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squish
Feb 12, 2017 11:22:04 GMT 1
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Post by plumma on Feb 12, 2017 11:22:04 GMT 1
I have a 421cc with a o-ringed head and I measured the squish today and it was at 0.72mm or about 29 thou. Wondering what people think?
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squish
Feb 12, 2017 11:55:48 GMT 1
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Post by lrcarl on Feb 12, 2017 11:55:48 GMT 1
Using stock cylinders +4 crank on mine 0.9 optimal 1/1.2 ok for road use was advise from tuner Carl
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squish
Feb 12, 2017 16:22:26 GMT 1
Post by Tobyjugs on Feb 12, 2017 16:22:26 GMT 1
Squish is only half the story make sure you have enough volume or a compression ratio around 12.5:1. Both need to be good.
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squish
Feb 12, 2017 21:21:37 GMT 1
Post by wallcraft on Feb 12, 2017 21:21:37 GMT 1
I have a 421cc with a o-ringed head and I measured the squish today and it was at 0.72mm or about 29 thou. Wondering what people think? I'd say that's to tight, as said 1mm-1.2mm for serious road thrashing.
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squish
Feb 12, 2017 21:32:05 GMT 1
Post by 4l04ever on Feb 12, 2017 21:32:05 GMT 1
My LC gets a lot of thrashing and the squish is 0.95mm.....
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squish
Feb 13, 2017 4:24:32 GMT 1
Post by bare on Feb 13, 2017 4:24:32 GMT 1
I have a 421cc with a o-ringed head and I measured the squish today and it was at 0.72mm or about 29 thou. Wondering what people think? Fair chance that the piston may hit the head. Tolerances add up and all of a sudden.. metal bits collide.
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squish
Feb 13, 2017 6:54:24 GMT 1
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Post by plumma on Feb 13, 2017 6:54:24 GMT 1
New domes are in order
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squish
Feb 13, 2017 10:03:00 GMT 1
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Post by lrcarl on Feb 13, 2017 10:03:00 GMT 1
O.3 thicker base gasget might be cheaper Carl
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squish
Feb 14, 2017 0:19:49 GMT 1
Post by 4l04ever on Feb 14, 2017 0:19:49 GMT 1
Yes, thicker base gaskets is the way to go.
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squish
Feb 14, 2017 3:55:53 GMT 1
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Post by plumma on Feb 14, 2017 3:55:53 GMT 1
Base gasket is the go then
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squish
Feb 14, 2017 10:43:29 GMT 1
Post by Tobyjugs on Feb 14, 2017 10:43:29 GMT 1
Base gasket is the go then If your squish is wrong i think you should also check your compression ratio as they go hand in hand. If the compression ratio is good then just adjust with base gasket as 0.3mm does not change your port timing enough for you to notice. Also the profile of the piston crown can be misleading compared to your head. It will be easy to measure the compression ratio as you have an O-ringed head. If you're not sure how to do this i will write it up for you.
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squish
Feb 14, 2017 16:58:43 GMT 1
Post by muttsnuts on Feb 14, 2017 16:58:43 GMT 1
Which head is fitted, I am assuming your probably running 21cc domes, either way that squish is too small on a 421, and with the pistons being cast ones, you also need to factor in piston rock otherwise you will smash pistons, normally on the inlet side.
Your head will have removable domes, so you can easily machine them to give the squish you need. I recommend running 1.2mm for road use and thus far on mine I've covered nearly 1000 miles since setting mine at 1.2mm with no issues
HTH
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Mad Biker
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We lead others try and follow.
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squish
Feb 14, 2017 19:28:15 GMT 1
Post by Mad Biker on Feb 14, 2017 19:28:15 GMT 1
Before you go ahead and get a different thickness base gasket, its worth checking your original gasket has not compressed over time if you have done a few miles / or you have had the cylinders on and off a few times. Ive seem gaskets compress by 0.3 overtime. once the cylinders come off i fit a new gasket and check squish as a matter of course, even if it is going back together as the same spec.
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Post by muttsnuts on Feb 14, 2017 19:52:20 GMT 1
agree, always check the squish on these and I always fit a new base gasket because of exactly what Martin says, they do compress down further if you use them more than once
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squish
Feb 14, 2017 20:48:20 GMT 1
Post by jon on Feb 14, 2017 20:48:20 GMT 1
This is exactly why simple maths are not real world in this case.
In theory an engine with next to no squish if fine IF the compression ratio is correct.
The reason most people run 1mm+ is because of the real world. Gaskets reduce thickness over time de to the forces. Think about a new build and tightening the head nuts to the correct torque after use. Bearings have minimal tolerances as they wear, and pistons expand with heat.
That is why 1mm/+ is recommended to allow for this.
I once saw a lambretta head optimised for as little squish as possible on a race engine. The piston had a tiny raised number to denote the oversize. This was neatly stamped into the head after use.
Jon
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squish
Feb 15, 2017 3:33:16 GMT 1
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Post by plumma on Feb 15, 2017 3:33:16 GMT 1
I purchased the bike/engine as a project, bike is a ypvs frame, rgv front and rear with R6 sub frame and tank. Engine is a 421 with Athena top. Engine has never been started and I was unimpressed with Athena head, no thermostat and different water outlet so I decided to purchase a wicked motorsport torque head. It had 21cc domes and have no idea of comp ratio. Electrical system is a mix of lc loom and ypvs stator and cdi.
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squish
Feb 15, 2017 3:35:26 GMT 1
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Post by plumma on Feb 15, 2017 3:35:26 GMT 1
Which head is fitted, I am assuming your probably running 21cc domes, either way that squish is too small on a 421, and with the pistons being cast ones, you also need to factor in piston rock otherwise you will smash pistons, normally on the inlet side. Your head will have removable domes, so you can easily machine them to give the squish you need. I recommend running 1.2mm for road use and thus far on mine I've covered nearly 1000 miles since setting mine at 1.2mm with no issues HTH That would be great!
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squish
Feb 15, 2017 3:36:25 GMT 1
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Post by plumma on Feb 15, 2017 3:36:25 GMT 1
Base gasket is the go then If your squish is wrong i think you should also check your compression ratio as they go hand in hand. If the compression ratio is good then just adjust with base gasket as 0.3mm does not change your port timing enough for you to notice. Also the profile of the piston crown can be misleading compared to your head. It will be easy to measure the compression ratio as you have an O-ringed head. If you're not sure how to do this i will write it up for you. This would be great!
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squish
Feb 18, 2017 0:47:46 GMT 1
Post by Tobyjugs on Feb 18, 2017 0:47:46 GMT 1
There are two types of compression ratio but the one i use as a guide is good enough for checks to make sure the basics are good.
You need to know the volume that your piston moves and the volume that still exists above your piston if it is at TDC
The volume your piston moves is 3.14(pie) X piston radius (68mm piston has a radius of 34mm) Squared X stroke of crankshaft (standard 54mm +4mm big bore) This is 3.14 x 1156 x 58 = 210530.72 cubic millimeters which equals 21.05 centiliters
The second part you need to know is the volume above your piston. First remove your head and put a thin smear of grease on the barrel surface so that when the engine is turned to TDC the grease coats the piston ring making a good seal. put your head back on and lightly fasten the head. With the piston in tdc fill up the combustion space with oil using a graduated syringe. Take note of how much oil you have used to fill the space up untii the oil level is flush with the top of the spark plug hole.
Note this in centiliters then subract 2.2 centiliters for the volume taken up by the spark plug. so we measured 4 centiliters this means 4 - 2.2 = 1.8 centiliters volume
you now add both volumes together and then divide the answer by the volume measured above the piston at tdc. 21.05 + 1.8 = 22.8 divide by 1.8 = 12.7
The 12.7 is your compression ratio
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chrisk
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squish
Feb 18, 2017 1:13:06 GMT 1
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Post by chrisk on Feb 18, 2017 1:13:06 GMT 1
Worth mentioning imo.
Always worth dowelling/pinning the head to cylinders. Best done when cases are split.
It's amazing how far off the chambers can be with the head floating about, and cylinders in the case of lc's and rd.
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squish
Feb 18, 2017 3:51:43 GMT 1
Post by bare on Feb 18, 2017 3:51:43 GMT 1
Why? the sleeved head nuts do a decent job of centralising the cyl head on to studs.. as is.
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squish
Feb 18, 2017 9:11:14 GMT 1
Post by jon on Feb 18, 2017 9:11:14 GMT 1
There are two types of compression ratio but the one i use as a guide is good enough for checks to make sure the basics are good. You need to know the volume that your piston moves and the volume that still exists above your piston if it is at TDC The volume your piston moves is 3.14(pie) X piston radius (68mm piston has a radius of 34mm) Squared X stroke of crankshaft (standard 54mm +4mm big bore) This is 3.14 x 1156 x 58 = 210530.72 cubic millimeters which equals 21.05 centiliters The second part you need to know is the volume above your piston. First remove your head and put a thin smear of grease on the barrel surface so that when the engine is turned to TDC the grease coats the piston ring making a good seal. put your head back on and lightly fasten the head. With the piston in tdc fill up the combustion space with oil using a graduated syringe. Take note of how much oil you have used to fill the space up untii the oil level is flush with the top of the spark plug hole. Note this in centiliters then subract 2.2 centiliters for the volume taken up by the spark plug. so we measured 4 centiliters this means 4 - 2.2 = 1.8 centiliters volume you now add both volumes together and then divide the answer by the volume measured above the piston at tdc. 21.05 + 1.8 = 22.8 divide by 1.8 = 12.7 The 12.7 is your compression ratio Tobyjugs, I'm interested to understand how you came up with the spark plug volume? Surely machining tolerances and skimmed heads effect this. Also once the plug is fitted does this reduce volume? I only ask because being near the size of the head volume small inaccuracies could make a big difference. Also even with expansions doesn't some of the compression that could have been built up leak out the exhaust port before closing. I understand at that point the pressure is still low and the reverse wave tries to push back in, but not all surely? Good advice to measure it accurately though. There is no point using a generic dome size, as it depends on displacement too. I've seen it done before with the head level and inverted with the plug fitted. Oil is then introduce from a syringe and measured. To make this more accurate a perplex plate with a filling hole can be place on the head so the oil miniscous doesn't effect the reading. The piston BTDC and dome can be worked out mathematically which is usually accurate enough. In fact it's hot mme thinking if cancels its self out, where the piston crown protrudes the gasket face, while the piston edges sit slightly down??? Perhaps I'll measure so day, Jon
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squish
Feb 18, 2017 12:40:20 GMT 1
Post by Tobyjugs on Feb 18, 2017 12:40:20 GMT 1
Hi Jon i will try to answer your questions as best i can, don't forget i am an enthusiast and only understand some of the basic's so i can build my engines up correctly.
Q; Tobyjugs, I'm interested to understand how you came up with the spark plug volume? Surely machining tolerances and skimmed heads effect this. Also once the plug is fitted does this reduce volume? I only ask because being near the size of the head volume small inaccuracies could make a big difference.
A; The spark plug is made to a specific design. The thread, electrode and porcelain all screws into the cylinder head until the sealing ring on the plug tightens up onto the head. Because we have filled the combustion space with liquid until the very top of the spark plug hole if you screw the plug in it will displace the liquid as liquid does not compress. This will always be the same if you screw the plug all the way in without any spacers or extra rings added to the plug. This amount of space taken up by the plug is roughly 2.2 cl.
Q; Also even with expansions doesn't some of the compression that could have been built up leak out the exhaust port before closing. I understand at that point the pressure is still low and the reverse wave tries to push back in, but not all surely?
A; your right there are a lot of things going on when its working. My tip or guide is only for checking that the basic configuration is correct. I have tried to explain is called uncorrected compression ratio. You also have corrected compression ratio which i don't fully understand and that is for the tuner.
Q; Good advice to measure it accurately though. There is no point using a generic dome size, as it depends on displacement too.
A; There are lots of people out there selling parts for these engines with a plug and play vibe. You have passionate people like Norbo and MBD who want to do there best and you have people that want to sell and make money without too much hassle. It does not always work out as plumma noticed. I have also had the some misfortune from blindly trusting the work done to my cylinder head by a famous tuner who lives close to you and a company famous for making swing arms. My engine was pinking and further investigation led to a compression ratio of 16:1 which is a bit high for 400cc road engine. My advice is only for checking.
Q; In fact it's hot mme thinking if cancels its self out, where the piston crown protrudes the gasket face, while the piston edges sit slightly down??? Perhaps I'll measure so day.
A; The volume moved by the piston will always be the same no matter what profile the piston crown is and the space left over in the combustion area is very easy to measure using fluid. I don't think i would be able to calculate it mathematicay unless i had a couple of days.
Checking the compression ratio is now on my list of routine checks i do whilst building an engine up if it has been modified since last checking or an engine which is opened and built up by me for the first time I write the info in a book with the engine number for later reference.
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squish
Feb 18, 2017 17:46:43 GMT 1
Post by bare on Feb 18, 2017 17:46:43 GMT 1
Don't forget that Yama San gave us head gaskets comprised of 3 stamped metal leaves of differing thicknesses. Mix'n match those leaves (adding OR subtracting ) to ; a) optimize squish b) Alter(fine tune?) compression Use a comp gauge: less than 100 psi = rebuild, while 150 or more ..Also ..equals imminent rebuild :-)
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squish
Feb 18, 2017 18:21:56 GMT 1
Post by davecroucher57v on Feb 18, 2017 18:21:56 GMT 1
bare it is 68mm.
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squish
Feb 18, 2017 18:23:23 GMT 1
Post by davecroucher57v on Feb 18, 2017 18:23:23 GMT 1
bare it is 68mm.
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squish
Feb 18, 2017 18:27:33 GMT 1
Post by davecroucher57v on Feb 18, 2017 18:27:33 GMT 1
ended up at 23.5 vol 1.2 squish 10.5 ring = 152/154 comp.
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chrisk
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squish
Feb 18, 2017 18:54:34 GMT 1
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Post by chrisk on Feb 18, 2017 18:54:34 GMT 1
Why? the sleeved head nuts do a decent job of centralising the cyl head on to studs.. as is. Hi..not always the case from what I have seen. If you pop a pv head on a loose barrel, have a look at how much out of central it may be when you move it about. Sometimes you can be lucky and note that simply pushing in one direction on the head lines everything up. With p valves obviously the barrels really need to be on the top case due to the dowels used. And also the dia of squish on a pv is only 64.5, so with 65.5 bores and the sloppy head it is easy to have 1.5 -2mm of head surface over the piston. Plus your squish generally gets a tad closer on rebores. Some heads cannot be lined up easily due to the dowelled barrels, but a good compromise can be made. It can even be just a couple of stud holes in the head, and simply opening them out a little allows the head to align better. Which will help in setting an equal squish.
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Post by bare on Feb 19, 2017 5:48:51 GMT 1
Two points: 150 psi comp IS in the Danger zone.. Feeling Lucky?? Yess the Sleeved nuts ..do... a Fair to good job of centralising the head. But Hey! feel free to 'improve' on what you presume needs improving. Y ama San moved on a bit, since he made the RD 400 setups :-)
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chrisk
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squish
Feb 19, 2017 8:56:25 GMT 1
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Post by chrisk on Feb 19, 2017 8:56:25 GMT 1
Hi bare...its the studs that can restrict alignment.. and help if lucky.
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