Problems installing Andrews x3 camshafts

v.f. wrote:

Of course I did the math; I use a proven calculator to calculate compression ratio. And with my data, I need to reduce the combustion chamber by about 3.5 cm³.The original combustion chamber on the J engine is 40 cm³. After installing larger valves and adjusting their sag to accommodate the 3X camshaft, my chamber increased to 46.5 cm³.Removing 1 mm from the head is about 3.5 cm³.If I'm wrong, please correct me.

 

Your original question was how much to remove for a "2cc" reduction which was approx 0.53mm so if you are now looking for a 3.5cc reduction then approx 1mm would be correct. The calculator looks great but unfortunately I can't read Russian   On the face of it though with a huge overbore and those high domed pistons I am surprised you need to skim the head (even taking into account the increase chamber volume from the head work) but sounds like you are all over the math. Should be a beast

The only place I could have gotten it wrong was the piston displacement. I'll try re-priming the piston this evening and recalculate. These are old MTC pistons that I bought about 15 years ago along with the block. Unfortunately, the specifications are gone. But I remember the piston-to-cylinder clearance is about 0.001 inches. And I think they're about 13-1. But I'm not sure.)))
Yes, the question was about removing the pistons to get -2 cm³, which is probably 0.7-0.8 mm. I was hoping someone had some verified information.The calculator shows a decrease in compression ratio when installing a non-standard camshaft. On the 3X, the intake valve closes at 65 degrees after TDC, which results in a decrease in compression ratio.Perhaps the translator didn't convey the idea quite accurately.

v.f. wrote:

Removing 1 mm from the head is about 3.5 cm³.If I'm wrong, please correct me.


 

That's about right.
I had to skim 1.3mm off my last J head to reduce it 4cc and achieve a 36cc chamber volume for use on an earlier 903/1015 Z motor.
Due to the curvature of the combustion chamber you may need to sneak up on it with a couple of passes after cc-ing in between if you need to hit your target chamber volume exactly..


 

I understand it's hard to get the right size the first time, so I'm gathering information from those who've done it before. I really don't want to have to take the cylinder head in for resurfacing multiple times.)))

zed1015 wrote:

v.f. wrote:

Removing 1 mm from the head is about 3.5 cm³.If I'm wrong, please correct me.


 

That's about right.
I had to skim 1.3mm off my last J head to reduce it 4cc and achieve a 36cc chamber volume.
Due to the curvature of the combustion chamber you may need to sneak up on it with a couple of passes after cc-ing in between if you need to hit your target chamber volume exactly..



 

Rob do think it would need that much with an 82mm bore and those high dome pistons ? (it is if I remember correctly, a "J" motor in a GPZ1100B series)

Wookie58 wrote:

Rob do think it would need that much with an 82mm bore and those high dome pistons ? (it is if I remember correctly, a "J" motor in a GPZ1100B series)

Most off the shelf piston kits regardless of overbore size and their advertised comp ratios are designed to work with the stock combustion chamber volume so if the volume has increased substantially due to pocketing the valves etc then the head will need skimming to get that volume back down to the stock figure or whatever is needed for the target comp ratio.
 

v.f. wrote:

I understand it's hard to get the right size the first time, so I'm gathering information from those who've done it before. I really don't want to have to take the cylinder head in for resurfacing multiple times.)))

It's tricky getting the volume correct first time and unlikely if you need to be particularly exact especially if just taking the head to a machine shop and telling them to remove a set amount.
You need to have the head perfectly level, fill the chamber with the right amount of fluid and measure down to the surface but accounting for the meniscus is hit and miss.
A proper engine shop will cc and skim then cc again etc until the desired volume is achieved which may take several passes but that is what you pay for.
Luckily i have my own mill so can ruin heads at my own leisure for no extra cost 

 

Looking at your calculator is your piston dome volume -14.2? (should be the only negative number)

That seems too low because on my 80mm pistons it was about 19cc (picture shown) and that piston has been milled down, so I would expect yours to be more. The picture below is how I roughly calculated my volume on that old MTC piston.

 

 

 

Yes, everything is correct, the engine is precisely gpz1100b2.

In our "great and powerful" country, there's a major problem with machining. Many don't want to take on such work; it's easier for them to bore car cylinder blocks and generally focus solely on cars. And some want to do this work for big money, but they don't have the skills or understanding of what needs to be done.We have a problem with motorcycle culture in general, and vintage motorcycles are a real disaster. So, to be on the safe side, I'd rather reduce the cost, take measurements myself, and adjust if necessary... That's our reality.

I took new measurements... and found that I lost 2 cm³ somewhere. Overall, I now measure 16.4 cm³.Which isn't so bad. With the current values, the geometric compression ratio will be ~10.3. So, as a preliminary, I can remove 0.2 - 0.3 mm from the cylinder head.I measure the piston displacer differently. I have old 82 mm sleeves. I lower the piston into the sleeve by 15 mm - so that the displacer is flush with the edge of the sleeve - and flush it. Then I calculate the volume of the sleeve, which is 82 mm in diameter and 15 mm deep. After that, I subtract this from the sleeve volume - the result of the flush. This works on cars. I think it works here too.)))

The displacer on the 80mm piston is visually larger because the piston diameter itself is smaller. It seems to me...)))By the way, regarding piston rings, if you're interested. The Honda B18B engine with a cast-iron block has a piston diameter of 81mm, but there's an oversize of 82mm, and the ring thickness is the same as MTC 1-1.2-2.8 rings. However, MTC rings cost $160, while Honda rings are slightly cheaper.)))