Kent cam and piston clearance

[NicBowman]

Hi

Just dry assembled my Crossflow and checked piston clearances, using Kent 234 cam and Hepolite pistons. 90 thou overbore and full race head (huge valves).

I don’t see any clearance issue requiring mods? I was expecting to a need to machine the pistons?

Thoughts?

Thx


Nic

[xtruss]

Back in the day when i use to tinker with a kent engine - We had to have the valve pockets machined if fitting a kent 234.
Arrtical below taken from Burton power products.
The pistons are ideal for Kent engines running +0.090” pistons which are now in need of a rebore. In the past this would have meant going to expensive forged pistons (+.090” was the maximum size for a cast piston) or finding another engine block.

The pistons have 4mm deep valve pockets meaning they will fit most performance camshafts (including 234 and 244) without any further piston modifications.

[Astacus]

If you want to be sure, then get some plasticine and stick it to the top of the piston. Build the engine and turn it over by hand with no plugs, then take the top off again and examine the plasticine. If you cut it across the indentation you can easily see the level of clearance you have.

[VTC]

Do you still use the offset dowels ready for the timing or an adjustable gear these days?
the difference on mine was immense, the original engine builder had used a normal dowel on my piper 285/2 cam as i did not have an adjustable cam gear

[NicBowman]

Adjustable timing built into the duplex system. Need to set it up, but not tricky.

I have an endoscope so can look into the bore as it turns over (by hand). Works a treat, pretty cheap.

Nic

[timelord]

It depends on whether the block has been skimmed and on cam lift, with your 234 cam you should be ok its at high revs where things can touch, my Vixen was OK my my 1600M needed pockets cut in the pistons with the same cam as the block had been shaved to bring the compression back up after the +90 rebore

[NicBowman]

Hi Timelord

Thx. These pistons have 4mm deep pockets. The valves don’t appear to overlap even the piston top, I can see this very clearly with the endoscope. But, piston top gets close. Hence to me the pockets are all clearance. So I suspect it is good.

Best


Nic

[LLantrisant]

what pistons did you fit? the ones for a 1600 engine or the ones for the 1300 engines?

why i ask? usually you need to increae also the compression-ratio. just fitting a cam and an overbore will not bring the right horsepower, it may even get worse.

the easiest way increasing the comp-ratio is to fit 1300 pistons in the 1600 engine, but than you definately need to re-machine the valve-cutouts in the pistons.

[NicBowman]

Hi, I did know that, but will check the piston cutout volumes again.

Previous 'rebuild' had the old chambered heads plus chambered pistons and a non GT cam. So suspect it will be hard to produce less HP than that!

Thx


Nic

[NicBowman]

Yes, 1.3 pistons. Had me worried though, forced to go into the garage in my jimmies to check!

Nic