Engine Knock

[JLowe18]

I am in need of some help. I have a sealed 1250 that came in my car when I bought it and I do not know the number of races it has had since it was rebuilt. Since I have had it I have raced it approximately 10 times. I had it resealed back in December by USLC and recently put it back into my car to prepare for the upcoming race season. I changed the oil, started the car up and everything semed fine. I have started the car a couple of times since then to work out some electrical gremblins I had. On Wendesday of this week I put a new set of JR9C's in the car, fired it up.Immediately the car began to knock. I have a friend who has built several 1200's that has helped me attempt to diagnose what the issue may be. It sounds like one of the valves is hitting a piston but we have ran a borescope down into the cylinders and don't see any evidence any of the pistons have been hit. We have also taken the valve cover off and verified that all of the valves are moving when we rotate the exhaust cam. There is a point though where the engine feels like it has compression though when we rotate the cam even though all the plugs have been removed. Yesterday we ran a compression test on the engine cold and came up with the following readings: Cylinder 1 140#, Cylinder 2 130#, Cylinder 3 100# & Cylinder 4 140#.

Any idea's for a simple solution before we take it to USLC? If I am going to sink money into my engine program I would rather spend it building a 1200 rather than rebuilding this engine. I just can't understand how an engine ran fine Tuesday night and is knocking Wendesday when all I did was change the plugs.

Thanks in advance for any help you can give me.
Jeramy

[Winterracing]

Put the old plugs back in and see what happens?

Dan

[knoxracing]

There is a VERY good chance you have debris in a cylinder. It is not uncommon to have this happen when changing spark plugs.

[Earnst85]

Anyone thinking maybe the valves need checked & adjusted?

[VMS Motorsports]

There is a VERY good chance you have debris in a cylinder. It is not uncommon to have this happen when changing spark plugs.

+1
Welcome back Dennis.

Were the old plugs JR9C's also?
Definitely would check & set the valves

[Silvertip]

Without taking it to USLC, you can change oil, plugs and carbs -Thats all you're legally a llowed  to do.  Well, I guess you can clean the outside of the engine also but consult the rule book before you do just to be safe - don't want to be caught spraying it off with the wrong length water hose.

Honestly, I would bring the engine to the dark side by tearing it apart,  use what you can from it to build a 1200 and enjoy working on your own engines.  No more probing every orifice of the engine when an issue arises. 

If that suggestion doesn't appeal to you, then could be a valve issue.

[JLowe18]

Thanks for the suggestions. The old plugs were JR9C's. I checked and they seem to be the same legnth as the one's I installed.

I am going to look into adjusting the valves in the morning. Hopefully that will do the trick.

[justfreaky]

Without taking it to USLC, you can change oil, plugs and carbs -Thats all you're legally a llowed  to do.  Well, I guess you can clean the outside of the engine also but consult the rule book before you do just to be safe - don't want to be caught spraying it off with the wrong length water hose.

Honestly, I would bring the engine to the dark side by tearing it apart,  use what you can from it to build a 1200 and enjoy working on your own engines.  No more probing every orifice of the engine when an issue arises. 

If that suggestion doesn't appeal to you, then could be a valve issue.

While I get your arguement; You are not entirely correct. Read your rule book.
The hose thing.... VERY FUNNY!!!!!!!!

Steve

[VMS Motorsports]

Exhaust leak!
Check your exhaust gaskets or for a stripped stud

[Richie25x]

Exhaust leak!
Check your exhaust gaskets or for a stripped stud

Check in to this. Kevin Yettes had this problem.  His motor was making a knock/tick sound.
Turned out his headers were bad. he replaced headers and new header gaskets noise was gone.

[stuart anderson]

little rocks in the plug hole is a possibility but then you blew compressed air at the plugs as you removed them, right?
What's of concern is all the cyls show low compression.  100psi after ten or 17 pumps WOT is unacceptable.  And the 140's not much good ether.
An exhaust leak can sound like a knock.
Drain the oil and look for metal flake, and of course all that black plastic.  )
A valve check and adjustment is appropriate in a hope to address the compression issue,  and I'd torque the head.  A blowing head gasket will squeek or make popping noises, on start up at first.
   If it's of interest, I have a XJR 1188 engine I'm offering for sale.
   It was to do service in a Baby Grand on local road circuits.  Never really made it to race, as the car was wrecked during practice for it’s first race.  The engine has perhaps 6 hours on it, with one + of those hours, being several non load, heat cycle / oil change / head torque / check valve lash, low RPM “let the parts get friendly” heating cooling sessions.  The other 4-5 hours being two driver schools.  Mostly follow the leader 20 minute sessions with talk in-between.   So it’s basically brand new.  Priced to sell.  Comes on one of my nice engine stands.
Stuart Anderson
Psycle Racing
770-457-0538  You have to leave a message and I'll call you back.

 

[JLowe18]

Thanks to everyone for all the good suggestions. Unfortunately I learned a hard lesson here recently . I have found the source of the knock. It was a very small screw. I run two fans above the head to provide cooling to the head. At some point last season one of the screws that hold the electric motor's to the fans backed out of the motor. I made an assumption that it just fell out onto the track somewhere. Lo and behold when the head was pulled there was my screw. Evidently it was hanging out on top of the head waiting for a chance to fall into the head and when I removed the plugs in it went.

The guys at USLC got me all fixed up again. As it turns out I had a broken intake cam that I did not know about. If I didn't have this minor problem it could have turned into a major problem later on. I guess that's the silver lining to my problem.

Thanks again to everyone for their  help. This forum is a great resource.

Jeramy

[IraceLegends77]

If you had a broken cam you would have known.

[knoxracing]

No you could easily have a cracked cam and it operate fine, this one was caught in time. 
I suspected you had something fall in the plug hole when changing plugs. I hate when asked to pump an engine at a race track and this is exactly why. Always blow the area out with compressed air, even at the track if you can. I am glad you were able to get it taken care of.

[VMS Motorsports]

Cracked cam could not have shown any issues, broken cam would of. Scott was probably taking the OP's statement of "broken" literally, not interpreting it as cracked.

Glad you got it taken care of Jeramy.