Well been tinkering with my engine. Twinport 1600 single carb, all winter as I’ve not been happy with the way it has been running. All this started with a misfire last summer. I’ve replaced plugs, leads, rotor arm, fuel pump, fuel lines, put on a malpassi fuel regulator, set valves, timing, tried to tune the carb but not sure I’ve got it right (it’s an empi 34 3). Anyway decided to try a compression test and 1 = 130 2= 105 3= 145 But 4 = 90 I squirted oil down 4 and it hardly moved. I also have various oil leaks, flywheel seal I think, oil pump cover, push rod tubes and possibly case bolts. I replaced the rocker covers and bail arms with Scat ones which seems to have solved the rocker cover leaks. I was building up to pulling the engine to resolve the leaks but now concerned about the compression. Any ideas? Is this as bad as I think it is?
Yes... if its too tight , should set them before a comp test to make sure ;-) canb) also help tell if its more likely valve issue or rings... Sent from my SM-T580 using Tapatalk
Fingers crossed it is. Tools away for today but will measure the valve clearances again tomorrow evening. Really hope it is just that. Cheers
being tight might also be an indication your valve is stretching which is bad.... Sent from my SM-T580 using Tapatalk
I remember messing up no 4 up when doing it and having to start again so it may very well be that. Will also check the others especially no 2 as that also seems low. Hoping the Valve isn’t stretching as Deefer66 says. At least I’m learning my way round engine just don’t think I’m ready to challenge myself with a rebuild just yet. Clock is ticking though first site of the season booked for May!
I'm sure it's a bit lumpy / shakey at idle and not purring like a smooth thing? If setting the valves cures that and the cranking psi you could wait and see if the idle get's lumpy again. If it happened in a few hundred miles I would take action. If it doesn't happen at all you'll know it was a valve setting error. If it took 1,000 miles you'd probably have time to
That's my experience ^ closed up or nearly at normal service, 1,000 miles, 200 miles, 25 miles, give up and count myself lucky I didn't wreck it/slap myself for risking it.
Yep, it is certainly lumpy and shaky at idle. Thought it was the carb and my inability to tune it correctly. I’ll run through the full check again, valves, timing and carb. If it is not the valve clearance I’ll be in inconsolable especially this close to the world opening back up again.
Tappets are better on the slightly loose side rather than snug , too tight and it'll burn out the valve . As for the slightly lower compression on one cylinder, if the valves gaps are ok and it ain't broke - go camping Sent from my SM-G960F using Tapatalk
IME, it might improve a lot but not completely, if this is actually the problem, because as lasty says, if completely closed up, the valve won't have been sealing properly. Another check would be to remove the rockers and put a straight edge across the valve stems. If you have a receding valve seat, it's stem will stick out further. On the bright side, it's not a huge task in terms of mechanical engine failures, it's one you can fix by replacing almost the very first part you take off (rockers first), it doesn't fill the case with filings and shrapnel and it gives you plenty of warning if you're paying attention as you were. .
I may have identified the problem and I’m a bit less concerned now although not sure how to solve it. So I checked the valve clearances and they all seemed roughly ok apart from the exhaust valve on no 2. Ran the compression test again but this time got; 1 - 131 last time 130 2 - 150 last time 105 (don’t believe I recorded it incorrectly first time round) 3 - 145 last time 145 4 - 89 last time 90 So having a rethink I realised the tester on no 4 only took 1 1/2 turns, if that, to go in. Took it out and tried again but it still wouldn’t seat properly or the same as the others. So this time rather than cranking myself and then coming back to check the results I asked the Mrs to crank it and I held the tester in place. It immediately went up to 110 but was also pushing air out around the fitting. So whilst a spark plug will go in no 4 with no issues I think it is cross threaded hence the reason the tester won’t seat properly and gives an incorrect reading. I’m happy that my compression is not below 100 when held so might have avoided a top end rebuild but should I worry about the plug hole being cross threaded? Also need to figure out why it is idling all lumpy and my spark plugs are fouling. Not sure I have the mixture on the carb right. Might give it a good run this weekend if it is willing.
Cross threaded spark plug is never good and if it’s not seating properly your going to get compression loss. Probably not easy to see but you could spray wd40 or something like at the base of the plug to see if it’s leaking when running. Plugs will be sooty if it’s not been warmed up and had a proper run at operating temperature.
Does the sparkplug thread look the same as the others If the heads been damaged in the past it could of been helicoiled and it’s unscrewing with the spark plug
Yep I’ve had it idling a lot while working on it so probably not getting up to temp. The bizarre thing is the spark plug goes in just fine but will try the the WD40 trick.
The spark plug is the same as the others it is just the tester I couldn’t get to thread properly. No 4 is the easiest one to get to as well so it should have been the easiest.
Are the threads ok on the comp tester? They never tend to screw in far only a few threads on the adapter. Also possibly carbon build up on the head plug threads.
Yep think so. It went into the others okay. Carbon build up is a possibility will try and get a look down there if I can.
