Volvo Penta 8.1 GSI Problems

[SH]

Can any one support claims that these engines have an ongoing <br />"Valve overlap" problem which results in ingression of water back into the engine at low RPM.

 

[newport dave]

Re: Volvo Penta 8.1 GSI Problems

I have not heard of this probelm.<br /><br />I'm not too familiar with the Volvo 8.1, but I can tell you that the Mercruiser 496HO/8.1HO (425HP) engine - when properly installed - does not have a reversion problem. Same base engine, same cam.<br /><br />The real difference in the two is the exhaust system. I know that Mercruisers exhaust elbow is designed to reduce "tuning", the pulsing effect of the exhaust that causes reversion. They also recommend installing "resonators" downstream from the risers in most installations. Not sure about Volvo's exhaust design or installation requirements.<br /><br />My point in all this is that the 496/8.1 engine itself does not have excessive valve overlap - when properly installed and equipped with a properly designed exhaust system.<br /><br />Dave

 

[Richard Petersen]

Re: Volvo Penta 8.1 GSI Problems

HIGH ENOUGH exhaust risers stop reversion problems. Unless the boat is just too low then nothing will stop the reversion. Year of engine and boat it is in would help. Do you know for sure the camshaft is stock? Type and make of exhaust and the height of the riser spacer. Good accurate guess in the difference between waterlevel and the middle of the top riser loop.

 

[rodbolt]

Re: Volvo Penta 8.1 GSI Problems

the reversion problem is there with both the merc and the volvo<br /> the merc risers are turned down a few degrees more than the volvo but both have nuemerous tech bullitens about how to test for reverion. seems its not all overlap but very high pressure pulses in the opposite bank. volvo has a kit that is a baffle as well as a balance tube that crosses the exhaust risers. most common on boats that have a Y pipe or a common collector. the cam shaft is very aggressive and in some cases a 1 foot riser heght wont help. describe your hull and exhaust and the riser X dimension.

 

[SH]

Re: Volvo Penta 8.1 GSI Problems

Thanks, Rodbolt, Cyclops2 and Newport Dave. The vessel is a Doral 360 SE,2002. Volvo claim that they fitted the 7-inch high spacers between the manifold and riser, because of "pressure" issues. An inspection of the valves show that they arent perfectly <br />in sync. Both engines have taken water into the inside banks in the central cyclinders. The vessel was stationary at the time of failure and had just had the engines run at low RPM simply to ensure running condition following a two month lay over at the dock.

 

[newport dave]

Re: Volvo Penta 8.1 GSI Problems

There is a guy on another forum who has the same boat with the same problem. His has Mercruiser 8.1's. <br /><br />If you want I will send you the link.<br /><br />Dave

 

[SH]

Re: Volvo Penta 8.1 GSI Problems

Dave,Thanks, I would appreaciate the link

 

[newport dave]

Re: Volvo Penta 8.1 GSI Problems

http://www.boatered.com/forum/topic.asp?TOPIC_ID=58340

 

[Richard Petersen]

Re: Volvo Penta 8.1 GSI Problems

I am really going to stick my neck out on this one. The risers are probably high enough when the boats prototype was built and tested by a engineer. Then the options are added and weights shift and increase without a reversion check out again. Your problem is probably that. Can you get a clear shot down to the top of any engine riser with the floor / engine hatches open? If yes. A 2" X 4" long enough and straight board with a level taped on top of it and a weighted string off 1 end to water level out side the hull. Other weighted string hangs down and just touches the top of a engine riser. Measure both lengths. Now you have the true MINIMUM riser height. Find out what's really provided. Now you have real riser data to work with.

 

[rodbolt]

Re: Volvo Penta 8.1 GSI Problems

SH<br /> the normal problem with Y pipes or common collectors is when you shut the engine down it uses the exhaust pressure from one bank to force water up the other. the newr MPI engines no longer have an exuast passage under the intake to heat the intake so its a relativly new problem. that and the aggressiveness of the cam. we have had some that would do it 1 out of 5 shutdowns. one cure is to add a 1 1/4" ballance tube. carolina classic uses an elbow with a pipe nipple welded to the top of the elbows. each nipple lays horizontal and a piece of hose connects them. also the elbow has a 1/2" thick plate with about 18 1/2" holes welded in it to break up the exhaust reversion pulses. it will knock a few hundred RPM off the top usually but it seems to work. if you contact carolina classic boats in Edonton NC they may be able to help.