cylinder length

[hrc43]

hi can anyone tell me the height of a 4lo cylinder.i have a rattle from the top end which has disappeared after i gradually fitted more base gaskets .i started with 1 then 3 then 5 and now the noise as virtually gone
the pistons were flush with the top of the cylinder and there was a 2mm squish with one gasket.i am not sure if the cylinders have been skimmed or the compression was too high causing the noise .also does anyone know the head volumes for a standard 4lo.some one told me they thought the pistons sat lower in the cylinder than they do on mine.with one gasket the bottom of the transfer ports are flush with the top of the piston which looks right to me. cheers

[winnerevo1]

Are the barrels on a high over bore? If so is the bore in the gasket big enough for the oversize pistons because gasket bores are only 65.00mm.

[hrc43]

they were on 1.5 then 1.75 then 2mm and the rattle stayed the same but the base gasket size shouldn't change should it?only the head gasket.

[winnerevo1]

I mean the bore in the head gasket. What bore size is the cylinder/piston?

[hrc43]

ah im with you.the standard head gasket was bored out to miss the piston i have even tried a pattern gasket with the metal ring taken out just to see if it made a difference cheers

[winnerevo1]

Ahh,ok thought maybe the pistons were hitting the head gasket.

I'll have a look at a motor tomorrow & measure a barrel height because I'm not sure myself.

[hrc43]

thanks

[winnerevo1]

Had a quick check, the outside edge of the piston is indeed flush with the top barrel face. Measured a couple of barrels from different sets and the length from base to head gasket surface of a bare barrel is 102.5mm.

I can't help with the chamber volume other than the specified C.R is 6.2:1. I guess I should've measured the cylinder head thickness so you could check to see if your head has been skimmed, but didn't think at the time. Can do that tomorrow if you want.

HTH.

[hrc43]

thats great i'll take my cylinders off and check them .it may be the head volume thats too low it looks like it has had some work done but without one to compare it with its hard to tell.thanks

[hrc43]

i have measured my cylinders and they are 102.5mm so it must be the head.it measures 46mm from bolt face to gasket face it looks like it has had some work but it is years since i have seen a standard one so its all a distant memory .it looks way too high compression to me and the squish looks really wide concentrating the combustion in to the middle .if the ratio is 6.2-1 does that mean 175cc (1cylinder)divided by 6.2=28cc head volume? or are my maths gone to shit.here are some pics.cheers

[hrc43]

Attachment Deleted

[winnerevo1]

The dome doesn't look standard, you're right that the squish band looks wide.

I don't think that volume calc. is right. Firstly total cc is 347cc but I think you'd have to allow for the head gasket thicknes & bore to be able to calculate chamber volume from the CR though I'm not completely sure.

I'd be interested to know the dome volume of a standard head too. Best way would be to cc a standard head then cc yours.

[ianr4863]

That looks like it might be a Stan Stevens proddie head as pictured in Classic Motorcycle Mechanics September issue

[winnerevo1]

Here you go, 21cc

www.rd350lc.net/Speceng4L0-1.jpg

[hrc43]

need to brush up on my french/belgium/spanish wot ever that is but i think it says its 21cc head volume i'll get myself a pipet tomorrow and check it thanks for the info .i wouldn't think the extra compression would cause the noise but i tried two head gaskets tonight and it was a lot quieter ,maybe this head was run on avgas, when i got the motor it had a drilled sump plug so as obviously had a checkered past, still it runs perfect but is mega noisy

[winnerevo1]

Oct 9, 2013 23:17:59 GMT 1 hrc43 said:

need to brush up on my french/belgium/spanish wot ever that is but i think it says its 21cc head volume

Ha, it says combustion chamber volume: 21cc

(volume de la chambre de combustion) directly translated as: volume of the chamber of combustion.

[hrc43]

i have just had the head volumes measured and they are 14cc but that is without the head gasket using a flat plate which does not take into account the dome on the piston or the 1.5mm gasket thickness .i know it is a long shot but does anyone know what the head volume should be as i have had it measured or if this should be 21cc or know where i can get a profile of the combustion chamber shape.hurry im holding my breathe

[winnerevo1]

I would've said it should be 21cc as you've measured it or close to it. 14cc sounds way too small to me.

[muttsnuts]

the 21cc's is the combustion chamber size on the head only, so your's is a 3rd smaller, so it could be "dieseling" which would cause like a metallic sound when the engine is running, when measuring the overall cubic capcity and compression ratio you need to factor in a good number of things, the typical ones are;

1. Stroke
2. Bore
3. Combustion chamber size (cc's)
4. Head gasket thickness
5. Deck height (this is the distance between the edge of the piston and the top of the cylinder block, typically 0.5mm)
6. Piston dome shape (you need to measure both the positive and negative values to determine the CC's)

Once you have all of that then you can work out your CR etc

Be aware that small amounts of variances can make a huge difference to CR (Combustion ratio), as an example an engine I was looking at the other day, just a variance of 0.5mm on the head gasket thickness changed the CR by one full point, so it went from 13:1 to 14:1

Also, you should note that a genuine Yamaha gasket is a lot thicker than the pattern ones, also if you run an "O" ring head then the CR goes up quiet a lot.

HTH

[hrc43]

Oct 11, 2013 9:20:24 GMT 1 muttsnuts said:

the 21cc's is the combustion chamber size on the head only, so your's is a 3rd smaller, so it could be "dieseling" which would cause like a metallic sound when the engine is running, when measuring the overall cubic capcity and compression ratio you need to factor in a good number of things, the typical ones are;

1. Stroke
2. Bore
3. Combustion chamber size (cc's)
4. Head gasket thickness
5. Deck height (this is the distance between the edge of the piston and the top of the cylinder block, typically 0.5mm)
6. Piston dome shape (you need to measure both the positive and negative values to determine the CC's)

Once you have all of that then you can work out your CR etc

Be aware that small amounts of variances can make a huge difference to CR (Combustion ratio), as an example an engine I was looking at the other day, just a variance of 0.5mm on the head gasket thickness changed the CR by one full point, so it went from 13:1 to 14:1

Also, you should note that a genuine Yamaha gasket is a lot thicker than the pattern ones, also if you run an "O" ring head then the CR goes up quiet a lot.

HTH

thanks for that ,just when i thought i was getting to understand it .
i am having the heads remachined to 22cc with a 1mm squish and oring's in the top of the cylinder' its on 2mm oversize so is a bit more than 350.hope this cures it .it does sound like what you describe with the metallic noise i thought when i took the heads off there would be bits of bearing floating round but no. then after 2 cranks 2 rebores and all the gearbox bearing replaced it was still the same so fingers crossed