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Hey guys, just rebuilt this motor with Wesico 11.5:1 pistons, started up and it is knocking pretty bad. It had a re ground crank with oversized bearings so that is not the issue... checked valves a couple times, not that.
 

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Timing was set right during assembly and rotated the assembly by hand to check clearance before putting into the bike. kind of thinking maybe there is a loose chain, but I don't have any experience with anything other than stock pistons. Is there a common problem with the higher compression pistons not having enough clearance?
 

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I researched a little.... Looks like I may have aftermarket cams, and they do not have enough clearance to run properly with these Wiseco pistons. Got another 750 apart that I can swap the cams out and see if this is the case. thanks for the lead Nmkawierider.
 

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Timing was set right during assembly and rotated the assembly by hand to check clearance before putting into the bike. kind of thinking maybe there is a loose chain, but I don't have any experience with anything other than stock pistons. Is there a common problem with the higher compression pistons not having enough clearance?
I have high comp wiseco pistons in mine with newer Brute cams. I did the modeling clay check for clearance and there was oodles of room.
Those aftermarket cams would have to be pretty extreme to hit. The 2015 BF750 aren't crazy, but they're more than stock.
 

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I would be very surprised to see the valves hit the Wiseco pistons.
 

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Any aftermarket cam that is a little beyond mild lift and duration over stock cams will smack a Wiseco off-the-shelf piston. They have very little relief cut in for valve clearance. Pretty much any builder’s cam or anything over the mild grind from Web Cam is a no-go.
 

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They have very little relief cut in for valve clearance.
Actually, that's not true. Look at the above photo. Wiseco have a pretty big valve relief cut in. Way bigger than stock.
 

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Actually, that's not true. Look at the above photo. Wiseco have a pretty big valve relief cut in. Way bigger than stock.
I just had my engine rebuilt with Wiseco pistons and could only use the mildest Web or 2015 BF cams bc there wasn’t enough clearance for anything more aggressive. That is straight from Brad at BKP. They didn’t have their 730 kit in stock and couldn’t get the pistons for another month, so I opted to do the build with Wiseco pistons I already had and use 15 BF cams. If I could, I would done the 389 Web trail cams (I think that was the number).
 

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I just had my engine rebuilt with Wiseco pistons and could only use the mildest Web or 2015 BF cams bc there wasn’t enough clearance for anything more aggressive. That is straight from Brad at BKP. They didn’t have their 730 kit in stock and couldn’t get the pistons for another month, so I opted to do the build with Wiseco pistons I already had and use 15 BF cams. If I could, I would done the 389 Web trail cams (I think that was the number).
Those cams must be huge because the photo I took above is with 2015 BF750 cams and the wiseco 11:5:1 pistons. There's more than a quarter inch of clearance. You could adjust the valves on the wrong stroke and still never come close to hitting.
 

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Those cams must be huge because the photo I took above is with 2015 BF750 cams and the wiseco 11:5:1 pistons. There's more than a quarter inch of clearance. You could adjust the valves on the wrong stroke and still never come close to hitting.
Yes they have a nice valve relief but not enough for stage 2 or 3 cams that most builders like BKP or even Web’s more aggressive cams. Not saying it’s the case every single time with every single cam out there, but getting a builder’s cam to work a Wiseco pistons is the exception, not the rule. If OP’s bike had a bbk from a reputable builder and not some eBay special that’s a hodgepodge of off the shelf components sold as a bbk, it’s very possible his valves are contacting the piston.

Here’s the BKP stock bore high compression kit. The reliefs are cut way deeper than the Wiseco pistons I had installed. Believe me, I was ready to have them build this engine with their stage 2 cams and he said no way it would work with the Wiseco pistons. I really like the way it turned out the 15 BF cams though.

75390
 

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We know the 2015 bf750 cams have valve clearance with Wiseco's about the width of the clay in my pic, right?So, if Big Kev is saying his cams will not work with Wiseco's pistons, then the difference in his lobes vs the '15 BF750 lobes is greater than the width of that clay. That's a pretty damn big cam.

As for his pistons, it's hard to say what the real valve relief is going to be just by looking at the depth of the valve relief pocket. That's only the difference from the face to the bottom of the pocket. A taller piston will usually have a deeper looking pocket, and a higher compression. But what I'd really like to know is the measurement difference between the two pistons of the centerline of the wristpin to the bottom of the pocket.
 

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Also, quick question Kickstart. Where did you buy your Wiseco pistons?
First ones came from RMATV. Second one came from Ebay because RMATV quit selling them.
 

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We know the 2015 bf750 cams have valve clearance with Wiseco's about the width of the clay in my pic, right?So, if Big Kev is saying his cams will not work with Wiseco's pistons, then the difference in his lobes vs the '15 BF750 lobes is greater than the width of that clay. That's a pretty damn big cam.

As for his pistons, it's hard to say what the real valve relief is going to be just by looking at the depth of the valve relief pocket. That's only the difference from the face to the bottom of the pocket. A taller piston will usually have a deeper looking pocket, and a higher compression. But what I'd really like to know is the measurement difference between the two pistons of the centerline of the wristpin to the bottom of the pocket.
That’s a fair assessment and only going by what I was told.

I asked the question about where you bought your pistons bc I’m curious if you got them as they are sold off the shelf or if they were a modified piston made for big cams. There are a few builders that cut Wiseco pistons for their cams. It’s difficult to tell from your pics how deep the relief is (at least looking on my phone). From a glance they do look deeper than the Wiseco that I used but can’t really tell. Maybe it’s the difference in the pistons made for the BF750 and SRA bikes...I dunno really.
 

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That’s a fair assessment and only going by what I was told.

I asked the question about where you bought your pistons bc I’m curious if you got them as they are sold off the shelf or if they were a modified piston made for big cams. There are a few builders that cut Wiseco pistons for their cams. It’s difficult to tell from your pics how deep the relief is (at least looking on my phone). From a glance they do look deeper than the Wiseco that I used but can’t really tell. Maybe it’s the difference in the pistons made for the BF750 and SRA bikes...I dunno really.
All of my Wiseco pistons have been their off the shelf, +2mm, 11.5:1 pistons. That's 84mm. The Brute 750 standard bore pistons from Wiseco are 85mm and also 11.5:1. They should have the same profiles.
Which ones did you buy?
 

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All of my Wiseco pistons have been their off the shelf, +2mm, 11.5:1 pistons. That's 84mm. The Brute 750 standard bore pistons from Wiseco are 85mm and also 11.5:1. They should have the same profiles.
Which ones did you buy?
Off the shelf 82mm for P/BF650 (I have an 08 BF650 SRA)
 
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