Stroking a 1500 crankshaft questions.

Has anyone stroked their crankshaft by off-center grinding their connecting rod journals? C. Obert has .050" and .060" undersize con-rod bearings...this in theory could give your engine another 2-2.5mm of stroke!

Can the crank gound undersize like this remain reliable?

I havent' done it, but I'd think so...


When I first grabbed the Fiat "Haynes' manual that came with the X1/9 I bought, I was glancing at rod bearing sizes... the silly gearhead in me got to thinking...

I think there are some older Honda's that had stock 42mm crank size, and a 45mm external size to fit in the rod... you'd have to have custom rods made... But you could offset grind the SOHC crank down quite a bit with those lil suckers. And if you had the crank welded up on the outside of the stroke before you offset ground it.. Whoo hoo!

I don't think the old Honda CVCC motors were famous for breaking cranks... and the sohc cranks are pretty stout right? Even cut down they'd probably be ok. The problem (this is off the cuff) is the Fiat bore is quite a bit bigger... so the piston is going to possibly be heavier... at RPM... the smaller bearing diameter/size might be a problem. I'm definitely not schooled enough in engine 'design' to have a clue.

This is all bench racing day dreaming... by the time you did all that you could probably stuff a RSX type S engine and tranny up there and be going even quicker.

The other problem...

With stroking an engine by a bunch is that you run out of room at both ends of the bore.

At the top, you don't want the piston popping out the top of the bore. The usual solutions to this are to change the piston compression height or shorten the rod. Changing the compression height involves moving the rod pin bore up the piston. But pretty soon you are into the ring lands. Shorter rods tend to accelerate engine wear.

So let's say you have stroked your crank by 3mm. If you were able to move the pin bore up by 3mm, problem solved. But if you could only move it up by 1mm, then the other 2mm of stroke, plus the 3mm, will mean the piston pops out the bottom of the bore by 5mm. Even if you completely addressed the problem upstairs, the piston is still going to travel 3mm further down the bore than stock.

This can cause problems in several ways. First, the piston may come so far out of the bore that it can cock in the bore. Catastrophic engine failure will follow in microseconds. Second, when the piston is at the bottom, the counterweights are at the top. This brings the piston skirt very close to the counterweights. A shorter rod (see top-end discussion above) will exacerbate this. Third, the increased swing of the rotating mass may contact the block at the rod bolt and oil pan skirt.

Lots to consider throughout the engine before you can successfully build a stroker.

Still, Ron's (Abarth2.0L) engine weighs in at 1800cc, so it can be done.

Pete

Why?...

You can pick up 3.5mm stroke by replacing the crank and pistons with stock parts. This gives you 1581cc

High performance can be served by going to SCAT rods and forged pistons in your choice of bore size.

Charlie's post lists a well developed program at 1650cc

Ron Gallo's 1800cc motor represents close to the ultimate obtainable in a single cam motor

The costs represented rise in an exponential curve. So, choose your $$$ figure you want to pursue.

Ciao,

Answers...

I have seen the 1581cc conversion with stock parts...But where in the world can you find these parts in the USA? Even if you could find them they would probably be outrageous.

1600cc stroker cranks are high $$ too. The same goes for SCAT rods. That's why I was wanting to stick to offset ground rod journals.

I understand the poping out of the bore problems...but heck...Mad Matt sells high performance pistons that reach into the counterbored area on stock heads. I believe this is a moot point...surely this can be overcome even if it means machining some material from the top of the pistons.

Do you really think .050" more at the bottom of the stroke will lock up the piston in the bore?? I have to believe this cannot happen with .050" more stroke at the bottom. The conecting rod angle at the very bottom of the stroke is 0 degrees and as soon as the crank swings over just a few degrees...the piston start heading up the bore again.

If rods come closer to the cylinder skirt...just notch them with a die grinder until they clear. I have seen this done on Datsun 510's with great success. If the piston skirt comes in contact with the crankshaft...have the machine shop turn some off the O.D of the counter weights. Lightening the crank will probably be necessary anyhow. After all, sanding and polishing of the con-rods along with bead blasting afterwards should probably be done if stock rods are to be reused. If SCAT rods are used....they will be lighter than the factory rods to begin with.

I am a big fan of machining the rods the way Cosa Mesa R&D does it. For a daily driver his methods of lightening the rods looks great.

Bigger pistons may indeed be heavier. But there are several ways to loose the weight. Most involve a milling machine and some careful cutting with an end mill. Most shops could probably doo this too. Custom oversize pistons like the ones Mad Matt offer...are usually lighter than stock too. I am going to find something cheeper that $700 !!

My biggest concern would be weakening the crank. Does anyone have history with undersizes rod journals??? And do they last?

My commentary was not specific to the SOHC motor...

etownsley said:

Do you really think .050" more at the bottom of the stroke will lock up the piston in the bore?? I have to believe this cannot happen with .050" more stroke at the bottom. The conecting rod angle at the very bottom of the stroke is 0 degrees and as soon as the crank swings over just a few degrees...the piston start heading up the bore again.

Click to expand...

And as I referenced with Ron's motor, some heavy stroking is obviously possible.

My point was more along the lines of things that will need to be considered. I have never stroked a SOHC motor, so I'm not sure what the pitfalls are. Just trying to offer some information. I have no idea what your level of engine building experience is.

Pete

Hello!

I´m new to this forum! Found your website after searching for stroker kits!

There are 2 ways to stroke the 8v: 1840cc or 2100cc ! Last version is with block extention plate to have 2100cc.

For my 1.9L Turboproject i use this pistons with conrods in stock length and a 78.4mm crankshaft!



If anyone is interested in more pics let me know!

Btw. great forum with huge knowledge!!

Best regards
Keule

Mark Plaia said:

You can pick up 3.5mm stroke by replacing the crank and pistons with stock parts. This gives you 1581cc

Click to expand...

Mark:

For the search impared, please detail.

Grazie

Welcome Keule...

Show us, tell us more!

I'm not gonna lie to ya and say I'm gonna do any of this... but your numbers are BIGGER than any others I've seen or heard of before on this site.

We'd love to see photos of your ride as well.

Hello!

My car is not x 1 9, thats first But i really like the old 8v engine and spend lot of time and work to build a good 1.9L FWD with arround 320hp to 350hp!

Only to show some things....
Custom made 215mm flywheel with paddle clutch ready for 500nm of torque




Tubular Manifold


Big Valve Head


Custom made Downpipe


Work on the Block to fit the 78.4mm crank ( 1500 Closed Deck )




We have here a ready 1.9l running. 310HP at 1.2bar. 400NM Torque
Revs easy to 8000rpm. My build see a little bit more rpm!


Hope you like it! I made a lot more. If anyone need more informations! No problem ....and sorry for my bad english

Feel free to elaborate on what we're all drooling over!!! Please!

Kevin, 67.4 mm cranks are available...

They are available in Europe, and imported to the US. Check in with C. Obert & Co. for local availability.

Ciao,

Yes, thats true! But with the 67.4mm crank you only come to 1.6L. With the 78.4mm crank you see 1840cc. With the 90mm crank 2100cc.

Great stuff

Kuele this is really great. It looks like you are using a 1500 block. I guess it is not the Tipo block. It also looks like you removed some of the oil gallery. Is there enough meat left on the oil gallery to still be functional or does your motor need external oil pluming?
Thanks
Charlie

All works fine! There are some tricky ways to grind the material! But no problem till now! First engine run over 4000km without problems! Next step is 1.5bar and hoping to see 350hp+

Btw. i found a tread about another Stroker. Costs were 15000USD. Is this a joke?

Intriguing. Where are you getting these long stroke cranks?

This is all very interesting but...

Does anyone have experiance with offset grinding the connecting rod journals? The stroker kits that are all mentioned here can be done with $$$. I want to hear from someone who has done it the cheap way and gained a little more torque and hoursepower but also retained stock reliability.

Not sure here if anyone has tried offset grinding to stroke their motor... but I would think that unless you operate your own machine shop, buying the 67.4 crank for a few hundred bucks would be the cheap way...

or is machine work just way expensive in my neck of the woods?

Full N/A Kit




and fitted on 1500 Block




I know some guys who run this engine with throttle bodies from suzuki gsx 1000r (42mm) and make with standalone management 220hp.

Regards
Keule

Very nice, but where did you get the long stroke cranks from? 78.4 from the Marea 16V engine? 90 from ?