07-23-2011, 11:48 PM #1
Help no compression middle cylinder
Went for a ride today wide open engine died when I hit a wave (not a huge one barely came out of the water) just like you pulled the teather off. No compression in middle cylinder. Towed it in and brought it home pulled the head, gasket looked OK Piston looked good. The valves dont look like they are sealing. If you fill them with water 3 of the exhaust valves wont hold water in the runners with no cam installed. You can see light around them from the outside into the runners. I think I have some bent valves.....
1. Where can I get reliable quick head work done
2. How would I bend the valves? I didnt have water in the hull it has a rev limiter that works.
3. Has anyone used the SBT exchange heads? I saw them on there for 500 bucks...
07-23-2011, 11:58 PM #2
I usually use gas and put ontop of the valves and then see how much, and where they are leaking down in the chamber.
It can be slight leakage but over time if you look you will see what valve is leaking and where.
A good valve cut and lapping of valves will fix the issue.
I have pulled my head every year for the last 3 years to have my head tested and cleaned up before each season.
what were your compression numbers as you said you did not have any in the center?
If in fact middle cylinder has 0 compression you have bigger issues that I would do a leakdown test to see where all the comp is going before you tear the motor appart.
Give Erik "speedfreeks" a call and he can fix you up.
He is in NY.
It is very well possible that your head is fine and does not need to be exchanged.
07-24-2011, 09:29 AM #3
Erik is on vacation LOL I called him just before he left to ask about a ride plate mod. I did not have the correct adapter to do a real test for compression, but I can tell you from the finger test I could hold the compression in the cylinder with my finger the other two I could not. I have already pulled the head and the gas test with the cams out so all valves should be closed I took something and bounced each valve so it would seat (which I shouldnt have had to do) and on the exhaust side 3 out of 6 valves wont hold any gas it pours right out. You can litterly see light in the chamber if you hold the light on the outside and look in the exhaust port. The middle cylinder is the worst I can fit my fingernail under one of the valves it is so far open. Piston looks grea cylinder walls look great head gasket looked perfect. That was the only thing I could find that explained the loss of compression.
07-24-2011, 09:18 PM #4
Please I could really use some help with this. I cant understand what caused this? Is this a week spot for these engines? The valves are sticking you can tap them with a hammer and they seem to close better but not 100%. Could the stems be bent? I dont want to get another head and have the same thing happen again. Has anyone ever had good or bad luck with SBT I have heard good and bad about them in the 2 stroke forum. I looked in Jerrys store, but didnt see anything about a head exchane etc?
07-24-2011, 09:24 PM #5
You will not find a lot of positive things about SBT and the 4Tec engine. You might try forum member Slow 91, he has done a lot of head work for several here on the forum.
As you know, Erik at SFR would be a great choice. But he is going to be gone on vacation for another week.
07-24-2011, 09:27 PM #6
07-24-2011, 09:45 PM #7
I sent him a PM thanks guys...
Are the head bolts torqe yield as in you can only use them once?
The head gasket is metal. Can you reuse do you recommend to reuse? I think I should just get a new one, but at almost 90 bucks I thought they might be OK to reuse.
07-25-2011, 01:09 AM #8
07-25-2011, 07:11 AM #9
Get arp head bolts you can retorqe them anytime Never I repeat never reuse head bolts.
07-25-2011, 10:02 AM #10
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