Project X

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teazer
Posts: 900
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Project X

Post by teazer »

I think you hit the nail on the head with O rings being too close to the bore, and therefore getting too hot.

I suspect that the issue is the inability of a stock stud spacing to provide adequate and consistent pressure. Studs are al over the place and it is probable that it allows the head inserts to flex enough to allow combustion gas to reach the rings. Possible alternate fixes are to move the O rings out further away from the bore and/or to bolt the inserts to the block the way that Brett deStoop did on his super high HP motors. He had a relatively thick dome (insert) retained by a ring of evenly spaced small bolts to apply even pressure.

One company here in the US that offers inserts has made them with a wall around them to add stiffness. I feel that that's a poor design from a heat transfer perspective but it adds stiffness. They still blow head gaskets from time to time, but it's easy to understand why they make them that way. So that might be another avenue to explore.

I seem to recall that people used Wills rings in Hillman Imps to help them seal and they had aluminum blocks and heads, so a similar problem they were trying to solve. And let's not forget that you will make more HP than any Imp and the other thing to remember that peak cylinder pressure is approaching 100 bar just after TDC. That's a lot of pressure to try to contain. Stiffness helps there as does secondary sealing with things like Wills rings. Another way is to use a head gasket with the correct bore and solid wire ring that bites into the gasket fire ring. And add a secondary wire ring at a larger diameter in the head to create a second pressure dam, so to speak.
burgs
Posts: 66
Joined: Mon Feb 06, 2012 9:07 pm
Location: Hunter Valley NSW Australia

Re: Project X

Post by burgs »

Hi
Teaser I raced speedway (cars) and in my wisdom I decide to race a Subaru, I fitted a 1600cc engine bored out to 1700cc and turbo charged it big time, short of it is the head gasket would not hold, so I O,ringed the head and was told to use piano wire as the o ring, never had any more issues with the standard head gaskets but had heaps of other issues mainly fuel/forged pistons with holes burnt :shock: couldn't afford dyno time :oops: .
Burgs
madforitkev
Posts: 242
Joined: Tue Dec 13, 2016 7:21 pm
Location: Poole

Re: Project X

Post by madforitkev »

So made some progress. MK2 of the Wills rings all done.

My first ones were a bit small on diameter and not sealing against the outer face.

New ones below with the compression holes cut in.
rings3.jpg
rings4.jpg
Problem I have now is a tolerance stack. As my original design was O rings which while having a similar compression groove diameter to the wills rings, do give a bit more and spread over the squish head outer band nicely.
The copper rings, now at the right outer diameter are sealing right on the edge of the squish outer diameter and somewhere near the middle of the ring (hard to explain, even harder to photograph). Bottom line is I need more sealing face in touch with the ring especially as there is a couple of mm in the tolerance of the head bolt positions and the head has horizontal movement as a result!

As my water jacket to liner dimension is so tight, the only way round it is to do squish MK2 with a wider diameter.

So I have decided to save that to the final build and for now have the wills rings installed with a normal head gasket as well. I loose about 20 psi in static compression (now at 125psi) but at this stage of the dyno runs it is more about getting the exhaust to work properly. So I have started to put it all back together again. :D

One other improvement this time round (along with the slide in stinger sizes) is the front (hidden) mini radiator just to drop the temp a bit more.
rad2.jpg
Its actually a scooter oil cooler with a surprisingly big bore so it should be OK.
Honest baby....this is probably the cheapest bike I have ever bought!!
teazer
Posts: 900
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Project X

Post by teazer »

125psi is a little lower than we want and 105 will lose a bit of HP. Mine used to run 165psi cold and now is down to 155 after the last round of porting changes raised the exhaust port.

When using a stock type head gasket, be sure that the bore diameter is small enough.. Gaskets are typically 75 -77mm bore and that allows them to blow. The only gaskets I use are Cometic which they make to order and I usually go 0.5mm over the nominal bore size to allow for slight misplacement.
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Alan H
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Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: Project X

Post by Alan H »

After the rebuild on my +1mm L barrelled Hippo which took a couple of head gaskets out ( viewtopic.php?f=13&t=9121&hilit=Hippo&start=150 ) we found out the barrels had been decked - 1mm off the bottoms - which gave 150psi cold. Vibrated like a barsteward at 6k rpm and didn't like to rev much over 5k really. Ended up with A barrels (still +1mm over and comp was 120psi.)
Runs ok over the last four years, but it is a road bike.....
Proof that four strokes are over complicated
teazer
Posts: 900
Joined: Mon Mar 07, 2011 8:10 pm
Location: Chicago

Re: Project X

Post by teazer »

That's interesting. Mine runs 12 second quarter miles and revs nice and clean all the way to about 8,000. But it's a different beast all together. Bob Prior uns 10s and maybe less in a stock heavy chassis.

With higher compression, it's usually necessary to take out some ignition lead. Mine ran best at 19 degrees BTDC IIRC. Stock timing and high compression are great at low revs but become problematic as revs rise because peak pressure would have occurred too early and would cause excess cylinder pressure rise before TDC. A decent exhaust system exacerbates timing problems.
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Alan H
Posts: 11457
Joined: Fri Aug 05, 2011 6:38 am
Location: Wombwell, Republic of South Yorkshire

Re: Project X

Post by Alan H »

It was (and is) standard timing on points and your observation makes sense. The crank was balanced apparently, but I was told after that it doesn't make any difference - except to the price of the rebuild! I was told it has had Allspeeds (Short Gibson style) on since 1979 and it does go well with them on. Not to your standard of course!!
New colours.jpg
Proof that four strokes are over complicated
madforitkev
Posts: 242
Joined: Tue Dec 13, 2016 7:21 pm
Location: Poole

Re: Project X

Post by madforitkev »

I will get there with the had now I can see the issue.

For now I need to take a break from heads and work on something else.

Once its running again I need to get the cooling running better and fit the new front engine mounts. The old design restricted head replacement too much and only relied on one bolt per side where the new version in effect uses all the barrel bolts for support as the support boss is welded to each side of the barrel. It looks tidier as well.

Once I'm happy the pipes are close I will switch to the fuel injectors and see how close I can get them to run.

Later......
Honest baby....this is probably the cheapest bike I have ever bought!!
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