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Author Topic: AA pistons with different hight solutions  (Read 795 times)
Tom58
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Posts: 10


« on: January 20, 2018, 16:42:43 PM »

Guys,

Need some advice to set up the right deck hight. When pre assambling the engine we messured at one cilinder quote a difference.

I'm building a new 2176cc typ 1 engine (78,4 x 94).
Using a set of AA 94mm 'b' piston and cilinder set.

Set up all the things an messured everything.
-case is cut out on same hight.
-cilinders are all 4 same hight, also when mounted on the case.
-all pistons are same weight.

Sadly one piston is about 0,15mm 'shorter' when messured from top pistonpen to top of cilinder.
In my opinion it is not an option to cut down this cilinder slidly more to came to the same deck hight, because in this case the cilinders are not equal on hight.

My first toughts are:
Shorten the other piston on the same 'engine side' to the same hight as the shorter piston. Cut those two cilinders down the same lenght to the right hight. All 4 cilinders came the same deck hight.. because there is cut off some material, machined all pistons to the same weight.

But maybe you guys have some advice or opinions?
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K-Roc
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Posts: 188


« Reply #1 on: January 20, 2018, 17:32:18 PM »

First try other pistons in that location.  your problem could be in the crank or the rod length as well. are the rods new or rebuilt? was the crank reground? ... if you confirm 1 piston is in fact .005" taller,  I would cut that piston down in the lathe then re balance all 4.  ( fix the part that is incorrect )

you might be able to just move the pistons and rods around  and get things closer.

you could also slide 2 pistons side by side on to 1 piston pin, and compare that the piston tops are even with each other.






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andy198712
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Posts: 925



« Reply #2 on: January 20, 2018, 23:54:45 PM »

yeah i think you want to switch rods and see if the issue moves with the rod?
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GARRICK.CLARK
Sr. Member
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Posts: 273


« Reply #3 on: January 21, 2018, 21:15:23 PM »

I had this with my AA Piston kit.
I made sure the cylinders were equal on each side, you bolt a pair of cylinders down, (no pistons fitted) put a straight edge ACROSS the cylinders and measured any gaps with a feeler gauge between the cylinders and the straight edge . trimmed down the long cylinder out of the pair, once these were equal.(took 2 or 3 goes to get right), then switched my attention to the pistons, fitted 3 and 4 piston ,measured those, trimmed the crown on the longer piston to match the shorter one on 3 and 4  ,did the same for 1 and 2, then had to measure the deck on all 4 pistons then cut equal amounts from the crowns of 3 pistons to equal the largest deck height out of the 4 pistons. Proper ball ache.
The cylinder heights is a big one, it has to be right or you'll leak compression.
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Tom58
Newbie
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Posts: 10


« Reply #4 on: January 23, 2018, 20:04:45 PM »

@K-Roc and Andy, thanks for your answer!
I have moved the piston with the same cilinder on other places and switch the piston also with other cilinders. But every time i got nearly the same 'difference' with this piston.
This would show that the rods (some new h-beam) are equal, but I wil messure the rods a second time to be sure Wink

@GARRICK.CLARK;
Thanks for the reply, straight answer! It's like I had in my mind to be the next step.

How did you trimmed your pistons? With an milling/lathe? (Sorry don't know if thats the right translation)

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Martin S.
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Posts: 715



« Reply #5 on: January 23, 2018, 20:24:49 PM »

It is a good idea to check your parts ASAP for measurements and send it back if it isn't right.
AA means DIY QC.  Wink
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Cal Look white 68 Bug with AJ Sims EFI Turbo 2332. 194hp 240tq @ 5500 rpm 3psi boost.
Tom58
Newbie
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Posts: 10


« Reply #6 on: May 03, 2018, 18:18:33 PM »

The 'problem' is solved now:).

Had contact AA about this, but they say its within the specs,
So I've made some ours in the garage and took it the way Garrick.clark sad.
First made the cilinders, then the pistons machined to the one with largest deckhight.

Thanks for the answers and advice!

This one can get closed;)
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GARRICK.CLARK
Sr. Member
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Posts: 273


« Reply #7 on: May 03, 2018, 19:02:09 PM »

Good news Tom on getting the cylinders equal in length and the deck heights correct.
Makes for a better engine. Cylinder head chamber and port volumes is another time consuming job, also getting the chamber SHAPE equal on all 4 chambers.  
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dragvw2180
Sr. Member
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Posts: 279



« Reply #8 on: May 14, 2018, 19:33:52 PM »

For future use , the quick way to check your pistons is to install a wrist pin half way into one piston and then slide another one onto the other half of the wrist pin. The height should be exactly the same . Slide one off the wrist pin and check the rest of them the same way . If all measure the same you have eliminated the pistons as the cause of the difference in height . Mike McCarthy
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181
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Posts: 622


« Reply #9 on: May 16, 2018, 16:08:48 PM »

excellent piece of advice!
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