Kent cam regrinds GK73a

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moforockband
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Kent cam regrinds GK73a

Post by moforockband » Thu Jul 27, 2017 9:22 pm

I'm a bit fed up of getting left for dust to zxr400's and the like, and wanting to get a more revvy nature to the 73a motor, hopefully improving on the linear 59hp it was designed for.

Kent offer 2 grind options for the 73a at a reasonable £158 +vat.
They offer a mild street grind, to a juicy 1mm overgrind to the stock cams. Kent add a certain treatment to the cams after the grind.
I'm going for the race option, so will post the results. I will solder check the clearances between valve and piston before and after assembly.
If anyone can advise a safe clearance for these old engines, I would appreciate it.

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Re: Kent cam regrinds GK73a

Post by Variablevalves suck » Fri Jul 28, 2017 9:07 pm

Think we will always play second fiddle to the zxr's the downdraft nature of the zxr gives good power with little work, those tuned bikes are pushing upper 60 HP, I sold Mike at BMC a to beet pipe for his zxr and it was over 70 on the dyno.

I've thought about a regrind but the stock cams are fairly fruity if I remember but run odd timings compared to other bikes, some careful dialling might work well.

Its that long since I measured the internals but remember most of the kit timings for zxr, fzr etc were very similar but well away from the 73a.

The kit book for zxr and nc were on this site so Worth find them out and doing a compare.

moforockband
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Re: Kent cam regrinds GK73a

Post by moforockband » Tue Nov 20, 2018 10:09 pm

Have some info on the cam mod.
I went for F351 and F1004 kent re-grinds which all in all end up around 0.9mm more valve lift. I will run these on stock valve gear and see how we go. These are race cams, and kent does offer a milder street option, and an even madder race grind. You have to be careful with the gsxr400 engine as the tolerances are really tight. I measured 1.30mm piston to valve clearance on the inlet, but couldn't get a definitive answer on the exhaust as I left too much carbon on the valve. Minimum clearances are 1.27mm inlet and 1.6mm exhaust.

std suzuki gk73a cam data:
5.23mm cam lift with 7.6 valve lift (inlet)
4.9mm cam lift with 7.0mm valve lift (exhaust)
Rocker ratio approx 1.43

Kent cams data:
5.87mm cam lift with approx 8.5mm valve lift (inlet)
5.55mm cam lift with approx 7.9mm valve lift (ex)

I think the kent option is safer than the megacycle option, as the exhaust cam is a little milder (and the exhaust valves run tight on this motor). You have to wind the tappets right in using the Kent cams, which is a downside.

moforockband
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Re: Kent cam regrinds GK73a

Post by moforockband » Sat Aug 10, 2019 12:24 am

Took me 2 years to build the motor. I've put 400 miles on it, and she's going OK. A little more valve noise than normal, but it's stayed together and I have took it all the way to 15000rpm. It's a non sp 73 engine.
It has the midrange of an old 600 now, but is lacking the top end zip I was after. I skimmed 0.06mm off the barrel also.
Had to jet it right up to 150 ish on the mains, but I think something in the motor is holding it back at the top end. Maybe the ports.
But it is faster than what it was, so there is some bonus.

moforockband
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Re: Kent cam regrinds GK73a

Post by moforockband » Wed Aug 14, 2019 9:09 pm

Sorted it, put some even higher flow air filters and 136 jets. She flys now. Nearly too fast for the chassis :)

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Re: Kent cam regrinds GK73a

Post by Hubbskiboy » Mon Sep 02, 2019 5:46 pm

Bung some videos on YouTube when you get a chance.
I want to see how well that thing goes round a track or even a nice quiet road.

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Re: Kent cam regrinds GK73a

Post by Tom123 » Wed Sep 04, 2019 11:15 am

Do you have any contact details for Kent cams? I’m in the process of rebuilding a gk73a sp engine and the cams have pitting on them was hoping I could get the reground

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Re: Kent cam regrinds GK73a

Post by moforockband » Wed Sep 04, 2019 4:47 pm

01303 248666. Make sure the pitting is not too severe and not on the journals. The inlet cam you have is quite rare ( a j model one iirc from the sp).


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