Forged M.A.P- Pistons

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Klaus Monning

Klaus Monning

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Hello,
I curently have casted M.A.P- pistons fitted. From the machining point of view they gave me a very, very, good impression. All the dimensions were equal between left an right side, and even the weight between them was equal to the last gram.
Now, after they were run in I gave the bike a really good run on the German Autobahn. I just wanted to try the top speed. I must add that I have a big- valve conversion (43/38mm), a compression ratio of 10,5:1 and an S 2 camshaft fitted. This means that I had to machine valve pockets into these pistons. After this top speed test I found that at a certain engine speed (between 3000 and 4500rpm) I have some kind of rattle in my engine. Allthough I'm not sure, I think it may be piston tilting. I also have to add that the piston to (cast- iron cylinder barrel)- clearance was something like 0,15mm which was a lot anyway.
Now the question: M.A.P offers forged pistons. Does somebody have any experience with those? Are they any good? I mean, if they are stiffer than the casted ones, they should be OK, shoudn't they? I must also add that I will definately not race the bike. But here and there it will get a real good thrash on the Autobahn. Certainly not over long distances but just for fun and for a few miles untill I close down the throttle, leaving the engine spin at 4500 to 5000rpm.
Once again the question: Has somebody experience with those forged pistons M.A.P offers for just 275 US$ or will I be the test animal?
 
Hallo, I had seen that fast Freddie had used them but in Triumph , and he seemed to be happy......may be more to come, and yes they are light , so it could be interesting as an alternative .....!
 
marinatlas said:
Hallo, I had seen that fast Freddie had used them but in Triumph , and he seemed to be happy......may be more to come, and yes they are light , so it could be interesting as an alternative .....!
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The ones I got for my Triumph are billet, not forged.
They do look very, very good. And even at 750, they are lighter than 650 pistons.
But I have not built the engine yet so have not tried them.
 
Moin Klaus,
I have a set of the Map Cycle 850 Billet Pistons and steel
rods but they are yet to be installed.
And yes they do seem to be very well made.
proof is in the pudding though.
hopefully in a couple of months.
 
What’s the oil pressure trend since rebuild? Any fluctuation?
 
A rattle that starts after a fast run doesn’t sound like a too-big piston skirt clearance problem. Can’t be certain though.

How’s the hot compression now?
 
Triton Thrasher said:
A rattle that starts after a fast run doesn’t sound like a too-big piston skirt clearance problem. Can’t be certain though.

How’s the hot compression now?
Click to expand...

Hello,
The oil pressure is ok. At 5 bars when cold and appr. 1.5bar when hot. It had always been like that.
I want to have a spare set: Cyl.- barrel with those pistons (I'm convinced enough for this test) and a spare cyl.- head with 41/35mm (Standard Yamaha XS 650) valves which I want to try.
Best Regards
Klaus
 
I meant compression in the combustion chamber, as measured with a compression tester. Sounds like you haven’t tested it, so I’m not being much help.

My point was supposed to be that if compression is lower on one or both cylinders now than it was before you went fast, then you have probably had a partial piston seizure or ring or small end damage from detonation.

You’ll know when you look.
 
I think some guys are like myself. I hate having to pull the engine apart. However, if you have got an old bike, you need a different mentality. If you've got a rattle, you have to find it before the big bang happens.
 
Klaus Monning said:
Hello,
I curently have casted M.A.P- pistons fitted. From the machining point of view they gave me a very, very, good impression. All the dimensions were equal between left an right side, and even the weight between them was equal to the last gram.
Now, after they were run in I gave the bike a really good run on the German Autobahn. I just wanted to try the top speed. I must add that I have a big- valve conversion (43/38mm), a compression ratio of 10,5:1 and an S 2 camshaft fitted. This means that I had to machine valve pockets into these pistons. After this top speed test I found that at a certain engine speed (between 3000 and 4500rpm) I have some kind of rattle in my engine. Allthough I'm not sure, I think it may be piston tilting. I also have to add that the piston to (cast- iron cylinder barrel)- clearance was something like 0,15mm which was a lot anyway.
Now the question: M.A.P offers forged pistons. Does somebody have any experience with those? Are they any good? I mean, if they are stiffer than the casted ones, they should be OK, shoudn't they? I must also add that I will definately not race the bike. But here and there it will get a real good thrash on the Autobahn. Certainly not over long distances but just for fun and for a few miles untill I close down the throttle, leaving the engine spin at 4500 to 5000rpm.
Once again the question: Has somebody experience with those forged pistons M.A.P offers for just 275 US$ or will I be the test animal?
Click to expand...

Hello,
I finally ordered these pistons, and imagine they arrived here in Germany (certainly from the US) within just 2 days. The shipper was FEDEX and M.A.P sent the pistons directly on Monday after I ordered them during the week- end (Sunday Morning). This deal was highly recommendable.
Just a word to the quality: Certainly they look absolutely beautiful and they seem to be very light. I give you further details as soon as I have meassured them.
Only the allready machined piston pockets have to be adjusted to my purpose. My valve sizes will be 42/36 (mm) in comparison to the standard 38/33 (mm). I will use (+1mm)- Kibblewhite Black Diamond Valves normally used for the YAMAHA XS 650. The additional machining job will be carried out by myself.
All the best Klaus
 
Fast Eddie said:
I don’t mind pulling an engine apart so long as I improve it.

I HATE putting it all back together the same. That just seems like I’ve missed an opportunity and wasted my time !
Click to expand...

I'm right in there now. I was almost hoping that something was wrong so I could rationalise some spending...sigh.
 
Hello
I have just meassured them. Here are the Results (they are absolutely equal)
Diameter at the lower part of the skirts are: 77,39mm. Diamter of tje pin-bore is: 17,47mm. The compression height is 37,93(5)mm. The pin- diameter is 17,45mm. The weight incl. Pin, rings and locating rings for the pin is between 320 and 321grams.
 
sorry Klaus, must have been typing at the same time.
Ick hab die pleuell und die kolben auch selbst gekauft .
 
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I suppose that you bought the long rods. I'm still using the short ones, well also M.A.P ones, but the aluminium version. Certainly if you use the short pistons (with the long rods) they are of course lighter. Anyway my pistons weigh 265 grams with rings locating rings but no pins. That must be the difference between the 2 stated weights.
 
No i also have the standard length rods,(steel) with the 77.5mm pistons.
just waiting to get my head and new cam back from the states and
bolt it all back together.
 
Hi, what clearance is advised by MAP for those pistons , even at 320 gr they are lighter than stock and nearly same weight than stock 750 ones .
 
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