Less than 3000 miles on rebuilt 7m gte (arp rod bolts, arp head bolts, metal gasket, turbo rebuid, etc. but started to have a top end valve type "tap" and thought it had broken a valve spring. A so-called race shop in Nashville, TN did the head overhaul and other machine work, and I've been gently breaking the engine in (never above 5500 rpms) and it seemed to run well. installed the one piece down pipe and free-flow exhaust but still stock intercooler and pipes and BOV. Just pulled the cams to check for broken valve spring but find nothing appears wrong! Thinking it could be a valve guide has come loose and is moving in the head. Tapping will sometimes go away at dead idle but resumes when given even slight throttle. About to pull the head and wonder: how much intake and exhaust can I leave assembled? What's the easiest and best way to do the quick head removal? It seems to be a real pain to get to the intake and exhaust bolts with the engine in the car, but also drag to pull the whole works if not needed. By the way, many years experience on other types of engines makes me think this sound is not piston pin or any bottom end noise. Using a length of hose to listen with I was almost positive the noise was coming from the #5 exhaust valve. It sounds as if the valve is sticking open a bit too long and thus I was guessing a broken spring but using a hammer handle to gently depress each valve slightly seems to show all is well. All ideas greatly appreciated.
recent rebuild now top end "tap"
- Thread starter rustfarmer
- Start date
I vote that your cam bearings are out of spec. You will need to plastigage them unless you have access to high precision metrology. Tough to get a good measurement unless the buckets are off. They tend to open up due to rather poor lubrication, especially the journals in the rear furthest from the oil supply. You can lap the caps to get back. Most of the wear is in the caps.
That sounds like the exact thing mine was doing. It was a tapping not a knocking or a ticking and it kept pace with the ampunt of rpms i gave it. Almost sounded like when u were a kid and put cards in your bike spokes and the faster you pedaled the louder it got. Some times at idle it would go away for a sec and then come back.
I decided to cometely rebuild. First I took the head off, everything inside the head was to specs. No signs of obvious causes in the head itself which completely blew me away as I thought for sure the sound was coming from there. So I kept digging. Noticed a small crack in head gasket (cometic from PO) between cylinder 3and 4. But I thought no way that could be the culprit, so kept digging... put a straight edge on the head and it was warped quite a bit in spots, but there was no coolant or milky color in the oil...
After pulling the rod and main caps off I found a spun bearing on the #3 cylinder, which was razor thin. I am still rebuilding and to this day have no idea which one of those things was the cilprit. I don't want to scare ya just thought I would share that even if it sounds like top end this engine is a deceitful bastard.
I decided to cometely rebuild. First I took the head off, everything inside the head was to specs. No signs of obvious causes in the head itself which completely blew me away as I thought for sure the sound was coming from there. So I kept digging. Noticed a small crack in head gasket (cometic from PO) between cylinder 3and 4. But I thought no way that could be the culprit, so kept digging... put a straight edge on the head and it was warped quite a bit in spots, but there was no coolant or milky color in the oil...
After pulling the rod and main caps off I found a spun bearing on the #3 cylinder, which was razor thin. I am still rebuilding and to this day have no idea which one of those things was the cilprit. I don't want to scare ya just thought I would share that even if it sounds like top end this engine is a deceitful bastard.
Do you have a warranty on the headwork? Anyway, pull each spark plug one by one and see if it stops. If you have the cams out your not real far away. Fastest way is to just unbolt intake and exhaust mani from head and pull head out. I know it sucks since u just rebuilt but it happens just put all your bolts in plastic cups/bags and label them so reassembly is fast. Hope u find the problem. Let us know
If you've traced the loudest point to a specific area in the head I would doubt it's bottom end, but it's not much work to check either. Use the same technique you did on the top end but on the oil pan/side of the block if you want to be sure. I'd still start with checking the valve clearances and make adjustments as necessary. If everything checks out and/or that doesn't solve the issue, move on to checking the cam bearing specs as 3p suggested.
If you do decide to pull the head I've always removed the turbo/exhaust manifold as well as upper intake manifold. I kept the lower intake manifold attached. You should be able to get a good idea of what the issue is without needing to do this though.
If you do decide to pull the head I've always removed the turbo/exhaust manifold as well as upper intake manifold. I kept the lower intake manifold attached. You should be able to get a good idea of what the issue is without needing to do this though.
Thanks for all the ideas guys. The cam "bearings" surfaces do look a bit scored, but not more than when I put it together. Good idea to mike then and check specs which I will do soon. Also thought wrist pin is possible issue but my experience is that will make a double-tap sound usually. No one thinks a valve guide might be loose and moving with the valve? Remember, ran quiet for about 3k after rebuild , then suddenly began rather loud tap.
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The cams/bearing caps almost always look scored on 7M's. It's typically a case of "looks worse than it is" but no harm in checking while you're in there. Cam wear specs can be found here:
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EM&P=48
http://www.cygnusx1.net/Supra/Library/TSRM/MK3/manual.aspx?S=EM&P=48
Yup, they always look bad. They need to be measured, that's the only way to know and it's a pain to do in the car.
A sticking valve is not out of the question either of course. Did the shop replace the seats in the head by any chance?
A sticking valve is not out of the question either of course. Did the shop replace the seats in the head by any chance?
No valve seats were replaced as far as I know, nor were the springs replaced. Follower cups seem pretty good although some have minor pits on sides in the top 1/3 area. All wear on the cups look the same. using the hammer handle to slightly compress the springs all valves seem to be free. Tap noise does not require the engine to be warmed up but instead happens as soon as started. Guess I'll have to pull the head (major PITA and cost of new gasket, etc) and disassemble the valves to figure this one out although I will check the oil clearances and valve lash first. Any other tricks to check for sticking valve?
I'm surprised no one has asked for a video yet
Sent from my terrible HTC Rezound using Tapatalk. Don't buy HTC...
Sent from my terrible HTC Rezound using Tapatalk. Don't buy HTC...
Backlash2032;1893088 said:
Realistically it's hard to diagnose most engine noises properly with the car sitting there beside you running, not to mention over the internet with a video that nine times out of ten is from a phone. The OP has pinpointed the noise already with a stethescope (or in this case a rubber hose) and that's the more important information (assuming they can differentiate a "knock" from a "tap" from a "tick").
I pulled the head today and started checking valve springs, ect. Started with # 5 and although both exhaust seemed ok, one intake valve sticks a bit when slightly opened. It seems to me that the valve springs all are sort of weak so I'm thinking of replacing the entire set. Now for the "rest of the story". Prior to the noise starting we noticed that the engine had begun to use some oil and found that a hose which runs along the side of the accordian hose (about 3/4" diameter) had collapsed nearly flat. Doing the rebuild we could not easily find the stock molded hose so I used a piece of heater hose. I think this hose is part of the PCV system and was causing the oil usage. I noticed the exhaust ports and top of the pistons have a good bit of carbon from burning the extra oil, but the intake ports are mostly clean as the injector spray washes them, but they do have some deposits on the sides where the injectors don't directly spray. These deposits seem like gritty rubber particles and are perhaps from the intercooler pipes (old originals) breaking down from the excess oil. Is it possible/likely that this stuff may have coated the valve stems and created a sticky valve? I plan to disassemble each valve and clean them, lube them and install new seals. Also will replace hoses and turbo tubes and clean this also. Other ideas most welcome. PS do the oil filter re-location kits get rid of the big oil filter adapter? Sure could use the extra room.
More reading reveals some guys are running big block chevy inner valve springs on 7m to save much $ and claim the stock springs are weak. Any thoughts?
I run them.
They're a bit stronger than the stock units, and aren't 20+ years old.
I haven't heard of anyone ever having trouble with them.
They're a bit stronger than the stock units, and aren't 20+ years old.
I haven't heard of anyone ever having trouble with them.
my vote would be worn out valve springs...IIRC stock valve springs are rated at 33ft lbs
after many years and heat cycle's they weaken
just had my 7m head rebuilt(had 78k miles) replaced all springs with BBC comp cam valve springs...24.99 a box from summit racing
anyway the stock springs that where pulled out had broken down to 22ft lbs of pressure
the BBC comp cam springs are 55ft lbs of pressure
(dont have current specs of valve springs for exact height-pressure specs)
after many years and heat cycle's they weaken
just had my 7m head rebuilt(had 78k miles) replaced all springs with BBC comp cam valve springs...24.99 a box from summit racing
anyway the stock springs that where pulled out had broken down to 22ft lbs of pressure
the BBC comp cam springs are 55ft lbs of pressure
(dont have current specs of valve springs for exact height-pressure specs)
adampecush;1893349 said:
Have you done this??? Are they all in spec? Tapping noise that matches RPM's and burning oil does sound like rod knock to me. I hope I'm wrong here.
I just recently installed BBC springs on my car. No problems installing them, and they're just as quiet at stockers. Feels a little better in the upper RPM range, but my turbo just took a dump on me. Springs had nothing to do with that. I think I just somebody's elses problem when I bought this turbo used several years ago, but that's another story.
I vote shims as well.
When they're beyond clearance, they sound like injectors ticking away, but alot louder.
When they're beyond clearance, they sound like injectors ticking away, but alot louder.
But why would a just rebuilt engine with perfectly shimmed valves suddenly develop a lash problem? I like the worn out springs together with a sticky valve. Not saying it can't be something else, but it really sounds like a valve and the lash is ok.