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Need Engine Gurus!!!

10K views 91 replies 23 participants last post by  cheapbastard 
#1 ·
I'm in desperate need of some ideas guys. I built the engine for my T/A racecar (everything new, including the heads) and the first time I fired it up to break the cam in, it ran great for about 8 minutes until it reached operating temp. Then it totally fell on its face and bogged way down so I shut it off. Keep in mind this is idling at 2,000+ rpm with no load. Started it again the next day, did the exact same thing. Turns out, the valve guides were loose in the heads and I had at least 1 exhaust valve stick (1 touched the piston and bent it slightly). So I pulled the whole thing apart, took the heads back to the machine shop who replaced all the guides (cast iron heads) with oversized bronze guides, diamond honed them out slightly larger, replaced the bent valve, new seals, new valve job, etc.



Last night, I finally got it all put back together and started it again. Once again, ran great for a few minutes until it got hot, then fell on its face again and bogged way down until I shut it off (still breaking the cam in at 2,000+ rpm). Then about 4 seconds after I shut it off, I heard what I'm sure was a valve snap shut on the same bank as the one that was bent last time. I pulled the valve cover immediately to check valve lash, and all the closed valves were still in spec. The motor has about 20 min total run time on it. I checked the lifters and cam last time I had it apart and no wipe lobe or lifters yet.



Does anyone have any ideas what could be causing this? It sounds like I will be pulling the heads again :frown2:






Engine Specs:
.030 over 289. Zero decked

Procomp iron heads milled to 54cc (10.15:1 CR)
Bronze guides, viton valve seals (proper clearance)
Stainless valves

Comp 294S cam (Almost .250" piston to valve clearance)

.030 MLS head gaskets
Comp valve springs (inner spring removed for the break in and no issues with coil bind)
Comp gold 1.6 rockers set at .022" lash
Initial timing set at 12 BTC for break in
Ignition is Summit CDI and billet magnetic distributor
Holley 600 CFM carb, .5" phenolic spacer, Summit 80 GPH mechanical fuel pump
 
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#9 ·
Thanks Allen, I hope you have better luck than I have had. I did not degree the camshaft. I should have I guess, but I just installed it straight up.


Also, I ordered race wheels back in Dec, and got the R888Rs mounted and balanced yesterday. When I went to put them on the car, only 2 fit. 2 were the wrong bolt pattern. I'm just about to lose it with this car!
 
#3 ·
That sucks. Not sure what to say the problem is. Maybe do some exploritory examinations. Remove the plugs, put a ratchet on the balancer bolt and see if you can make a couple complete rotations. See if there’s any noise. If ok, do a compression check then take it from there.

Where the castings new?
 
#14 ·
...it ran great for about 8 minutes until it reached operating temp. Then it totally fell on its face and bogged way down …
What happens when an engine reaches operating temperature? The thermostat opens and the choke opens. Check the choke. Then consider if there is anything else that opens or closes at that point which could affect the engine (not that familiar with your build particulars). Heat riser maybe or something like that?
These are just WAGs, and good luck.
 
#17 ·
Sounds heat related. Something is warming up and getting tight. How did the cylinder walls look when you pulled the heads after the first time?

On a side note, it isn't running out of fuel, is it? How did the fuel bowls look - while it bogs, and immediately after?
 
#26 ·
How did the oil pressure look? Oil temps? Water Temps?

If you pull the valve covers, and turn the engine over by hand, do all the valves stems all move like they should? When you primed the oil pump, there was plenty of oil flowing to the top of both heads?
 
#29 ·
Oil pressure was at 55-60 while running. Oil temp got to maybe 150ish and water 200ish before the problem.


While priming, oil started coming out of the rear pushrods first, and slowly made its way forward. I did not get oil out of all of the front ones during prime, but when pulled the valve cover after it was running, all of the rockers seemed to have plenty of oil on them. Should all the rockers have oil coming out of them while priming within a minute or so?
 
#28 ·
How did you measure Piston to valve clearance? The clay method or with the dial indicator and soft springs? Because you said you did have a valve hit the piston.
 
#31 · (Edited)
First, my condolences. I find it very hard to do things twice- and you’re looking at three times now.
I don’t have enough info to guess- sounds like first time, one valve was bent, but no other smoking gun? Second time just happened so we don’t know.
Let it cool and spin it apart- with more forensics we will walk you through what needs to be verified to help make sure it doesn’t happen again.
 
#33 ·
Sure sounds like it's seizing. Did you get a inspect the cylinders when you pulled the heads. My first thought was Chinese heads perhaps the oil galleries did not line up on the gasket or rocker pedestals. You sure the head gaskets are in correctly? You see where my thought process is going. Maybe pull the pan and make sure the oil pump is installed correctly. make sure none of the journals are starved. This is not something you want happening again.
 
#34 ·
If you zoom in on the picture below, you can see the cylinders. You can see where the rings are running, but nothing out of the ordinary. Chinese castings could be the culprit, but it would be the water galleries not lining up (which could still be the problem if the heads aren't cooling), but they were both full of water when I pulled them the first time. The only place the heads get oil is from the pushrods.

The gaskets are the cometic MLS gaskets and they are clearly marked with a "front" I pulled them off when i had the heads off, and double checked them when I reassembled. Still could be a misstamp or something I suppose.


 
#36 ·
My first guess, based on no abnormal wear showing anywhere, would be too little valve lash, thermal expansion causing the valves to remain partially open. Next would be valves sticking in the guides, followed by lifters sticking the their bores.

You might want to try attaching a vacuum gauge to see what it does once you reach that critical point where performance changes.
 
#38 ·
Valve lash was my thought last go around which is how I found the valve that was stuck open. I did check lash again immediately after it quit this time and it was still set at .022" hot.


We heard what I'm sure was a valve snapping shut about 4-5 seconds after shutting it down this last time which leads me to believe the valves were sticking in the guides again, but what would be causing them to do that if the machine shop took extra care to hone them out slightly larger this time? Cooling issue? Maybe air in the coolant so no coolant actually made it to the head this go around?


Not sure the vacuum gauge would help, as when it bogs down and runs rough, it only lasts about 4-5 seconds before it quits, but I have one I can throw on before running it again.
 
#41 ·
"We heard what I'm sure was a valve snapping shut about 4-5 seconds after shutting it down this last time which leads me to believe the valves were sticking in the guides again, but what would be causing them to do that if the machine shop took extra care to hone them out slightly larger this time? Cooling issue? Maybe air in the coolant so no coolant actually made it to the head this go around?"


Absolutely a cooling problem. Heads are getting (too) hot and guides are seizing the valves. Weak break in springs will magnify that. Air pockets in the heads, mismatched or restricted coolant ports, flow, air, etc. Rather than go back to see what heads you have and lose this reply.... I'll just ask if your heads have any type of temp sensor provision (sender or plug) that you can use to bleed the air from the cooling system/heads. I'd be willing to bet you have a head flow (coolant) problem for whatever reason whether air locked or other.
 
#45 ·
Looking closer at the last photo you posted, the lifter valley appears kind of dry... Safe to assume there aren't any oil restrictors installed?

Don't discount how much cooling the oil does, especially on the top end/valve springs.
 
#52 ·
Have you tried starting it again once it dies? How does it turn over? Easy? Or labored? Could the click you're hearing be your headers cooling and contracting? I get all kinds of pings after shutting down do to contraction. If your engine turns over well after dying, have you verified spark after the incident occurs? The electronic module could be defective and getting heat soaked and shutting down on you.
 
#59 ·
I turned it over by hand last night, everything looked good. No weird sounds or difficulties in spinning it. It's definitely heat related. Could be ignition, but I think it's something mechanical as the very first time it happened I gave it more throttle while it was bogging and it reacted.


The sound I heard could have very well been a header or something but It sure sounded like a valve snapping shut to me.


I am going to talk to the machine shop today and see if they have any ideas, but I'm wondering if it could be something as simple as air bubbles in the heads that are keeping them from cooling. I'm going to get a coolant purge tool and try it again.
 
#60 ·
Did you ever mention what pistons you were running? Forged? hypereutectic? For example, if you have forged pistons but your machine shop provided cylinder wall clearance spec'd for hyper's, you could have the pistons expanding and starting to bind on the walls. Then when it cools they are free again. Hypers can run really tight, like .0015-.002 clearance. Forged pistons can range from .0025-.0065 depending on application and piston material. See page 5 of the uem catalog which discusses alloys and general cylinder wall clearances on application. You'll see that it ranges widely. https://uempistons.com/file/7-Icon+Catalog.pdf The same could be said for the top-ring gap. Many hyper pistons require a greater top ring gap. The summit brand hyper pistons I ran in mine wanted the same gap factor as the keith black ones Which you can find here #2---- Clearance Requirements for Hypereutectic Pistons. With it bogging upon getting hot, it sorta sounds like things are expanding and binding within the engine. Next time you run it and you shut it off due to bog, immediately try turning it over by hand and see how stiff it is. Has your temp gauge shown it to get hot?
 
#66 ·
Did you ever mention what pistons you were running? Forged? hypereutectic? For example, if you have forged pistons but your machine shop provided cylinder wall clearance spec'd for hyper's, you could have the pistons expanding and starting to bind on the walls. Then when it cools they are free again. Hypers can run really tight, like .0015-.002 clearance. Forged pistons can range from .0025-.0065 depending on application and piston material. See page 5 of the uem catalog which discusses alloys and general cylinder wall clearances on application. You'll see that it ranges widely. https://uempistons.com/file/7-Icon+Catalog.pdf The same could be said for the top-ring gap. Many hyper pistons require a greater top ring gap. The summit brand hyper pistons I ran in mine wanted the same gap factor as the keith black ones Which you can find here #2---- Clearance Requirements for Hypereutectic Pistons. With it bogging upon getting hot, it sorta sounds like things are expanding and binding within the engine. Next time you run it and you shut it off due to bog, immediately try turning it over by hand and see how stiff it is. Has your temp gauge shown it to get hot?

The pistons are hypers and the top ring was clearanced to .018" to .020" as instructed. After I ran it today, hot, it felt about normal to turn over with a wrench. The temp gauge did not move before it quit this time. The thermostat didn't open. Water in the radiator just started to get warm and I could still put my hand on the heads after it quit. After it sat around for a minute and the heat made its way into the intake, the temp gauge moved up to about 160.
 
#61 ·
The situation Scarlet describes sounds a bit far-fetched but I'm sure not going to say it's not possible. I second turning the engine by hand when this happens. (Hot) If on the other hand it turns over VERY freely, most likely the valves are too tight. I've run into that myself but mine would actually run OK until it was shut off (to get some gas) and then obviously had no compression when I tried to restart. In any case, you've stated you've turned it more than a little when cold so you should have a good feel for it being easier or not when well warmed up.
 
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