Short block long stroke engine

[2cams70]

None of the main suppliers were supplying correct plugs when I was looking 5 years ago. When I checked 5 years ago they were still a current part number from Ford. I was able to walk into a Ford dealer and order them. These fitted perfectly and were exactly the same as original in both length and thread specification. Ford part number is 87837ES2. Correct plug from Ford pictured

[Craven]

Re oil gallery plugs this has come up before, the reason they are so difficult to remove is it’s a NPTF thread. F part of code stands for FUEL this thread type is designed as a mismatch between the two parts locking together in a fuel tight manner, essentially distorting as its done up so really this is a use once fit after that the original thread form is lost so it’s not surprising replacement plugs don’t fit well.

[rgh0]

Re oil gallery plugs this has come up before, the reason they are so difficult to remove is it’s a NPTF thread. F part of code stands for FUEL this thread type is designed as a mismatch between the two parts locking together in a fuel tight manner, essentially distorting as its done up so really this is a use once fit after that the original thread form is lost so it’s not surprising replacement plugs don’t fit well.

In NPTF threaded holes and NPTF threaded plugs which was the original design for the block oil galleries the plus can seal without sealant as the thread roots and crest interfere to make a dry seal. Whether sealant was actually used or not on original assembly I dont know but i presume not given the design.

If you subsequently fit a hex socket NPT plug into the block it will screw in to around the same depth but require a sealant to seal the spiral passage at the crest of the threads as they will not interfere. However they should fit fine and not to far above the block front face surface. The general reason they stick to far above the block face is because its a BSP plug being used

cheers
Rohan

[ill_will]

The gallery plugs I have do indeed appear to be incorrect.

Reading up on it my understanding is 1/4" NPTF should be 60 deg flank angle and 18 TPI whereas the 1/4" BSP should be 55 deg flank angle and 19 TPI.

I measured 19 tpi using a set of Whitworth thread gauges (which have 55 deg flank angle) which were a snug fit.

Need to double check the threads in the block when I'm next there, but looks like this was the culprit as several of you pointed out -thanks!

[ill_will]

In response to some questions:

The pistons are from Dave Bean in the US, part number 560E0835. They are expensive, but very nice quality. The standard 125E rods have been crack tested and balanced and will have ARP bolts, so should be ok to 7500 rpm and even 8000 iirc. Crank is the steel Farnden EN19 unit from QED, I understand this is ok to 8000 rpm.

The plan is to aim for 10.5-11:1 CR. In the longer term I'm aiming to fuel inject it; certainly mapped electronic ignition. This will be for 97/98 RON (UK). I will be using some short duration high lift cams, approx 0.43" @ 285deg, DCOE40 size intakes, 1.6" and 1.375" valves.

I've been a bit distracted from the project recently due to rewiring another car, but will hopefully be back on it soon.

[ill_will]

Found some time to pick this up and made a series of unfortunate discoveries.

The first was after a trial assembly to check exactly where the piston crown sits relative to the deck. My understanding is ideally it would be bang on flush to give approx 0.040" squish, all from the head gasket thickness. From specs and measurements, expectation was the crown would be about 0.52 mm below the deck. This would then mean a set of 4.826" rods could be used to bring it approximately flush.

The crank is a 77.6mm stroke Farndon EN19 that I sourced from QED, and which they had shipped direct to Gosnays to balance as a whole assembly with the pulley, flywheel and clutch cover. After assembling cylinder 1 (no rings) I brought it up to TDC and the crown was about 2.8mm below the deck.

After some swearing, I rechecked the rod lengths (125E, ~4.8"), piston compression height (1.46") and, whilst I don't have big enough vernier I confirmed the crank CL to deck height with a tape measure to be approximately 198mm, which agreed with the 7.809" that Gosnays had measured for me prior to ordering everything. (Aside: the Dave Bean catalogue says 7.7" which had me confused?)

This left the crank, which unfortunately appears to be a short stroke not the long stroke ordered. To be fair, I should have asked Gosnays to check it at the time, but this is an annoying mistake. I spoke to QED today, and hopefully we can sort something out. Unfortunately the whole assembly has already been balanced though.

[snowyelan]

Could you check the piston stroke to verify its the crank?

[ill_will]

Yeah, should have said: doing this confirmed it was indeed a short stroke crank.

QED have been very reasonable and have offered to exchange it and pay for the balancing. Credit to them, they have been helpful any time there has been an issue.

[ill_will]

Some more slow progress on this.

I did some measurements and a test fit of the replacement crank (correct stroke now.) Bearing clearances all good, spins freely.

The piston squish 'flat' ring is approx 0.011 to 0.019" below the deck. With a gasket thickness compressed of say 0.043" (85mm Cometic CFM, for example) that would put the squish distance to the head at 0.054-0.062". I'm concerned that is a bit too much, and so I maybe need to fork out for some 4.826" rods (to give 28-36 thou)?

The other exciting bit of news is the head is ready, SAS full race spec but with slightly smaller inlet ports to suit DCOE40s, and hopefully keep gas velocity up at lower rpm for low down torque.

[rgh0]

I would be happy with the piston location as it is. The piston /rod assembly stretches as the piston moves over TDC and bearing clearances close up and the rod stretches and the crank flexes with the acceleration load. So actual piston heigth at 6500 rpm is more.

cheers
Rohan

[Craven]

I would check what C/R you will have with that amount of squish much lower than I work with, total around 0.040 is about right with a standard twin cam head.

[ill_will]

Thanks for the replies. I'm hoping the 125E rods will be ok to be honest as I've had them crack tested and honed to the pins. Steel rods at either length would be lighter which is arguably the main advantage of switching I guess, unless the engine is accidently overreved.

Is there a guide minimum head to piston clearance figure that you work to? I have 0.060" in mind for crank to block (and iirc valve to piston, but don't have my notes to hand) but it must be quite a bit less than that in many cases.

I will need to cc the head once the valves are fitted to work out possible CRs and gasket options. I wasn't able to find a ballpark figure for the SAS race spec head last time I looked.

[rgh0]

I generally target 50 thou mininum head to pistons deck clearance. This is made up of 20 thou piston deck below block and 30 thou compressed gasket clearance. The piston cut outs to valve clearance going over top dead centre also need checking and I aim for around the same number on depth of valve head to piston valve cut out and around a minimum of 30 thou on clearance of the valve head with the sides of the pockets.

I know my values are conservative and you can probably build it tighter and get away with it...... most of the time


cheers
Rohan

[Craven]

Once you move away from the Lotus design you are in the hands of a small number of followers that have and I guess established safe working parameters for these modified engines.
My engine building is limited to blueprinting standard Big Valve T/C’s where using improvements in materials and machining can bring about a sweet trouble free engine capable of thousands of road miles.

[ill_will]

Some progress.

The (correct) long stroke crank assembly has been dropped off to be balanced with the flywheel etc. I was missing the dowels so had a slight delay whilst getting hold of some.

Excitingly, I now have a head built up and ready to bolt on. Santa came early!