Mezz/// Posted January 3, 2012 Report Share Posted January 3, 2012 4k block with a 5k head in my Rolland. I took the head off the block a week ago to port and polish the head etc. When I took this head into the shop,the man said it is a 5k because it has small combustion chambers. Ok so from what I have heard,the compression this would be making may be WAAAAYY to high? QUESTION: WHY DIDN'T MY ENGINE RUN LIKE A DOG? IT DIDN'T EVEN HAVE THAT BARK TO IT LIKE A HIGH COMP ENGINE,AND IT DIDN'T SLOW THE ENGINE FAST WHEN OFF THE ACCELERATOR (like my old 4 with 3k head used to do.. WHY IS THIS ENGINE RUNNING FINE? Is there some way that the cam,or over sized bore and pistons are lowering the compression enough? Ok so my specs are: The crank wheel,when all pistons are at TDC,the crank pulley has the 0 mark about 9 o'clock in reference to the TDC on the block...could this be why?? *Lumpy as cam,very lumpy and boggy down low,unknown cam grind,..much to my disgust... *2 inch exhaust *ported and polished head by myself (guy at machine shop says he was au rises how good it was from me being a novice,..took me 30 hours. *matched the ports to Manifold *40 thou over sized pistons ( so it's bored out slightly) FLAT TOP" *5k dizzy *extractors *Weber *normal head gasket *standard valves I JUST DO NOT KNOW THE ANSWERS???? HEEEEEELLLLLLLLLLLLLLLPPPP PLZZZ GUYZ :)}{ :( Mezz/// Link to comment Share on other sites More sharing options...
Mezz/// Posted January 3, 2012 Author Report Share Posted January 3, 2012 ROLLA I MEANT...iPad has stupid auto correct Link to comment Share on other sites More sharing options...
Mezz/// Posted January 3, 2012 Author Report Share Posted January 3, 2012 Guy at machine shop was surprised how good the port job was....** Lucky I didn't say how surprised he was that I did a good head job,..this would be WAAAAYY wrong from what I'm trying to say,..sheeesh Link to comment Share on other sites More sharing options...
Teddy Posted January 3, 2012 Report Share Posted January 3, 2012 mumma-mia, my eyes hurt. I'm going to look at this again in the morning. Link to comment Share on other sites More sharing options...
trd Posted January 3, 2012 Report Share Posted January 3, 2012 4K's can have both types of combustion chambers. And your got the wrong crank pully for your timing cover. Late model 4k's and 5k's have the timing mark in a different place. Link to comment Share on other sites More sharing options...
philbey Posted January 3, 2012 Report Share Posted January 3, 2012 (edited) Dude knock it off with the capitals. And edit your previous post, don't re post, it's called bumping. And read the forum rules before you break any more. No point wasting everyone's time speculating. As mentioned there are dished 4k motors. The one and only way to solve this is to measure the volume of the head and the piston dish and calculate comp ratio. Edited January 3, 2012 by philbey Link to comment Share on other sites More sharing options...
Mezz/// Posted January 3, 2012 Author Report Share Posted January 3, 2012 Ok,..no worries. I'm new here. Link to comment Share on other sites More sharing options...
Twinky Posted January 3, 2012 Report Share Posted January 3, 2012 If it's running fine who cares right? Id be happy if my engine was running fine... I wouldn't even touch the crank pulley if everything is working fine. Don't rock the apple cart! Link to comment Share on other sites More sharing options...
altezzaclub Posted January 3, 2012 Report Share Posted January 3, 2012 (edited) Yeah slow down a bit Mezz! Philbey and Twinky are both dead right- if you want to know what specs you have you will have to measure the combustion chamber volume with a burette or pipette. That will give you a static compression ratio. Then that is reduced by your porting/carbs and camshaft overlap to give you a dynamic ratio, which is what you measure with a compression gauge. So although you have high compression in theory at idle the cam is bleeding it all away and it only ups the compression at higher revs. If you're not really worried about WHY it goes like it does, just tidy it up and run it the same, as Twinky reckons. If its going well don't mess with it! Did you buy the car with that motor, or just buy the motor?? Can you ask the guy who built it what he did?? Oh- check the back of the cam for numbers and post them up. Most cam grinders stamp them with a code. Edited January 3, 2012 by altezzaclub Link to comment Share on other sites More sharing options...
styler Posted January 4, 2012 Report Share Posted January 4, 2012 (edited) So you want to know why your engine runs fine? Static compression ratios are calculated as if the valves are never open during the engine compression stroke, so in theory only and are used to match camshafts to compression easily when building an engine. Dynamic compression is what the real compression actually is with valves opening and closing during engine cycles and also considering overlap when both valves are open at once and the exhaust scavenges the intake charge. The longer the valves are open and the more overlap the more compression is lost. Generally most older 4 stroke petrol engines would run around 8:1 compression on 90RON and not ping during operation. So for a rough example: Camshaft:---Static:---Dynamic: 260 deg-------8:1---------8:1 270 deg-------9:1---------8:1 280 deg-------10:1--------8:1 290 deg-------11:1--------8:1 300 deg-------12:1--------8:1 Edited January 4, 2012 by styler Link to comment Share on other sites More sharing options...
altezzaclub Posted January 4, 2012 Report Share Posted January 4, 2012 ...and those who voted for Juliar Gilliard have got us forced into ethanol fuel this year unless your local pump has 98octane. Don't use ethanol fuel in two-stroke motors, my head machining shop said. It won't burn quite the same, so compression ratios can all be altered. Link to comment Share on other sites More sharing options...
Hiro Protagonist Posted January 4, 2012 Report Share Posted January 4, 2012 ...and those who voted for Juliar Gilliard have got us forced into ethanol fuel this year unless your local pump has 98octane. 95 is still ethanol-free... Link to comment Share on other sites More sharing options...
SLO-030 Posted January 4, 2012 Report Share Posted January 4, 2012 ...and those who voted for Juliar Gilliard have got us forced into ethanol fuel this year unless your local pump has 98octane. Don't use ethanol fuel in two-stroke motors, my head machining shop said. It won't burn quite the same, so compression ratios can all be altered. We had so many seized 2 stroke motors come into the workshop i did school holiday work. A LOT! we due to ethanol fuel issues. Link to comment Share on other sites More sharing options...
altezzaclub Posted January 4, 2012 Report Share Posted January 4, 2012 95 is still ethanol-free... Ah, OK I take it back. The local 95 I buy has ethanol in, but maybe other brands don't have. I haven't pinned down anything on the Altezza, apart from that my $1000+ head job is due to poor combustion putting soot particles on the valve seats and holding exhaust valves open. I reckon it was one tank of 95octane fuel on a trip back to Orange that caused it, but the fuel company disagree. Link to comment Share on other sites More sharing options...
Mezz/// Posted January 4, 2012 Author Report Share Posted January 4, 2012 Ok so my compression was calculated at over 15.1 compression today by the machinist. He also said that that is way high,..I agreed. so I'm now changing my bottom end,and running a 5k block with dished pistons cam etc. Thank you all for your help. Sorry I was vague with details. I'm going to strip this motor soon,and I will post up the cam to ask if it's suitable for the 5k,assuming they are interchangeable? Does anyone know where I can buy a good 5k bottom end kit from? also,it makes sense that the compression would be different with the valves opening and shutting. I'm going to start posting pics of this ke26 soon,..and the rebuild etc. Thank you all for your time guys.. Looking forward to trying a set up that will be appreciated by onlookers as it's documented for those of us that love the rollas :) Mezz Link to comment Share on other sites More sharing options...
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