alien object - your guess is maybe better than mine!

[el-saturn]

hi there - i?m waiting for my head to get back and thought it?d be nice to give the liners a squirt of oil and while starting at cyl. 4 and moving up i really freaked out when my rubbing index and middle finger "found" these two
imperfections - i didn?t measure the depth of these crevises and would like a few guesses as to how this may have happended (the head overheated and as the follower sleeves revolved a few degrees i thought probably a
chip of one of those sleeves caused this damage??) -------- the bottom is newly put together and the nex question
is WHERE did this chip end up????? and would you also hope it is in the sump: SOUND AND SAFE????? hoping for some creative guesses and alpine greetings sandy PS sketch added

[PeterK]

Gudgeon pin moving in the piston, scratching the bore ?

[oldelanman]

Broken piston ring(s) .....possibly caused by the piston siezing in the bore when your engine overheated ?

[el-saturn]

roger, i hate to have to say thanks, but that could be possible and having a bottom gasket handy and i reckon
it?s worth the time - the head is at a friends shop. ... and timewise an after diner job + -------
i don?t think the liner needs any honing as the last 35mm are still perfect: where or when we need
compression - don?t you agree?? cheers sandy

[tcsoar]

i don?t think the liner needs any honing as the last 35mm are still perfect: where or when we need
compression

The compression is built up through the upward stroke of the piston, and although not at full compression as it passes your marks, I would have thought you may lose some of that compression as the rings pass over them. Not a total loss of compression but certainly a reduction, how much would not be know until back together and a compression test done.

If the marks could be removed with a hone then I think that is what I would do.

Chris.

[rgh0]

I would also do a die penetrant crack check on the mark area as what ever did the damage could also have cracked the bore wall

cheers
Rohan

[ecamiel]

Hi

Be sure to carefully check the wrist pin retaining clips.

Eric
64 S1

[el-saturn]

thanks fellas!! it's gonna be the following: fitting my original 701 which just got honed; using my brand new forged crank, polished and forged rods with my new accralites - these will need machining as i've been told OR use 105octane fuel (not gas station merchandise!!) using the 83,25 (FL111) i was told minus 2mm = 4,25) for a 1:11,5 compression ratio - the head in question is as new (height) and maybe there's a rule of thumb which is applicable?! and maybe some of you have used exactly these parts (hopefully) cheers sandy

[rgh0]

I personally would target 10.5 to 1 if your planning to run normal premium unleaded pump fuel with a 98 or 100 octane compression ratio. I think a calculated 11.5 to 1 is to high unless used with racing fuel or maybe a modern mappable ignition system with knock sensor and maybe an old style long duration racing cam ( which lowers the actual compression ratio)

You need to measure every thing up and calculate the intruder height you need. Including measuring the combustion chamber volume and compressed head gasket thickness and volume of the intruder and volume of the valve cut outs in the pistons. Depending on the rest of the engines detailed dimensions I would expect an intruder in the range of 1mm to 2 mm maximum for a nominal 10.5 to 1

I use an intruder about 4 mm high in an 83.5 mm bore engine to get around 12.5 to 1 compression ratio using 100/130 Octane Avgas. I also open up the combustion chambers somewhat to give better flow around the bigger valves ( 1.625 IN and 1.4 exhaust) this compensates for the volume lost with the bigger valves so their volume is about standard.

cheers
Rohan

[el-saturn]

thanks rohan and i knew there weren?t any shortcuts - my swiss pal and renown engine builder bruno shaffner was saying max 1:11,3 - i did notice that the entire intruder fits into the chamber without gasket and i have 304? cams (10,4 lift intake and 10,6 EX) the intake valves have almost 41mm dia and the ex are 35,5 - if my memory isn?t serving me properly i?ll add the actual dia and lengths tomorrow - you have already been supportive!
aren?t there any drawings which we could follow - i was thinking of getting it done: "hand-made CAD" on my lovely
paralellogramm (very vintage) drawing board. cheers sandy

[cabc26b]

I forget where we started when we cut down the intruders on the pistons , in the end we used a thicker cometic gasket to get to 11.2:1 - vs making the pistons too thin on top.

I also run a blend of pump unleaded 93 octane and leaded race gas to get to 100 octane

[rgh0]

Hi Sandy
With the 304 duration cam ( Cosworth L1?) you can probably get away with a little higher compression ratio than 10.5 to 1 but 11.3 to 1 still sounds a little high for comfort for me on 98 to 100 Octane ( european method ) normal premium unleaded . Personally I would use a shorter 280 degree duration higher lift cam with 10.5 comp ratio as these give better usable road performance I believe.

Yes no short cuts to work out compression ratio and hard to do soley by drawings given the shape of the piston cutouts and head chamber. I measure the volume of the head chambers using a graduated pipette to fill it with kerosene or degreasing liquid, measuring to 0.1 of a cc. The head chamber volume even in an otherwise standard head can vary signifcantly depending on the valve head shape and valve seat location and its worth the effort to get them all equal. I measure the piston intruder and cut out volume the same way but placing it in the bore a set distance from the top of the block, sealing it with a stiff grease between the 2 top rings and then fillling the bore above the piston and measuring the volume and the calculating the net intrusion volume above the piston deck allowing for the valve cutouts and the gap in the side of the piston down to the top ring. The piston deck is the flat top part of the piston around the base of the intruder.

From the above, plus measurement of compressed head gasket thickness and fire ring bore and known stroke and bore and gap from piston deck to block top, you can calculate the compression ratio accurately.

if you do go for a number that turns out to be to high you can always reduce it a little without a total engine rebuild by putting in a thicker custom head gasket.

cheers
Rohan

[el-saturn]

thanks rohan - and as you may presume/know (having a stressy motorsport backround) if you?re ready to compro
mise it immeadiatly becomes measurable - so i have these lovely n.s. (bristol) cams which i?d never change for/in a quick road car as they are perfect - i?m getting rid of my cortina 1600 block (2737 rods) / 1700cc and will use my original block (701) which is newly honed and ready for my new accralites (still with the 1/4inch intruder) and all the other goodies. thanks for all of the info sandy

[SJ Lambert]

Rohan,

Do you have a preferred size/brand of pipette for both measurements?

Cheers

James

[rgh0]

Rohan,

Do you have a preferred size/brand of pipette for both measurements?

Cheers

James

Hi James - I use a 10ml pipette graduated to 0.1ml. Its about 40cm long so easy to use while holding it without a stand.. I will dig it out over the weekend and post a photo. I am still in the process of moving my garage but I think I remember where I put it in all the boxes I have not unpacked yet!

cheers
Rohan