Cutting valve reliefs

[ppyvabw]

I know there's been some posts about this before but I have some specific questions.

Is it ok to cut valve reliefs in OEM cast pistons or is this definately a no no? DJE has some pistons with cut outs in them already on ebay, but they are standard bore, and I dont want to change the liners.

I have read that people made cutters out of old valves? How does one make the cutter?

[Coops]

I cut the reliefs in a set of cast stock pistons last year, and im running 100 shot of nitrous, i have had no probs yet.

you need to put a cutting edge on the valve face etc,
this is the one we made for doing my pistons,





and what it looks like after using the cutter,

[ppyvabw]

Yeah i saw your post.

How did you make the cutter? A small grinder and some needle files?

[Coops]

just a grinder and time

[sidecar]

A company called Power Train Products supplied short engines for some time after Rover stopped casting blocks themselves.

The PTP blocks went into morgans and possibly TVR's

PTP fly-cut the standard pistons on all their short engines.

HTH,

Pete

[kiwicar]

So PPYVABW
You'll be wanting a 1.76 chevy inlet valve like Tony then?
Pm me your address and I'll get one in the post to you.
Mike

[CastleMGBV8]

I shall be getting my new 4.35 engine test built next week so that we can measure everything so that we will know what additional machining to the heads and possibly the decks will be required to achieve the desired compression ratio

Just curious as to at what lift on a normal Rover engines valve cut outs become necessary.

The Crower 50232 has lift of .488 and advertised duration of 281 In. 285 Ex.

Also whats the normal piston to deck height clearance on a 3.9 engine?

Kevin.

[kiwicar]

Absolute lift is not really a guide it is the lift when the piston is at or close to TDC that counts, this is effected by LSA (overlap), cam ramp acam advance/retard the simplest thing to do is to mock assemble with a set of checker springs in the heads and plot piston to valve clearance for about 20 deg either side of TDC for inlet and exhaust valve with a dial gauge(use only 1 push rod so as not to have any accidents)
There is an article on Isky cams website on how to do it.
Mike

[sidecar]

Absolute lift is not really a guide it is the lift when the piston is at or close to TDC that counts, this is effected by LSA (overlap), cam ramp acam advance/retard the simplest thing to do is to mock assemble with a set of checker springs in the heads and plot piston to valve clearance for about 20 deg either side of TDC for inlet and exhaust valve with a dial gauge(use only 1 push rod so as not to have any accidents)
There is an article on Isky cams website on how to do it.
Mike

I did something like this with the engine that I'm building at the moment.

I used the spacer springs from an old rockershaft as the weak checker springs, cut them in half first and flatterned off the ends otherwise they are a bit too strong and will send the valve collets right across your garage when you remove the split keepers!

I also cleaned out a couple of old lifters and filled them with wax so that the small spring in the lifter could not be compressed as this will mess up your measurements.

I just set my piston at TDC when the valves were on "the rock" then pushed each valve down by hand until it hit the piston. To be honest I did not do a very scientific test either side of TDC because when I pushed the valves down they moved another 4mm before hitting anything! (My pistons have been fly-cut).

HTH,

Pete

[ppyvabw]

So PPYVABW
You'll be wanting a 1.76 chevy inlet valve like Tony then?
Pm me your address and I'll get one in the post to you.
Mike

Thanks, I'll let you know what I decide to do. DJE does +20 pistons with valve reliefs already in, but they are like 100 quid more than balanced pistons, and other than that, I think they might be exactly the same as stock pistons, but it saves me work, and potentially a cock up. Should decide in the next few days.