96 mm cylinder question, Difference between 1.7- 2.0? Options

[Jgilliam914]

I was digging through a storage tote and found a set of NPR 96mm pistons and cylinders.
Is there a difference between one that fits a 1.7 vs a 2.0?

[brant]

Yes.
Wrist pin height as you have to use the rods for 2.0/1.7

[ClayPerrine]

Yes.
Wrist pin height as you have to use the rods for 2.0/1.7

Brant...


Why do you say that? I ran a 1.8 crank and rods with 2.0 pistons and cylinders for years. Is there something I don't know and got seriously lucky?

[bdstone914]

Yes.
Wrist pin height as you have to use the rods for 2.0/1.7

@Brant

Why do you say that? I ran a 1.8 crank and rods with 2.0 pistons and cylinders for years. Is there something I don't know and got seriously lucky?

interesting. the 2.0 crank was made by offsetting the rod journal. I believe the wrist pin height is different between the 1.8 and 2.0 pistons. Could it be that the 2.0 pistons on 2.8 rods positioned the piston correctly?
Clay, Do you remember if you shimmed the barrels and what deck height you ran? (IMG:style_emoticons/default/popcorn[1].gif)

[ClayPerrine]

Yes.
Wrist pin height as you have to use the rods for 2.0/1.7

@Brant

Why do you say that? I ran a 1.8 crank and rods with 2.0 pistons and cylinders for years. Is there something I don't know and got seriously lucky?

interesting. the 2.0 crank was made by offsetting the rod journal. I believe the wrist pin height is different between the 1.8 and 2.0 pistons. Could it be that the 2.0 pistons on 2.8 rods positioned the piston correctly?
Clay, Do you remember if you shimmed the barrels and what deck height you ran? (IMG:style_emoticons/default/popcorn[1].gif)

I did not have to shim the cylinders. It has been a long time since I built it, so I don't remember the deck height measurement. But I never had a problem with any interference between the pistons and the head.

[brant]

well now I'm confused too....

the stroke on a 2.0 is 70.4
and on the 1.7 and 1.8 cranks it is 66mm

I haven't built a 1.7 or 1.9, but always understood the rods had to match the crankshaft.

and they make pistons with different wrist pin heights to match the rods/total length of each set up.

brant

[Artfrombama]

Are the rods between 1.7, 1.8, 2.0 different lengths?

[brant]

Are the rods between 1.7, 1.8, 2.0 different lengths?

That’s my understanding
1.7/1.8 are the same

2.0 rods are different

[Montreal914]

2.0 rod has a smaller crank end diameter due to 2.0 crank being a 66mm crank with reduced journal to create the extra offset (stroke). Not sure I properly explained this… (IMG:style_emoticons/default/rolleyes.gif)

Edit: said differently… the 66mm crank has 55mm journal whereas the 71mm crank (2.0) has 50mm journal. The 5mm is machined offset on the 66mm crank to create the 71mm stroke. Therefore rods are different between 66 and 71, as mentioned in previous posts.

[ClayPerrine]

2.0 rod has a smaller crank end diameter due to 2.0 crank being a 66mm crank with reduced journal to create the extra offset (stroke). Not sure I properly explained this… (IMG:style_emoticons/default/rolleyes.gif)

Edit: said differently… the 66mm crank has 55mm journal whereas the 71mm crank (2.0) has 50mm journal. The 5mm is machined offset on the 66mm crank to create the 71mm stroke. Therefore rods are different between 66 and 71, as mentioned in previous posts.

Yes, but at Top Dead Center is the distance from the crank centerline to the piston top the same on a 1.7/1/8 and a 2.0? I would suspect it is, as they didn't change the case sides to account for the longer stroke. The smaller journal on the 2.0 would account for the difference in rod length at TDC. All the additional displacement comes from the additional distance at BDC.

A 2.0 smaller offset rod journal may not necessarily have the same distance from the case side to the highest point on the rod journal. The differences in the rods would account for that.

Do I make sense??

[davep]

Said differently, the rods differ due to the size of the big end, predominantly. As to the length of the rods, and thus the positioning of the piston face at top dead center that I do not know. But if Clay can successfully run a 1.8 crank and rods with 2.0 pistons and cylinders then it appears all is well.
AFAIK, the cylinders are the same height, and the pushrods are the same so the overall width of the engines do not change. Therefore the only possible difference in the 96mm set could be the position of the wrist pin.

[914sgofast2]

The 1.7 liter and 1.8 liter rods are the same length. The 2.0 liter engine's rods are a different length because the 2.0 engines have a different crankshaft stroke.

The two types of 96 mm diameter pistons available for these engines are also different. The pistons used in the 2.0 engine and the 96mm pistons used with the 1.7 liter and 1.8 liter rods have different piston pin heights within the pistons.

When aftermarket 96mm "special big bore" pistons are used with the 1.7 or 1.8 engine's rods and crankshafts (along with 96mm cylinder barrels), it will only yield a 1912cc displacement, not a true 2 liter displacement.

If you want to turn your 1.7 or 1.8 engine into a true 2 liter engine, your need to use a 2.0 liter crank and 2.0 liter rods. These are "bolt in" updates to the engine case without modifying the case.
Cylinder heads are a slightly different matter. The 1.7 heads will need to be fly-cut to accommodate the larger outer diameter of the 96mm cylinder barrels. The 1.8 heads do not need to be fly-cut, and have a head/combustion chamber diameter which will handle the larger diameter 96mm cylinder barrels.

[Front yard mechanic]

Nice can you build one for me

[Dave_Darling]

If you measure the rods end to end, they are the same length or pretty close to the same length. If you measure from the center of the journal to the center of the wrist-pin hole, the 2.0 rods are 2.5mm longer. The 2.0 rod journals are smaller diameter, but with the center of the journal moved outward by the same amount as was cut off.

The 2.0 pistons have a different wrist pin height, AFAIK, to compensate for this.

Note that the 96mm barrels that fit into 1.7 heads are thinner than those that fit in 1.8 or 2.0 heads. The registers where the cylinders fit in a 1.7 are 100mm, leaving only 2mm thickness for the barrel at the top. The registers for 1.8 and 2.0 heads are 105mm, leaving 4.5mm thickness for the barrel. Generally the thicker one is better.

--DD

[zig-n-zag]

I measured the wrist pin to the piston top for a 90mm piston and it’s 42mm. The 94mm bus piston is at 35.6mm. I assume the 93mm piston would also be 42mm. Interestingly, a Cima/Mahle forged type 1 94mm stroker piston has a pin height of 35.3mm.

The rod length center to center for the 1.7 and 1.8 is 127mm and the 2.0 rod length is 131mm.

[914werke]

I measured the wrist pin to the piston top for a 90mm (1.7L) piston and it’s 42mm.
I assume the 93mm (1.8L) piston would also be 42mm.
The 94mm (2.0L) piston is at 35.6mm.

The rod length center to center for the 1.7 and 1.8L is 127mm
The rod length center to center for the 2.0L is 131mm.

So the 96mm (2.1L) piston for the 2.0L rod/crank would also be at 35.6mm
& to clarify that would be from wrist pin center-line to Piston top (IMG:style_emoticons/default/sunglasses.gif)

[914werke]

Note:
the 96mm barrels (P&C kits?) that will fit into 1.7L heads (w/o machining) are thinner than those that fit in 1.8 or 2.0 heads.
The registers where the cylinders fit in a 1.7L are 100mm, leaving only 2mm thickness for the (cylinder) barrel at the top (where if fits into the head).
The registers for 1.8 and 2.0 heads are 105mm, leaving 4.5mm thickness for the (cylinder) barrel. Generally the thicker one is better.
--DD

Dave I keep hearing this same info regurgitated on the interwebs but Ive never encountered such a set of 96mm cylinders & Im not aware of anyone that actually sells them ?

[cgnj]

NPR slipper pistons were a thing in 80's and 90's. They were made to drop in a 1.7 with 1.7 heads. Since the 1.7head register is smaller, the difference was made by reducing the cylinder thickness. The was no internet in those days, so how reliable that was is a question that I wouldn't be the one to experiment to find the answer.

[Dave_Darling]

There were kits sold for 1.7s that did not require machining. I remember seeing the ads for them, and corresponding with people who had used them. Most were happy with them, some had run into sealing issues.

--DD