Could anybody help me with putting together 78x90,5?

[Bruce2]

H beam rods are getting pretty cheap and are a great improvement over stock rods

In the OP's engine, replacing the stock rods gains nothing. The stock rods will be indestructible, and they're free. Remember, the OP is on a tight budget.
Back in the olden days, before cheap China rods were available, drag racers used stock or stock modified rods. I've known guys who ran stock rods over 9000 rpm, and in turbo motors making well over 350hp with no problems.

I agree with you on the oil windage plate. The only thing it does is prevent oil from getting back to the oil pickup quickly.

[V8Nate]

Thanks for your answers.

vhat about rods, they seem to be grinded stock ones but bolt head look really weak....yep they didn´t broke down but looks really weak. Maybe some other rods fit better without grinding them

That's why I suggested rods, they can also aid in clearance on the big end.

[Bruce2]

I'm surprised no one noticed that the case has not been clearanced!

Normally, the case is clearanced some, and the rods a bit more. In the above engine, all of the clearancing was done to the rods.

My recommendation is to clearance the case, then get another set of stock 1600 rods and clearance them, but not as much as was done in the dead engine.

[joosep]

Thanks for your helpful answers

[GowpenfulJ]

Don't know much about engines but you'll surely get some help from here ..
Good luck ..

[joosep]

Finally my friend decided to order some parts and start working with that engine.
Im quite sure we do as it was... 78x90 (because its cheaper and easier) but I have to ask....
What I noticed is that 82 cranks are easyer to find or sometimes cheaper than 78 What would be te main things I have to deal when we go big. conrods should be the first and major problem I see.... Is there anything useable between cb performance H profile and stock ones (I mean price)
I´ve read about pushrods lenght, tin problems etc, what else would fight against me ?
Thanks

[FJCamper]

Hi Joosep,

I'm just mentioning all this in general. This is guidance, not rules. There are exceptions to everything.

I'm presuming you're making a street engine, bus engine, sedan engine., etc. We build race engines for sedans and Ghias, but have of course built many street engines.

You're specifying 90mm pistons. There was once a time (long gone) that 94mm pistons and cylinders had a bad reputation for reliability because the early 94's were thin-wall cylinders. Today, you get the same wall thickness on a 94mm as an 85.5mm. So, if you were going for a 90mm thinking you were preventing cylinder warping, that's not an issue any more.

We've discovered a "sweet spot" in our endurance racing engines of 94 bore by 78 stroke. Power and reliability. That's 14 hours of flat out full throttle racing per weekend.

Longer strokes really place extra stress on stock VW AS41 magnesium cases. I saw an 84 stroke crack a whole case roof right off at an endurance race. Now maybe if you're building a long-stroke street engine and you can keep the RPM's down, this won't happen to you, but the rule is if you build in extra power you will use it.

You also mentioned con rods. If you are stroking beyond 74mm, use H-beam rods. The cheaper chromoly I-beams are plenty strong for 69mm to 74mm strokes, but not for heavy piston, long stroke, high RPM engines.


FJC

[Bruce2]

You're specifying 90mm pistons. There was once a time (long gone) that 94mm pistons and cylinders had a bad reputation for reliability because the early 94's were thin-wall cylinders. Today, you get the same wall thickness on a 94mm as an 85.5mm. So, if you were going for a 90mm thinking you were preventing cylinder warping, that's not an issue any more.

I think you're confusing 94s with the new 92s. The problem with 94s is still the same, nothing has changed in the dimensions of 94s, they are still thin at the top where they meet the head.
The old 92s used to be the same OD as 90.5 cylinders at the head. Then when AA came around, they made their 92s using the same cylinders as 94s but with smaller IDs resulting in thicker walls than either 94s or 90.5s.
In theory, the new 92s should live longer than 90.5s, however I have never heard any high mileage claims from users of the new 92s. Reports of 90.5s living over 100k miles are easy to find. I have one such set in my car right now.
Anyone here got a set of 92s with over 100k miles on them?

You also mentioned con rods. If you are stroking beyond 74mm, use H-beam rods. The cheaper chromoly I-beams are plenty strong for 69mm to 74mm strokes, but not for heavy piston, long stroke, high RPM engines.

I agree that stroke, piston weight, and RPMs are what matter when choosing a rod.
If the OP stays with 90.5 pistons, they weigh significantly less than a 94 piston, especially if they use a AA slipper skirt piston instead of a Cima full circle piston. In that case, stock rods are more than anyone needs for a 78 stroke engine.

[FJCamper]

Hi Bruce,

I believed that "modern" 94mm cylinders had that initial thin-wall problem solved because of ads I read some years later (CB Performance for one?) claiming 94's were now safe. I never cut any cylinders to measure actual thickness for a reason -- complaints about 94's dropped off so much as to be insignificant.

Being no expert in cast iron, I had heard from reliable sources that there were poor castings and inferior metallurgy in some cylinder products compared to others. Certain iron alloys were too brittle, some too soft. I did learn that you should tap a bare cylinder with a steel wrench or hammer and if had the right metallurgy, it should ring like a bell. Too soft, and all you get is a clunk.

There must be some balance in casting a rigid cylinder (high precision) which is on the verge of brittle, to casting a softer cylinder that lives through heat expansion and cool-off contractions better.

My rule of thumb in all things related to cylinders is Porsche's original biral cylinders used on the mid-1950's Super engines. We even run aluminum Nikkies on one of our race cars. But, Porsche dropped the birals and went back to cast iron on the 356 engines, having proven to themselves the right cast iron cylinder was as efficient as the biral.

I appreciate your observance of the on-going 94mm controversy, and reminded of how again we can be swayed by ad copy.

[Ol'fogasaurus]

FJ wrote: "... I had heard from reliable sources that there were poor castings and inferior metallurgy in some cylinder products compared to others. Certain iron alloys were too brittle, some too soft. …"

This is very true. (not pointing fingers) Some of the tools and materials out there will break if too much loading is put on them because of the porosity (https://en.wikipedia.org/wiki/Porosity) of some of the materials. The standards from area to area are not always the same. A long time problem.

Lee

[Bruce2]

I think the complaints went away from 94s because 94s make a lot of power, and most guys want power over longevity. Many guys reported 20-30k miles from a set before they needed a re-hone. And for a toy car, that's sometimes a decade worth of driving. A lot of guys will be tearing down their engine sooner than that anyway to make changes.
I'm going to perform your "tap a bare cylinder with a steel wrench" test to see what happens. I've got a couple of NOS Cima cylinders. I'm not holding my breath though. I don't think anything made from cast iron would ever ring.
I think it's the iron of the cylinders that is critical to long life. Brazilian Cimas have proven themselves. I can't say the same for anything China.

[Ol'fogasaurus]

If that is what you are referring to as the "OK brazilian case", I would double-check those crank and rod bearing journals and flush out all the oil passages really well. Also, it appears there's a crack in the top of the case near the 2nd case stud.

Good eyes Mike!