420c phase 2

kevencyr · Post by **kevencyr** » Wed Dec 30, 2015 11:16 am

does somebody know the proper piston compression i should have on a 420c phase 2 production, got the water pump on engine. just about done with the head, would like to check compression before heading fwd. thanks

notmeu · Post by **notmeu** » Wed Dec 30, 2015 12:31 pm

kevencyr, you should be in the 110 psi range, but more important they should be similar in compression, between the 2 cylinders. There is many threads taking about compression. Here is one:
http://www.jdcrawlers.com/messageboard/ ... highlight=

kevencyr · Post by **kevencyr** » Wed Dec 30, 2015 4:46 pm

just found out i need to overhauled my engine, so happy. i got 110psi on #1 and 85 on #2

notmeu · Post by **notmeu** » Wed Dec 30, 2015 5:01 pm

kevencyr wrote:just found out i need to overhauled my engine, so happy. i got 110psi on #1 and 85 on #2

If the machine has been sitting for a while the rings may be stuck. A little pb blaster in the 85 psi cylinder may loosen the ring up a bit and the compression will rise. That's not too terrible of a difference.

kevencyr · Post by **kevencyr** » Wed Dec 30, 2015 5:09 pm

so what would be your suggestion, since i;m there with a brand new overhauled cylinder head, should i do the bottom. if so, where could i get a good overhaul kit. i saw some but there taking about bore size, does that mean i need to oversize my cylinder.

Stan Disbrow · Post by **Stan Disbrow** » Wed Dec 30, 2015 8:02 pm

Hi,

Well, cylinders wear in an hourglass shape, so one has to bore them oversize to make them cylindrical again. If one is lucky, it can be done to the first oversize. If not, then to the second oversize. After that, it usually means a new block.

Stan

gregjo1948 · Post by **gregjo1948** » Thu Dec 31, 2015 4:45 am

I think notmeu has the right idea. If both cylinders were at 85, it should still run. It may start a bit slower but would run OK. Unless there is scoring in the weak cylinder, I would think, they should be closer to the same compression. I'd say, work it a while then, check it again. It won't hurt anything and you may not need to rebuild the cylinders. I know you said you were working on the head but, if the head is cracked or a valve on number 2 isn't seating properly, your compression will be down.

kevencyr · Post by **kevencyr** » Thu Dec 31, 2015 10:16 am

the head has been rebuilt last year, brand new valve seat, valve guide, valve and spring, also pressure tested. the cylinder head is good. but took my gear cover off last night cause my second gear was always disengage when forcing on something. not a good idea, got 4 damage gear and one on a shaft. starting to wonder if its worth it to be fix.

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