracks, wears funny, or does other bad things.
A "stroker motor" is a motor with a different crankshaft, so the stroke, or distance the piston travels, is
larger than the stock 69mm. Every intake stroke sucks in more air/fuel mix, and every compression
stroke smashes it a little bit harder than stock. The end result is higher compression. This can be
compensated for by having the head opened up some, or by using shims under the cylinder to increase
the deck height (the space between piston and head). So the increased amount of air/fuel has a
bigger space to get smashed into, and compression is still in a manageable range.
The dilemma here is: More compression makes for bigger bangs, and more power. More
compression generates more heat. How much bang / heat can your motor take? Add in the
complicating factor that high compression motors need some really good fuel to burn clean. Otherwise
there's detonation (fuel ignites at the wrong time) which causes MAJOR heat problems. If your baja's
a daily driver, you probably don't plan on dumping trick fuel into it constantly, and maybe you aren't
even too hip on buying premium gas all the time. I do say, all the time... compression can't be adjusted
without pulling the heads.
Let's hope you have a good Guru working on your motor, and they can determine what's acceptable
for you. If you drive like a maniac all the time, your requirement is stiffer than for someone who drives
like a maniac only periodically. If you're running decent mountain roads, you keep up better speed
and have better cooling than the person bumping over trees and stumps all day. It's hard to nail down.
However, here's some basic facts to help you out.
Cylinder wall thickness: There's some magic numbers in piston size you ought to know about. The
following CC numbers are based on 69mm stroke.
- STOCK 1600 cc: 85.5 mm. Thick walls.
- 1641 cc: 87mm. Thinner walls. That 1.5 mm is taken from the inner cylinder walls of stock-size cylinders.
- 1776 cc: 90.5 mm. Pretty thick walls, again. Requires machining of the case to fit the larger cylinders.
- 1835 cc: 92 mm. Thinnest walls available. Again, 1.5 mm taken from a 90.5 mm sleeve.
- 1915cc: 94 mm. Walls thicker again, but still noticeably thinner than 90.5 mm.
Most motors larger than 1915 cc have stroker cranks on one of these cylinder sizes.
So, the theory goes like this: since I'm in central Arizona, and it often hits 120 degrees in the desert, I
gotta be careful about that motor heat. I've seen several (literally, almost 7) 1835cc motors seize due
to heat factors - big bang, little cylinder wall to transmit that heat away and stand up to the abuse. So
my choices are 1776 or 1915cc. 1915 has thinner cylinder walls than 1776, while it still has a bigger
bang and more heat - still an option, but not the most reliable option.
So, now that you know this info, let me toss out this gem: Appletree Automotive, one of Michigans' reknown VW parts businesses, has granted permission to link to Appletree Automotive's engine calculator tool! Much thanks to the good guys at Appletree. When you're done with the calculator, be sure to check their web page at http://www.appletreeauto.com.
Components needed to build your baja motor
Following is a rough list of what's needed to build a baja motor.
- Good case. Have it align-bored if necessary, and only by a quality shop that will stand by their
work. The dual-oiler case is the only case to take seriously.
- Crank. Counterweighted is nice, for it allows for higher revs without the funny vibrations. 8-dowled
is considered mandatory in some circles.
- Rods. Never re-use old rods, instead invest the $20 into a set of reconditioned rods, at the least!
Better yet, consider a set of "super rods" with reinforcement built in, and balanced for both large-
and small-ends. Remember - a broken rod tends to take out the head, or crank, or both, and is
guaranteed to do hell to your cylinder.
- Pistons. Cast or forged, either is OK for general use - only the turbo-boys and racers really need
to worry about such details.
- Teflon buttons to replace the cheapo little clips provided as Stock VW. These hold your wrist pins'
position in the pistons, and never break since they're not under tension. Again, the only way to go.
- Rings. Total Seal rings are a real plus.
- Cylinders. Most of us buy a set of pistons & cylinders.
- Cam & gear. Stock cam came with the gear attached, while most aftermarket cams have a bolt-on
- Main Bearings. You'll need to have your crank mic'd (measured with a micrometer, that is) to determine how
much milling has been done to it. You'll also want either the old bearings or the case to determine the
align bore measurements.
- Dowel pins for the bearings.
- Cam bearings. Double thrust is the only way to go.
- Rod Bearings.
- Timing gear. The steel one.
- Distributor drive gear. The brassy, swirley one.
- Racer Spacer. That's what they call this spacer - it's considered mandatory in most applications, since
the stock spacer would flatten and die so often.
- Oil pump. Just break down and buy a new heavy-duty, quality oil pump, for this is one item that must
not be allowed to fail! EVER!
- Heads and all accutrements. I'll take this on as a subject in itself.
- Pushrods and pushrod tubes.
- Cylinder spacers.
- Flywheel and flywheel O-ring. I'll include the dowel pins here.
- Main seal.
- Cam plug. A smallish metal cap that mounts into the case and blocks off one end of the cam.
- Form-A-Gasket material. My guru recommends Permatex Aviation. As a matter of fact, my guru
said he wouldn't even touch the damn thing without Permatex Aviation gasket stuff.
- Gasket kit.
Special Tools needed
Above and beyond your usual collection of tools, here's some specialty items for building VW motors.
Most of 'em you can't build without.
- Deck height tool. When the case is machined, it's often necessary to resurface the cylinder seating
areas. Thus, the cylinder sits a little lower on the case. The stroke is the same, so the piston goes a
little higher towards the heads. You Have To Know this measurement, deck height, to compute
compression. The deck height tool bolts on in place of a head, and has an adjuster & access cutout so
you can measure this critical distance.
- Crank end play measuring tool. This is not a complicated thing - a tool that bolts into one of the
engine mounting holes & allows you to measure the distance the crank moves from end to end. Hot
VW's magazine says the proper crank end play is .004 to .006, while the good guys at Karl's Custom
say it's .005 to .007. My point is, when working with such tiny increments, a good tool is required! All it
does is allow a solid zero-point when the crank is forward, and a good measure when the crank is
rearward, but I don't know how to mickey-mouse anything solid enough to distinguish a few thousandths.
- Main seal seating tool. The main seal is a big guy - maybe 5" in diameter. This tool has a big flat
dish & a bolt that threads into the end of the crank, and presses the main seal in evenly. This could be
mickeymoused, but this $10 tool could save you a lot of trouble!
OK, now that the basic list is assembled, let's talk about some of the trick stuff.
- Bore Align: this isn't really trick, it's standard. The cases get worn where the main bearings sit. These
marks need to be machined for proper round, depth, etc. They sell oversize bearings for just this
reason. Any bunk you've read about bore-aligning weaking the case or causing heat problems
makes no sense to this Lizrd!
- Sand Seal : The sand seal compensates for the stock VW way of having no rear seal whatsoever
in the motor. Instead, the pulley has these swirley shapes to pull the oil back in. If you play in the sand,
the pulley pulls in the sand, too. Enter the sand seal, which fits into a specially machined socket in the
case, and requires a different pulley. This is a good thing, but it's also one more thing to fail and make
your motor spit oil all over the place. Not to mention, funny things are known to happen with sand seals,
such as pulling a bad seal & cracking the case.
- Welded 3rd cylinder back: The studs for cylinder #3 have the least depth of all the studs in the case.
So, under extreme cylinder pressures the back of the case may crack. I was told that with compression
in the pump-gas acceptable range, a mild motor and common sense, this rather-expensive modification
is not necessary - and I believe it.
- Full-circle crank: This crank is counterweighted with gusto. Helps remove vibration and improve
motor life. However it's heavier, so harder to spin up, and much more expensive. I've never had one.
- Lightened Flywheel: This could be a big deal. The stock VW flywheel is in the neighborhood of 16
lbs in weight. a 12-lb flywheel will be much easier to spin up. But, when launching your big baja tires
from a standstill, you need that extra angular momentum to keep your motor spinning until you can
make power again. Thus, if your gearing is too tall, a lightened flywheel may be a bad idea.
- 8-doweled crank & flywheel: The flywheel sits on the crank by these little dowel pins, maybe 1/4"
in diameter. Stock cranks have 4. Big motors break 4 dowel pins regularly. So 8 dowel pins are better!
- Full-Flow case: This modification machines into the oil galleys near the oil pump & adds fittings for an
external oil filter. Considering that the stock VW motor has no filter at all (only a screen), there's nothing
wrong with this. But do remember, it's one more place to get slammed by rocks and leak all your oil out.
I chose to go with an external oil filter / cooler combination, which has a fitting to replace the stock oil
cooler & provides two fittings for 5/8" oil line. The output goes to the filter, then to the cooler, then back
to the motor. So the filter is up on the body of my baja and far away from rocks. Some say that the stock
doghouse oil cooler is the best cooling solution ever made, while Bugpak said this external cooler is
better. I'm not sure who to believe, but I do know that they both work!
- Oil-groove pistons: European Automotive offers this neat trick: cut a few minor grooves around the
skirt of the pistons below the wrist pins. This helps retain some oil in the cylinder, and helps cooling and
decreases wear. Sounds great, huh?! At the major cost of $5 a piston, it's a steal!
VW cylinder heads are an arcane science all of their own. You can spend several hundred dollars on
heads alone, and I'm sure they're worth it, but what do you really need for a baja?
All I can suggest is that you talk to several head experts. Some will say that flow is paramount - thus,
bigger valves, ported so much that they need to weld in some areas for strength to compensate, would
be their answer. Others say that big valves reduce low-end torque and response, since the swirl of
incoming charge is critical at lower intake velocities. Some say that VW spent a fortune on head
engineering, but no one says that Gene Berg was wrong. One baja fanatic tells the story of the
big-valve heads he put on his 1776cc baja motor, then swapped out for stock heads
he'd purchased for his wife's VW. Make Up Your Own Mind.
Some general info is globally accepted, however.
Heavy-duty valve springs are good, since stock valves can skip at 5000 rpm. Dual valve springs can
cause excessive wear and clearance problems, so probably aren't for the average baja motor.
- Stainless steel valves just last longer. They dissipate heat better, don't stretch as readily, and are
recommended for all exhaust valves.
- Chromemoly valve keepers are possibly excessive, but if you ever broke a keeper, it's possible that
your valve would fall into the cylinder, impact the piston at speed, and break many hard parts causing
a great wailing and gnashing of teeth. A good investment, viewed this way.
- A mild port job can't hurt. Fashion has changed from "polish to a mirror finish" to leaving it rough enough
so droplets of raw fuel don't just run down the surface. Instead, any droplets of raw fuel have a chance
to evaporate in the airflow and become useful again.
- a mild "open-up" job on the head is almost mandatory. Stock heads shroud the valves excessively,
so 5 cc of openup means a lot. European Automotive, the shop I took my heads to, do this as a matter
- And finally, heads are bloody critical. Valve job / inspection is relatively inexpensive - European
Automotive quotes a price slightly over $100, saying that the average head needs a couple of valves,
valve guides replaced, maybe replacement of a weak spring or two and the average price reflects this.
You'd be an idiot to rebuild a motor without investing in a little head work.
As always, this SandLizrd knows there's more to be said!